声波导中的局部正交变换

In this paper, a local orthogonal transformation is created to transform the Helmholtz waveguide with curved interface to the one with a flat interface within the two-layer medium, and the Helmholtz equation uxx uzz k^2(x,z)u=0 is transformed to Vxx αVzz βVz γV=0. Numerical results demonstrate that the transformation is more feasible. This transformation is particularly useful for the research on wave propagation in acoustic waveguide.     

Noise Stability of SIS Receivers

There is a strong interest in the submillimeter astronomy community to increase the IF bandwidth of SIS receivers in order to better facilitate broad spectral linewidth and continuum observations of extragalactic sources. However, with an increase in receiver IF bandwidth there is a decrease in the mixer stability. This in turn effects the integration efficiency and quality of the measurement. In order to better understand the noise mechanisms responsible for reducing the receiver stability, we employed a technique first described by D.W. Allan and later elaborated upon by Schieder et al. In this paper we address a variety of factors that degrade the noise stability of SIS receivers. The goal of this exercise is to make recommendations aimed at maximizing SIS receiver stability.     

有限温度下二维Heisenberg铁磁系统的声子衰减

在二维正方Heisenberg铁磁系统的基础上建立了磁振子-声子相互作用模型. 利用松原格林函数理论研究了系统的声子衰减，计算了布里渊区的主要对称点线上的声子衰减曲线. 发现在第一布里渊区，在Δ线上，横向声频支声子无衰减，在Z线上，纵向声频支声子无衰减；横向声频支声子衰减比纵向声频支声子衰减至少大一个数量级，并讨论了各项参数的变化对横向声频支声子衰减与纵向声频支声子衰减的影响. 根据声子衰减与声子寿命的关系，声子衰减与声子态密度的关系，可以讨论横向声频支声子与纵向声频支声子的寿命与态密度. 关键词： 磁振子-声子相互作用 横向声频支声子衰减 纵向声频支声子衰减 声子寿命     

晶场二级效应与交换作用对PrF3晶体磁性及磁光性质的影响

研究了晶场二级效应在PrF₃晶体中的作用，发现该效应可使Pr³⁺离子的晶场单态与其他态混合，对PrF₃晶体磁化率产生明显影响.进一步研究了晶体内的交换作用有效场，其形式为H_in=(1.9-0.02556T)×10^-5M，在100—300 K的温度范围内，以此计算的PrF₃晶体的倒数磁化率和Verdet常数的倒数与实验值符合较好.结果表明，在PrF₃晶体中，晶场二级效应与离子间的交换作用都不能忽略. 关键词： 晶场二级效应 交换作用有效场 Verdet常数 3晶体')" href="#">PrF₃晶体     

Ternary eutectic growth of Ag-Cu-Sb alloy within ultrasonic field

The liquid to solid transformation of ternary Ag42.4Cu21.6Sb36 eutectic alloy was accomplished in an ultrasonic field with a frequency of 35 kHz, and the growth mechanism of this ternary eutectic was examined. Theoretical calculations predict that the sound intensity in the liquid phase at the solidification interface increases gradually as the interface moves up from the sample bottom to its top. The growth mode of (ε θ Sb) ternary eutectic exhibits a transition of "divorced eutectic- mixture of anomalous and regular structures-regular eutectic" along the sample axis due to the inhomogeneity of sound field distribution. In the top zone with the highest sound intensity, the cavitation effect promotes the three eutectic phases to nucleate independently, while the acoustic streaming efficiently suppresses the coupled growth of eutectic phases. In the meantime, the ultrasonic field accelerates the solute transportation at the solid-liquid interface, which reduces the solute solubility of eutectic phases.     

