横观各向同性材料中激光超声谱有限元数值模拟

研究了横观各向同性材料中激光超声波的传播特征.基于谱有限元方法,建立了横观各向同性材料中激光超声的数值模型.利用谱有限元方法模拟脉冲激光作用于材料上产生超声波及其传播的过程.讨论了横观各向同性薄板的各向异性及各向同性平面内超声波的传播特征,并分析了材料厚度的变化对产生超声波模态的影响.     

Transverse surface waves in a layered structure with a functionally graded piezoelectric substrate and a hard dielectric layer

As to an ideally layered structure with a functionally graded piezoelectric substrate (material parameters change continuously along the thickness direction) and a hard dielectric layer, the existence and propagation behavior of transverse surface waves is studied by analytical technique. The dispersion equations for the existence of the transverse surface waves with respect to phase velocity are obtained for electrically open and short circuit conditions, respectively. A detailed investigation of the effect of gradient coefficient on dispersion relation, electromechanical coupling factor and penetration depth is carried out. It is found by numerical examples that adjusting gradient coefficient makes the electromechanical coupling factor of the transverse surface waves achieve quite high values at some appropriate ratio values of the layer thickness to the wavelength, and at the same time, the penetration depth can be reduced to the same order as the wavelength.     

回旋速调管双阳极磁控注入电子枪的设计与优化

 根据8 mm回旋速调管放大器对双阳极磁控注入电子枪的要求，分析了电极形状、阳极电压、磁场、注电流对电子注横纵速度比和速度零散的影响，并进行了粒子模拟。分析表明：这些因素可归根为电场和磁场的作用，阴极附近高的电场有助于提高横纵速度比和降低速度零散；而高的磁场及低的磁压缩比将降低横纵速度比，但对速度零散影响无明显规律。在此基础上通过优化电极形状、磁场分布、电流、第一阳极电压和第二阳极电压，模拟并试制出工作电压65 kV、电流12 A、磁场1.4 T的双阳极电子枪，得到的横纵速度比值为1.4，横向速度零散为4.5%， 为8 mm回旋速调管提供了稳定高质量的电子注。     

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.     

Influences of the Current Transverse Profile on the Transverse Mode Competition of VCSELs Diodes

A spatially independent model of vertical-cavity surface-emitting lasers (VCSELs) is derived by integrating the spatially dependent rate equations over the cross section of the cavity of a VCSEL. The angular and radial non-uniformities of the injection current are taken into account. The well-known LP modes of a weakly-guiding cylindrical waveguide are employed to describe the transverse modal structure in the VCSEL cavity. This model is solved in a self-consistent way by using the 4th order Runge-Kutta method. The dependence of transverse mode competition on the current intensity, the angular and radial non-uniformities of the injection current, and the geometrical parameters of the electrical contact are thoroughly investigated and analyzed. The results are useful to the optimum design of the optical transverse modal structure of VCSELs.     

超级活性炭的合成及活化反应机理

以石油焦为原料,采用碱熔活化法合成出具有超高比表面的超级活性炭.借助XRD、TG DTA、N2吸附实验等手段,对其结构与性能进行了表征.同时,设计原位TG DTA测试技术、反应快速终止技术,对超级活性炭合成机理进行了考察,提出了两段活化反应机理,即中温径向活化机理和高温横向活化机理.发现K2O、－O－K＋以及－CO－2K＋是径向活化为主的中温活化段的活化剂活性组分,而处于熔融状态的K＋O－、K＋则是横向活化为主的高温活化段的催化活性组分.并发现径向活化是超级活性炭形成发达微孔分布的主要途径,也是控制超级活性炭微孔分布的主要手段.而高温横向活化机理则是导致超级活性炭形成大孔的主要途径.高温横向活化与中温径向活化一起构成石油焦基超级活性炭形成的主要机理.     

Fast determination of evaporation enthalpies of solvents and binary mixtures using a microsilicon chip device with integrated thin film transducers

A silicon chip device with two types of integrated platinum thin film resistors was applied for microcaloric measurements. It was shown that the device is capable of fast characterization of liquid evaporation behaviour and allows the determination of evaporation enthalpies for pure liquids and mixtures. The applicability was demonstrated for a wide range of solvents from nonpolar aliphatic solvents over polar organics to protic solvents (e.g. iso-octane, toluene, acetone, ethanol, methanol and water). The sample volumes were in the range of about 2-5 μL. The determination of transient times, in case of constant power mode, or the power integral over time was used for the fast estimation of binary liquid mixtures. Thermo-resistive measurements of 5 μL droplets of solvent mixtures like methanol/iso-propanol, ethanol/water, iso-octane/iso-propanol and iso-octane/1,4-dioxane showed significant changes in temperature characteristics and evaporation enthalpies in dependence on composition. The applied heating power was about 1 W, which corresponds to measurement times between a few seconds and a minute.     

Application of trilinear SLICING to analyse a single relaxation curve

Determining the time constants and amplitudes of exponential decays from relaxation data is a common task in LF-NMR. In this communication, we present an application of the SLICING algorithm to evaluate its possibilities for solving this problem. The method, originally introduced to compare different samples, is applied here to analyse a single relaxation curve, using the embedding technique. To test this procedure, we acquired data sets from samples of liquids properly separated, and characterized by different relaxation times. The results show a good estimation of parameters, comparable with those obtained applying Marquardt's algorithm, when the components have sufficiently different relaxation times.     

Full-wave modeling of piezoelectric transducers for SAW acousto-optical interactions

In this paper we present an accurate and efficient numerical method for a rigorous full-wave analysis of interdigital transducers (IDT) for the excitation of surface acoustic waves on the piezoelectric substrate of acousto-optical devices. The problem is formulated in terms of an integral equation that is solved by the method of moments. The transducer input admittance and the power coupling factors to both surface and bulk waves are computed. Numerical results for some configurations of X-Y LiNbO₃ IDT for acousto-optic applications are in very good agreement with measured data. It is pointed out that bulk wave excitation may be a serious limitation in the design of efficient, wide band transducers for acousto-optical devices.     

阶跃光纤的偏振色散

利用全反射光在光纤包层中的横向偏移和渡越时间,导出了各向同性光纤的全反射偏振色散公式及双折射光纤偏振色散的修正公式,通过模拟计算分析了偏振色散随入射角的变化规律.