Parametric decay instabilities of the fast wave in the lower hybridfrequency regime

Three possible delay instabilities of the fast wave in the lower hybrid frequency regime are presented. It has been considered that a fast wave may decay into a high-frequency, lower hybrid wave and a low-frequency wave, either the ion-Bernstein wave, ion-acoustic wave, or kinetic Alfven wave. Explicit expressions for growth rates, homogeneous thresholds, and convective thresholds have been given. Applications have been pointed out in tokamak plasma during current drive experiments and magnetospheric plasmas. For example, for PLT tokamak parameters, the convective threshold for the decay instability of the fast wave into lower hybrid and ion acoustic wave is ~180 W/cm²     

研究温度波的传播特性

根据振动与波的原理,把样品上某点温度随时间的周期性变化看作一种振动,把这种温度变化向外传播的过程看作波动,引进温度波,说明样品上各点温度随时间、距离的变化;采用一维模型,写出温度波的传播方程.考虑到样品(铜棒)散热,引进衰减系数,描述温度幅度随频率及传播距离的变化关系.利用傅里叶变换分析实验数据,得到温度波幅度与角频率、位置的对应关系.根据温度幅度衰减公式拟合数据,算出基频及倍频对应的衰减系数.结果说明:衰减系数与温度波的频率相关,温度波的频率越高,衰减系数越大,温度幅度衰减得越快.     

Generalization of the Brewster phenomenon for the wave diffraction process

Polarization anomalies of the Brewster type are considered for processes such as wave reflection, wave scattering, wave diffraction by surface grating and surface plasmon waves. Generalized conditions for Brewster anomalies in wave diffraction are written in analytical form. The application of the Brewster phenomenon for integrated optical polarizers is investigated numerically.     

离散可激发介质中早期后去极化对螺旋波影响的数值研究

通过考虑某些不应态也可以被激发,在离散可激发介质Greenberg-Hasting模型中引入早期后去极化行为,研究了早期后去极化对螺旋波的影响.数值结果表明:在适当选择参数下,早期后去极化对螺旋波有很大影响,这些影响包括使螺旋波漫游、漂移和破碎,导致螺旋波波纹被扭曲和波臂粗细交替变化,以及导致螺旋波的周期在两个值之间交替变化,产生从稳定螺旋波到呼吸螺旋波和反螺旋波的相变等.当不应态的激发阈值很高时,早期后去极化对螺旋波没有影响.对发生上述现象作了简要的讨论. 关键词： 离散可激发介质 螺旋波 早期后去极化     

Control over the instability wave in terms of the two-dimensional model of a nozzle edge

The problem of generation of an instability wave leaving the edge of a half-plane that separates an immobile medium from a moving medium is considered. It is assumed that the instability wave is initiated by an acoustic wave arriving from the moving medium. The possibility of suppressing the instability wave by another acoustic wave incident from the nonflowing medium is considered. It is shown that the suppression is always possible by adjusting the amplitude and phase of the control perturbation to the parameters of the instability wave.     

约束层对激光驱动冲击波压力影响机理的理论研究

针对刚性约束层、柔性约束层以及液体约束层，从激光诱导冲击波阵面状态、汽化物(包括气体和等离子体)扩散以及冲击波的反射进行分析，发现对于脉宽小于冲击波通过汽化物层的时间间隔的短脉冲激光，约束层并不能直接提高冲击波的冲量，而对于脉宽大于冲击波通过汽化层时间间隔的激光，其增强冲击效果是通过约束汽化物的扩散，提高压力幅值和由于冲击波在约束层与工件表面的多次反射而延长对工件的作用时间来实现的.刚性约束层能最大地增加冲击冲量，而柔性约束层和液体约束层的主要优点是其形状可与非平面形工件表面符合. 关键词： 激光 约束层 扩散 反射波     

