结构声辐射的振动模态分析和声辐射模态分析研究

基于辐射声功率的二次型表达式,采用有限元法、Rayleigh积分和边界元法对结构声辐射进行了振动模态分析和声辐射模态分析研究。振动模态间的耦合对辐射声功率影响的研究表明:结构各阶振动模态自身对结构辐射声功率的贡献是增大结构的辐射声功率,而振动模态间的耦合可能会增大结构辐射声功率,也可能会减小结构辐射声功率,或对辐射声功率没有影响。而且,当振动模态间的耦合作用对辐射声功率的影响不大时,采用振动模态控制可取得较好的减振降噪双重控制效果。将混合的Helmholtz积分方程方法用广义逆引入到三维复杂结构声辐射分析的声辐射模态公式中,解决了特征频率下解不唯一问题。还研究了正方形封闭空间结构声辐射模态的辐射效率和形状,并对结构声辐射的振动模态控制和声辐射模态控制进行了讨论。     

目标角振动的散斑法实时测量

 论述了利用激光散斑实时测量目标散射面角振动的原理，并从干涉条纹的角度对仿真参数进行了分析。理论分析及仿真结果表明，探测器接收的光功率起伏包含了目标散射面角振动的信息，利用散斑实时测量目标角振动是可行的。目标散射面照明尺寸越小，目标散射面绝大多数微元的间距也就控制得越小，探测到的光功率交流分量起伏越大，即信号也越强。光学接收天线光阑边长并不是越大越好，随着其值的增大，光功率交流分量并不是简单的随之增大，而是表现出周期性的起伏。因此，可以对接收天线加可调光阑，从而达到最佳的探测效果。利用此原理构建的系统测量的目标角振动振幅有一定的范围,测量上限受限于相位调制因子。     

Hybrid modes of open waveguide cavities (numerical and analytical investigation)

Conclusions We see that the behavior of the spectral curves near regions of mode interaction can be reconstructed by determining the set of Morse critical points and the expansion (3). If these curves are augmented with corresponding asymptotes of the form Re (L) _n /2L1, Im (L) 0 fairly detailed information can be obtained about the behavior of the eigenfrequencies of the investigated structure. This approach is most effective in cases where mode interaction can be expected beforehand on the basis of general considerations when the sequence of excitation of the OWC and the energy-converting properties of its boundaries are known. By solving Eq. (4), we can predict unambiguously whether such interaction will take place and, if so, for what geometrical and frequency parameters. Once the coordinates of the Morse point are known, the structure of the field can also be effectively and deliberately varied without any appreciable change in the OWC geometry.Institute of Radiophysics and Electronics Academy of Science of the Ukrainian SSR, Kharkov. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 32, No. 8, pp. 1000–1008, August, 1989.     

The effect of angular momentum coupling on the angular distribution of fission fragments

We examine what information can be obtained from fission angular distributions through precise measurements and an analysis in terms of the simple statistical model of Ericson. We report on the systematics of the decoupling angle and present the role of the angular momentum coupling between the entrance and the exit channel. The results indicate that the directional coupling of the angular momentum in the entrance and the exit channel is always strong for heavy-ion induced fission, and the angular momentum coupling plays a decisive role on the angular distribution of fission fragments. The average channel spins of fission fragments 〈I_f〉 are deduced through the decoupling angles determined experimentally. They agree well with γ-multiplicity measurements.     

目标角振动的散斑法实时测量

论述了利用激光散斑实时测量目标散射面角振动的原理,并从干涉条纹的角度对仿真参数进行了分析。理论分析及仿真结果表明,探测器接收的光功率起伏包含了目标散射面角振动的信息,利用散斑实时测量目标角振动是可行的。目标散射面照明尺寸越小,目标散射面绝大多数微元的间距也就控制得越小,探测到的光功率交流分量起伏越大,即信号也越强。光学接收天线光阑边长并不是越大越好,随着其值的增大,光功率交流分量并不是简单的随之增大,而是表现出周期性的起伏。因此,可以对接收天线加可调光阑,从而达到最佳的探测效果。利用此原理构建的系统测量的目标角振动振幅有一定的范围,测量上限受限于相位调制因子。     

Pulsed laser deposition of lysozyme: the dependence on shot numbers and the angular distribution

An efficient near-infrared (NIR) quantum cutting (QC) by converting ultraviolet into NIR via cooperative downconversion (DC) for the (Nd³⁺, Yb³⁺) couple in CaWO₄ is studied since efficient two-step energy transfer occurs from the ⁴G_9/2 level of Nd³⁺ to two neighboring Yb³⁺:²F_5/2 level. The authors have analyzed the measured luminescence spectra and decay lifetimes for different Yb³⁺ concentrations and proposed a mechanism to rationalize the DC effect. The maximum quantum efficiency (QE) of Nd³⁺ is up to 164.03 %. Application of the broadband NIR-QC phosphors might enhance the performance of silicon-based solar cells.     

