液态Sn的粘度及其熔体微观结构的变化

通过对液态Sn的粘度的系统测量和分析,借助DTA-TG综合热分析方法,研究了金属熔体Sn的粘度随温度变化的规律和熔体微观结构的变化.结果表明,Sn熔体的粘度随温度的变化呈明显的不连续性,根据粘度的变化可以将熔体状态分为高温区、中温区和低温区,各温区间存在粘度突变温度点.在突变温度点处,金属熔体Sn可能发生了微观结构的变化.?     

基于温度效应的无限长压电圆杆纵波分析

利用有限变形理论,以无限长压电圆杆为研究对象,考虑了在横向惯性、等效泊松比效应以及在热电弹藕合共同作用下,基于Hamilton原理,并引入Euler方程推导出压电圆杆的纵向波动方程.采用Jacobi椭圆函数展开法,求解压电圆杆的波动方程和对应的解.最后,通过Matlab软件得到不同波速比下的色散曲线.以及温度场对压电圆杆的波形、波幅和波数的影响曲线.数值分析结果表明:随着温度的升高,波速逐渐降低,温度场的改变可影响和控制孤立波的传播特性.     

基于广义交替数值通量的局部间断Galerkin方法求解二维波动方程

波的传播往往在复杂的地质结构中进行,如何有效地求解非均匀介质中的波动方程一直是研究的热点.本文将局部间断Galekin(local discontinuous Galerkin, LDG)方法引入到数值求解波动方程中.首先引入辅助变量,将二阶波动方程写成一阶偏微分方程组,然后对相应的线性化波动方程和伴随方程构造间断Galerkin格式;为了保证离散格式满足能量守恒,在单元边界上选取广义交替数值通量,理论证明该方法满足能量守恒性.在时间离散上,采用指数积分因子方法,为了提高计算效率,应用Krylov子空间方法近似指数矩阵与向量的乘积.数值实验中给出了带有精确解的算例,验证了LDG方法的数值精度和能量守恒性;此外,也考虑了非均匀介质和复杂计算区域的计算,结果表明LDG方法适合模拟具有复杂结构和多尺度结构介质中的传播.     

非热离子对非均匀碰撞热尘埃等离子体中三维孤波的影响

从理论上研究了非热离子、外部磁场、碰撞对非均匀热尘埃等离子体中三维非线性尘埃声孤波的影响。运用约化摄动法得到描述三维非线性尘埃声孤波的非标准的变系数Korteweg-de Vries(KdV)方程。然后把非标准KdV方程变为标准的变系数KdV方程,并且得到了标准的变系数KdV方程的近似解析解。由此解析解可以看出,非热离子的数目、碰撞、非均匀性、波的斜向传播、尘埃颗粒和非热离子的温度对三维非线性尘埃声孤波的振幅和宽度有很大的影响。外部磁场对三维非线性尘埃声孤波的宽度有影响,而对其振幅没有影响。此外,波的相速度与非热离子、波的斜向传播、尘埃颗粒的温度和非均匀性有关。     

内嵌定向高导热层疏导式结构热防护机理分析

针对飞行器高超声速飞行时严重的气动加热环境, 提出内嵌定向高导热层的疏导式热防护系统. 运用数值方法分析了特定条件下内嵌定向高导热层的疏导式系统的防热效果, 外壁面最高温度下降了9.1%, 内壁面最高温度下降了31.5%, 高温区和低温区都被封闭在外层区域, 内层温度更加均匀, 实现了热流由高温区向低温区的转移, 削弱了高温区的热载荷, 强化了整体结构的热防护能力. 研究表明, 随着气动热流密度比与辐射散热面积比的增大, 疏导结构的冷却效果增强. 本文还对疏导防热系统的结构参数和材料参数对冷却效果的影响进行了分析, 为结构的设计和材料的选取提供一定的依据.     

磁场诱导制备Bi-Mn合金的结构和低温磁性研究

系统研究了在外加诱导磁场下制备的Bi-Mn 6%合金的结构和低温磁特性.结果表明,在外加诱导磁场下制备的Bi-Mn 6%合金呈现典型的双相结构和各向异性特征,MnBi相c轴沿外加诱导磁场方向定向排列.发现MnBi相的矫顽力随温度的升高而增大,而饱和磁化强度则随温度的升高而减小.MnBi相的自旋重定向温度TSR随测量磁场的增大逐渐向低温区移动,在高的外加测量磁场下这种自旋重定向特征消失,发现了TSR随外加诱导制备磁场的增大而逐渐向高温区移动.对磁场诱导制备织构化MnBi相和该类材料磁各向异性能的物理机制进行了分析和讨论.     