二维水槽中岩石坠落激发表面波的生成机制

针对二维水槽中岩石坠落激发表面波的生成机制进行数值和实验室研究,其中数值模型使用边界元方法求解完全非线性势流函数,实验室研究测得不同时刻的波面位移并用于检验数值模型.研究表明,数值结果和实验结果比对良好,这种基于势流函数理论的数值模型能够有效模拟水中岩石坠落激发表面波的生成过程.进一步数值研究了生成波最大位移随岩石大小、密度、初始位置和下落角度的变化,结果发现：岩石大小和密度对生成波最大位移的影响非常重要,而岩石初始位置和下落角度对生成波最大位移的影响较为显著.当岩石大小变大,密度变大,岩石初始位置更靠近 关键词： 水中岩石坠落 波浪生成 边界元方法 波浪破碎     

超流氦浴中的热波传热研究

热波传热机制是超流氦传热非常重要的一个方面.在小热流密度的情况下,超流氦中的热波完全保持加热热流的波形,热量的传输完全靠热波来完成;随着热流密度的增加到一定程度,会在超流氦浴中激发量子涡旋.量子涡旋使热波发展成为热激波.在开放氦浴中,热波的波形不同于狭窄通道里的热波,在热波的尾部会出现一个冷却波;并且随着加热时间的变化,冷却波的形状和幅度会发生很大的变化.运用二流体模型和涡旋方程对超流氦中的热波进行了计算,实验结果与计算结果吻合得较好. 关键词： 超流氦 热波 量子涡旋 热激波     

通过滤波检测水泥胶结质量的超声反射法

为防止流体沿井轴向窜槽,水泥与套管和地层的胶结必须是良好的。在固井质量检测中,超声反射法因具有较强的方位指向性而被广泛使用。但套管的高声阻抗导致了套管后的反射波信号比较微弱,使得水泥胶结质量的判别变得困难。为提高超声反射法的识别能力,我们以套管的共振频率为中心频率对反射全波进行滤波,降低套管的前表面反射波幅度,凸显套管后面携带水泥胶结信息的反射波。滤波后的波形呈现出数个波包,不同胶结情况下这些波包的幅度存在明显差异,通过这些差异可以判断水泥胶结质量。我们还利用有限声束模型计算了斜入射时的反射全波,探讨了入射角对超声反射波的影响。      

相对论效应对大振幅电子等离子体振荡破裂影响的数值模拟

通过数值求解符拉索夫方程和泊松方程，研究了相对论效应和温度效应对等离子体振荡破裂的影响. 不考虑相对论效应情况下，初始扰动幅度较小时，不会发生等离子体振荡破裂，系统具有时间周期性. 此时电子温度的增加，会使得等离子体振荡最大幅度减小. 考虑相对论效应时，即使初始的等离子体电子密度扰动幅度不大，随着时间演化，相对论效应也能导致等离子体振荡破裂，而且初始电子密度扰动越小，产生等离子体振荡破裂所需时间越长. 在初始电子密度扰动较大时，无论考虑和不考虑相对论效应都会出现波破裂，但两者的结果有很大不同. 此外温度效应会降低能发生等离子体波破裂的阈值；等离子体波的相速度越大，能产生的波破裂现象也越明显. 关键词： 等离子体振荡 相对论效应 振荡破裂     

A separable parametrization of the trinucleon wave function with the Reid soft-core potential

We present a useful analytical parametrization of the bound trinucleon wave function obtained from solving the Faddeev equations with the Reid soft-core potential. The partial wave components of the wave function are expanded in separable terms having rational fraction forms which incorporate the appropriate asymptotic behaviors. Both momentum and configuration space representations of the parametrized partial wave components are presented.     

The kinetic theory of the perturbations in the isotropic universe

The short wave and long wave gravitational perturbations in the isotropic universe are considered by using the general relativistic kinetic theory. It is shown that the short wave perturbations propagate in the ultrarelativistic collisionless gas with the velocity of light.     

Observation of the ionization wave and the shock wave ahead of the plasma jet generated in the plasma focus discharge

An ionization wave travelling ahead of the shock wave of the plasma jet, propagating in residual gas (nitrogen) of the plasma focus discharge, is detected by the laser-interferometry method at the plasma focus. Radial and axial distributions of electron densities of the shock wave and plasma jet are measured.     