Photodestructive effect of IR laser radiation on the cornea

A mathematical model of the photodestructive effect of high-power IR laser radiation on cornea tissues is presented. The threshold energy exposure is calculated as a function of the wavelength and the laser pulse duration in the range 10^?5–10^?1 s under the assumption that the irreversible primary changes in the structure of tissues have a thermochemical nature. The adequacy of the model is supported by comparison of the results of calculations with a great body of experimental data available in the literature. The model is oriented for use in designing medical equipment (for example, for the refraction correction by the thermal keratoplasty method) and in refining the operating laser safety standards.     

板结构的声辐射模态分析及其高分辨率法向振动速度重建

提出了一种基于声辐射模态的速度基向量构建方法,该速度基向量不受网格划分的影响,可用于高分辨率的板结构法向振动速度重建。首先对板表面稀疏网格的声辐射模态进行计算,再以声辐射模态和模态系数构建板法向振动速度分布的基向量,然后由声场测量声压求解基向量系数,最后由该系数和加密网格的速度基向量重建高分辨率的板法向振动速度分布。以简支板声源进行仿真计算,当测量声压信噪比为30 dB时,低频的法向振动速度重建误差最低可达3.7%;以固支板声源在消声室中进行实验验证,131.5 Hz振动频率下的重建误差低于7%。该方法实现了只需要少量声压测量点即可精确重建板声源更高分辨率的法向振动速度分布。     

Considerations on the determining factors of the angular distribution of emitted particles in laser ablation

Simulations of particles which are emitted in laser ablation have been performed by the method of Direct Simulation Monte Carlo to investigate the deposition profiles of the emitted particles. The influences of the temperature, pressure and stream velocity of the initial evaporated layer formed during laser ablation process on the profile of the deposited film have been examined. It is found that the temperature gives a minor influence on the deposition profile, whereas the stream velocity and the pressure of the initial evaporated layer have a greater impact on the deposition profile. The energy in the direction of surface normal (E_⊥) and that in the parallel direction of the surface (E_||) are shown to increase and decrease, respectively after the laser irradiation due to collisions between the emitted particles, and this trend is magnified as the pressure increases. As a consequence, the stream velocity in the direction of surface normal increases with the increase in the pressure. A mechanism of the phenomenon that a metal with a lower sublimation energy shows a broader angular distribution of emitted particles is presented. It is suggested that low density of evaporated layer of a metal with a low sublimation energy at its melting point decreases the number of collisions in the layer, leading to the low stream velocity in the direction of surface normal, which results in the broader deposition profile of the emitted particles.     

Effect of quantum interference processes on the angular distribution of the spontaneous radiation in the D line of alkali-metal vapors in a laser wave field

The resonance fluorescence of a degenerate V-type three-level atom in the field of an intense monochromatic wave with arbitrary polarization composition is investigated. The equations of motion, the general form of the radiation relaxation operator, and the analytical expressions for the angular distribution of the intensity of the spontaneous radiation from atoms, and the total intensity of the resonance fluorescence for such systems are obtained. The angular distribution of the spontaneous radiation from atoms for the D line of alkali-metal vapors is investigated. It is predicted theoretically that the intensity of the resonance fluorescence will decrease as the intensity of the pump wave increases in observations in a direction of the electric field vector of the laser wave.     

The focusing effect on the angular distribution of the Raman antiStokes branch emissions

The angular distributions of the 1st to 3rd antiStokes emissions produced by Nd:YAG pumping a H₂ high pressure Raman cell have been measured and explained as a consequence of the destructive interference of the Stokes-antiStokes interaction.     

Torque equations for spin and orbital angular momenta of radiation fields and Faraday effect

The spin angular momentum S of light has never been linked to the Faraday rotation of light traveling in an optically active medium possessing a rotational invariance of a crystal, because there was no helicity term associated with the phase shift in the previous torque equation for S. In order to relate the change in S with time to the Faraday rotation, therefore, we derived an exact torque equation for S. As a result, a magnetic helicity term appeared in a new torque equation for S, so that one-half of the phase shift derived from the helicity term was equivalent to the Faraday rotation angle. However, the orbital angular momentum L had no relation to the Faraday rotation. It was thus clarified that the change in S with time is related to the Faraday rotation angle of light traveling in an optically active medium, owing to the appearance of the helicity term without a rotational invariance around the optical axis. It was also demonstrated theoretically that the Faraday rotation is accompanied by a torque acting on the crystal so that the total angular momentum of light and matter is conserved.