激光清洗实时监测技术研究

针对目前在研激光清洗的实时监测问题进行实验和分析。得出两个结论:激光清洗具有传统方法无法具有的优越性,可以节省大量人力物力成为新型清洗方法而受到重视,激光清洗在设备维修保养中显示了良好的应用前景。激光清洗过程中产生的声发射信号包含了清洗过程的大量信息,利用声发射检测系统可以对激光清洗过程实时监控。     

基于基团贡献法的HFC＋HC混合物气液相平衡性质预测

基于基团贡献法的思想,本文采用改进的SRK状态方程和修正的MHV1混合规则,将UNIFAC基团贡献法扩展用于HFC HC二元混合物气液相平衡性质的描述,给出了基团划分表和基团间的相互作用参数,使用该方法可以较好地再现HFC HC二元混合物的气液相平衡性质,并且具有良好的预测效果.     

Effect of magnon–phonon interaction on transverse acoustic phonon excitation at finite temperature

A magnon–phonon interaction model is developed on the basis of two-dimensional square Heisenberg ferromagnetic system. By using Matsubara Green function theory transverse acoustic phonon excitation is studied and transverse acoustic phonon excitation dispersion curves is calculated on the main symmetric point and line in the first Brillouin zone. On line Σ it is found that there is hardening for transverse acoustic phonon on small wave vector zone (nearby point Γ), there is softening for transverse acoustic phonon on the softening zone and there is hardening for transverse acoustic phonon near point M. On line Δ it is found there is no softening and hardening for transverse acoustic phonon. On line Z it is found that there is softening for transverse acoustic phonon on small wave vector zone (nearby point X) and there is hardening for transverse acoustic phonon nearby point M. The influences of various parameters on transverse acoustic phonon excitation are also explored and it is found that the coupling of the magnon–phonon and the spin wave stiffness constant play an important role for the softening of transverse acoustic phonon.     

Application of inertia-induced excitation theory for nonlinear acoustic modes in colloidal plasma equilibrium flow

Application of inertia-induced acoustic excitation theory offers a new resonant excitation source channel of acoustic turbulence in the transonic domain of plasma flow. In bi-ion plasmas like colloidal plasma, two well-defined transonic points exist corresponding to the parent ion and the dust grain-associated acoustic modes. As usual, the modified ion acoustic mode (also known as dust ion-acoustic (DIA) wave) dynamics associated with parent ion inertia is excitable for both nanoscale-and micronscale-sized dust grains. It is found that the so-called (ion) acoustic mode (also known as dust-acoustic (DA) wave) associated with nanoscale dust grain inertia is indeed resonantly excitable through the active role of weak but finite parent ion inertia. It is interestingly conjectured that the same excitation physics, as in the case of normal plasma sound mode, operates through the active inertial role of plasma thermal species. Details of the nonlinear acoustic mode analyses of current interest in transonic domains of such impure plasmas in hydrodynamic flow are presented.      

Fracture of diamond coatings by high velocity sand erosion

This paper describes a study of the behaviour of diamond coatings when subjected to solid particle erosion from sand particles. The coatings were deposited by chemical vapour deposition (CVD) onto tungsten substrates and tested using a high velocity air–sand erosion test facility. The erosion tests were conducted using particle impact velocities of between 33 and 268 m/s. Examination of the eroded test specimens showed that the principal damage features were circumferential cracks and pin-holes. Comparison with Hertz impact theory revealed that the measured circumferential crack diameters were more than double the predicted Hertzian contact diameter. Moreover, a trend of increasing circumferential crack diameter with coating thickness, which is not predicted by Hertz, was found. Instead, the crack diameters showed good agreement with those predicted by the theory of stress wave reinforcement, which is more commonly associated with liquid impact damage of brittle materials. During impact, the bulk compression and shear waves are reflected at the rear surface of debonded regions of the coating to return to the front surface and reinforce the Rayleigh surface wave, which generates a tensile stress. Where this stress exceeds the local tensile strength of the coating, a ring of cracks surrounding the area of impact is created. The results from the present study therefore suggest that stress wave reflection is responsible for the formation of the cracks at locally debonded regions of the coating. This hypothesis was supported by images acquired using scanning acoustic microscopy, which showed that circumferential cracks and pin-holes were only found on areas of the coating that had become delaminated by multiple particle impacts during the erosion tests.