孔隙地层井壁上的声波首波及其诱导电磁场的原因

声波测井时孔隙地层中的声波首波平行于井轴沿井壁传播，它既有轴向位移分量，又有垂直于井壁的位移分量.这种以快纵波速度传播的波, 不仅含有由快、慢纵波势给出的梯度场,而且还含有由横波势给出的旋度场.慢纵波势的梯度是渗流位移首波的主要构成成分, 也是声电效应测井响应中存在伴随声波首波电场的主要原因.首波包含有旋度位移场，是存在伴随声波首波磁场的原因. 关键词： 孔隙介质 声波首波 诱导电磁场 测井     

双势阱产生正负电子对过程中的正电子波干涉与克莱因隧穿现象

通过将狄拉克场量子化并且数值求解狄拉克方程的方法研究在一维情况下双势阱激发正负电子对产生的过程.研究发现双势阱激发的正电子波在双势阱之间会出现干涉现象,过程中伴随着克莱因隧穿效应,并且在双势阱之间的距离取正电子波对应的驻波条件时,在双势阱之间会表现出驻波形式的正电子干涉波.并且驻波的出现对正负电子对的产生过程也存在相应的影响,驻波最终会通过克莱因隧穿效应衰减消失.     

Electrostatic Waves in the Warm Magnetoplasma at the Cyclotron Harmonic Frequencies

Mode conversion and collisionless absorption of electromagnetic wave at the cyclotron harmonic frequencies in an inhomogeneous non-Maxwellian magnetoplasma have been studied. Under suitable energy transfer condition the converted electrostatic wave (plasma wave) either grows or damps. The expressions for the growth/damping rates of this wave have been derived and studied at the cyclotron harmonic frequencies. The effect of the temperature anisotropy on the growth/damping rate of the electrostatic wave at the second cyclotron harmonic frequency has been shown. Growth of such electrostatic waves at ionospheric heights may explain the observed upper hybrid resonance (UHR) echoes and noise bands at the second cyclotron harmonic frequency.     

光纤喇曼放大泵浦光与信号光的关联研究

分析了信号光入射后可能发生的效应基于电磁场理论,综合光纤受激喇曼散射(SRS)效应、建立了光纤喇曼放大泵浦光与斯托克斯光、信号光的关联方程,给出了系统增益形成正反馈条件的表达式,结果表明:在光纤参量满足增益正反馈的条件下,当SRS增益对应于非饱和增益工作状态时入射信号光得到放大,SRS增益愈高则放大倍数愈高,并有区段上SRS增益相对低时其关联程度相对高.     

Knotted Wave Dislocation with the Hopf Invariant

We study the wave dislocations with an induced gauge potential. The topological current characterized the wave dislocations is constructed with the dual of Abelian gauge field. And the topological charges and locations of the wave dislocations are determined by the φmapping topological current theory. Furthermore, it is shown that the knotted wave dislocations can be described with a Hopf invariant in the wave field. At last we discussed the evolution of the knotted wave dislocations. PACS 02.10.Kn, 02.40.-k, 11.15.-q     

Electromagnetic fields in a waveguide with a modulated filling near the frequency of resonant interaction between the signal wave and modulation wave

The interaction between a transverse-electric (TE) signal wave and a periodically modulated wave in a waveguide of arbitrary cross-section is considered. The wave equation for the potential of TE field near the frequency of resonant interaction between the signal wave and modulation wave is solved, using the double-scale expansion method. The fields in the first approximation with respect to the modulation indices are obtained.     

Bifurcation of the Biot slow wave in a porous medium

The propagation of the Biot slow wave in a fluid-saturated porous medium at low frequencies is investigated by asymptotic methods. It is proven that the Biot wave has a bifurcation behavior depending on its wave number. The bifurcation occurs in a neighborhood of the critical value k(cr), which depends on the permeability of a medium and the viscosity of a fluid. The P2 wave is fully attenuated if its wave number is smaller than k(cr) and it becomes propagatory with wave numbers bigger than k(cr). Asymptotic formulas for the phase velocity and attenuation of the Biot wave are derived.