质子束能量对ADS无窗散裂靶稳态热输运的影响

本文基于稳态流型采用数值模拟方法计算了加速器驱动次临界堆系统ADS无窗散裂靶的稳态热输运过程,得到了不同能量质子束作用下铅铋合金液体和蒸气中的稳态温度分布。对上述温度场结果进行比较表明,在相同流强下,温度场分布形状随能量改变,最高温度亦随之改变,并且质子束能量越高,最高温度就越大。在250 MeV能量质子束作用下,高温区在气相部分,随着质子束能量增大,高温区转移到质子束轰击铅铋合金液相位置。上述热输运数值模拟结果为ADS无窗散裂靶设计和优化提供了可靠的依据,特别是对未来中国ADS的研究和应用具有重要的学术和应用参考价值。     

各向异性粘弹性孔隙介质地震波场伪谱法正演模拟

地球介质各向异性、粘弹性以及孔隙特征是地震资料描述油气储层时应综合考虑的. 建立了各向异性粘弹性孔隙介质模型，导出了各向异性粘弹性孔隙介质的弹性波波动方程，采用伪谱法正演模拟了各向异性粘弹性孔隙介质地震波，进行了其波场特征分析. 该研究有益于加深对地震波在实际地球介质中传播规律的认识.     

地震波传播路径追踪的波动方程方法

在地震勘探的地震波传播研究中,波场传播路径追踪是一项重要研究内容,通常采用射线理论追踪地震波传播路径.提出一种波动方程波场传播路径追踪方法,首先利用窗口Fourier框架展开技术对源点和目标点的波场进行角度分解,并计算它们的方向照明,然后利用角度相干技术获取源点和目标点间的波场传播路径.该方法可以有效考虑地下非均匀介质对地震波场传播的聚焦与散焦作用.     

非均匀饱含黏性流体孔隙介质中声波传播及井孔声场分析

声波在饱含流体孔隙介质中的传播特性与流体的黏滞性及孔隙介质的非均匀性密切相关.本文在Biot理论基础上,考虑了孔隙流体的剪切应力及孔隙结构的非均匀性,采用含黏性流体孔隙介质中的波动理论,研究了孔隙介质中四种体波的频散和衰减特性,分析了慢横波对快纵波转换散射的影响,进一步推导了孔隙地层井孔中的模式波及其声场的解析解,研究了非均匀孔隙介质中井孔模式波和波列的特征.研究结果表明,含黏性流体孔隙介质中存在慢横波,慢横波的频散很强,其传播特征受到介质孔隙度、渗透率及孔隙流体黏度的影响.在非均匀孔隙介质中,与慢横波相关的剪切应力平衡过程不仅导致快纵波的频散和衰减,还会影响井孔伪瑞利波及斯通利波的传播特征.本文的工作完善了孔隙介质中声波传播的物理机制,为孔隙地层井孔声波的解释与应用提供了理论指导.     

Reflection–refraction of attenuated waves at the interface between a thermo-poroelastic medium and a thermoelastic medium

Phenomenon of reflection and refraction is considered at the plane interface between a thermoelastic medium and thermo-poroelastic medium. Both the media are isotropic and behave dissipative to wave propagation. Incident wave in thermo-poroelastic medium is considered inhomogeneous with deviation allowed between the directions of propagation and maximum attenuation. For this incidence, four attenuated waves reflect back in thermo-poroelastic medium and three waves refract to the continuing thermoelastic medium. Each of these reflected/refracted waves is inhomogeneous and propagates with a phase shift. The propagation characteristics (velocity, attenuation, inhomogeneity, phase shift, amplitude, energy) of reflected and refracted waves are calculated as functions of propagation direction and inhomogeneity of the incident wave. Variations in these propagation characteristics with the incident direction are illustrated through a numerical example.     

Ion acoustic solitary wave in an inhomogeneous plasma with non-uniform temperature

A modifiedK-dV equation, which describes the propagation of an ion acoustic solitary wave in an inhomogeneous plasma with both density and temperature gradients, is derived. It is shown that, the velocity of a solitary wave increases as it propagates towards regions of increasing temperature.     

导电介质中电磁波相移常数与振幅衰减常数的方向关系的讨论

对文献上给出的非均匀电磁波在同一均匀导电介质中传播时,电磁波的相移常数和振幅衰减常数方向之间满足定量关系的结论,重新进行了分析和推导,利用电磁波在导电介质界面的边界条件,给出了两种情况下的相移常数和振幅衰减常数的表达式,以及它们与界面法线的夹角正弦的表达式.结果表明,在同一均匀导电介质中,非均匀电磁波的相移常数的方向和振幅衰减常数的方向之间一般不满足定量关系.     

各向异性渗流条件下弹性波的传播特征

研究了弹性波在非均匀裂纹孔隙介质中的传播特性,建立了各向异性喷射流模型.当弹性波通过裂纹孔隙介质时,由于波的扰动及裂纹和孔隙几何结构的不一致,导致在裂纹内部及裂纹与周边孔隙之间同时存在着流体压力梯度.此时的弹性波波动响应中包含着裂纹内连通性特征和背景孔隙渗透率信息.流体的动态流动过程使得介质的等效弹性参数为复数(非完全弹性),并且具有频率依赖性.当弹性波为低频和高频极限时,介质为完全弹性;当处于中间频段时,波有衰减和频率依赖.裂纹孔隙介质的各向异性连通性(渗透率)对应着各向异性特征频率(当渗流长度等于非均匀尺度时的弹性波频率),波的传播受到裂纹内连通性的影响.在一定频段内,随着裂纹厚度的增加,将出现第二峰值,峰值大小同时受到裂纹厚度和半径的影响.     

Angular spectrum approach to electromagnetic wave propagation in inhomogeneous media

The angular spectrum representation of the electromagnetic wave field is employed to solve the wave propagation in a weakly inhomogeneous medium. Taking the two-dimensional spatial Fourier transform of the radiation field as well as of the dielectric constant, the angular amplitude is shown to satisfy an integro-differential equation. A similar equation is also applicable for the propagation of radiation in a non-linear medium. This integro-differential equation is solved for two specific cases of interest, namely that of a stratified medium and of a square-law medium.     

Surface acoustic waves at the vacuum-thermoviscoelastic solid interface

The present investigation concerns the propagation of surface waves at the vacuum-solid interface of a solid which is isotropic and thermoviscoelastic, i.e., for which the effects of heat conductivity need to be taken into account. Calculations show that, in addition to the Rayleigh wave, a thermal surface wave propagates that couples both the thermal and the elasticity effects. This latter wave is interpreted in terms of evanescent plane waves. The displacement field associated with this wave is calculated and interpreted. Some experimental results are also presented.     

Including dispersion and attenuation directly in the time domain for wave propagation in isotropic media

When sound propagates in a lossy fluid, causality dictates that in most cases the presence of attenuation is accompanied by dispersion. The ability to incorporate attenuation and its causal companion, dispersion, directly in the time domain has received little attention. Szabo [J. Acoust. Soc. Am. 96, 491-500 (1994)] showed that attenuation and dispersion in a linear medium can be accounted for in the linear wave equation by the inclusion of a causal convolutional propagation operator that includes both phenomena. Szabo's work was restricted to media with a power-law attenuation. Waters et al. [J. Acoust. Soc. Am. 108, 2114-2119 (2000)] showed that Szabo's approach could be used in a broader class of media. Direct application of Szabo's formalism is still lacking. To evaluate the concept of the causal convolutional propagation operator as introduced by Szabo, the operator is applied to pulse propagation in an isotropic lossy medium directly in the time domain. The generalized linear wave equation containing the operator is solved via a finite-difference-time-domain scheme. Two functional forms for the attenuation often encountered in acoustics are examined. It is shown that the presence of the operator correctly incorporates both, attenuation and dispersion.     

Electromagnetically induced transparency in degenerate two-level systems

The evolution of an electromagnetic wave with slowly varying polarization, which interacts resonantly with the medium formed by degenerate two-level atoms, is studied using the wave function approach under the conditions of electromagnetically induced transparency. It is shown that the amplitude of the wave field propagates at the velocity of light in such a medium. The equation obtained for the polarization parameter has a solution in the form of a simple wave. The breaking length is determined. It is shown that the velocity of propagation of polarization waves may be much smaller than the velocity of light. The proposed approach is common for two-level systems with an arbitrary degeneracy. The case of a system with Zeeman degeneracy is analyzed in detail. The dependence of the velocity of propagation of the polarization structure on the amplitude and polarization is determined for an arbitrary level degeneracy. The evolution of the polarization structure in such a medium is discussed.     

Interaction of a surface magnetostatic wave with an inhomogeneous granular HTSC medium

In the present paper the dispersion properties of surface magnetostatic waves (SMSWs) propagating in a stratified structure, ferrite film—high-temperature superconducting layer, have been investigated. The problem of SMSW propagation in an inhomogeneous stratified medium has been solved and the dispersion equation has been obtained. In the solution of this problem, the granular nature of the high-temperature superconducting (HTSC) medium and the exposure to a constant magnetization field have been taken into account. Upon exposure to the constant magnetic field the HTSC film becomes an inhomogeneous anisotropic medium with respect to a variable magnetic field. The nonhomogeneous wave equation describing the SMSW field in a granular HTSC medium has been solved by the method of sequential iterations. Corrections for the SMSW velocity and attenuation, calculated with the use of the exact dispersion equation, are significant in comparison with previously obtained approximate values and exceed 20 and 40%, respectively. The method of analyzing electromagnetic fields in inhomogeneous granular high-temperature media can be used to solve some other problems, where spatially inhomogeneous HTSC media are used. Tomsk State University of Control Systems and Radioelectronics. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 45–48, April, 1999.