层状介质平面交界裂纹的弹性波（P波和SV波）散射研究

 本文采用Fourier积分变换,将层状介质的弹性波传递矩阵法推广到含有平面交界裂纹层状介质的弹性渡散射问题,进而把散射问题转化为求解矩阵形式的对偶积分方程。作为特例,文中给出单一弹性层与半空间平面交界裂纹的弹性波散射远场模式,并计算几组不同材料组合情形下的远场模式幅频特性曲线,其数值结果表明幅频特性曲线有共振峰存在。     

Acceleration of particles by shocks in a cosmic plasma

The theory and observational evidence pertaining to particle acceleration by shock waves in astrophysical objects and in space are systematized. Recent works showing observational and theoretical aspects of the problem dealing with shocks in turbulent media are emphasized. The acceleration of particles by shocks in turbulent media is observed in interplanetary space. This acceleration mechanism is of particular interest from the point of view of the origin of cosmic rays, providing the degree form of the spectrum. The index of the spectrum is close to the observable one for galactic cosmic rays. It depends slightly on specific conditions in the acceleration region. Electron and nucleus acceleration in supernova remnants and in radiogalaxies is discussed, and theory and observational data are compared. The theory of particle acceleration by supersonic turbulence is outlined.     

斜爆震波起爆特性及其波系结构研究

本文通过对斜爆震波起爆特性及其波系结构的研究进展进行综合评述,分析其研究现状与存在的不足,指导未来斜爆震波的基础研究。首先总结了斜爆震波起爆和驻定特性研究进展,重点回顾了斜爆震波起爆准则和驻定条件,接着对斜爆震波的诱导区结构和波面胞格结构研究进行了总结,随后对斜劈构型对斜爆震波的影响研究现状进行了概述。综述表明,斜爆震波的起爆、驻定和波系结构还需持续开展研究,特别需要关注的是平面斜爆震波的起爆准则和驻定条件,在真实流动条件下更深入研究斜爆震波宏观结构和波面结构的形成机理,探索受限空间内斜爆震波起爆、反射和驻定特性。     

Small Scale Alfvénic Structure in the Aurora

This paper presents a comprehensive review of dispersive Alfvén waves in space and laboratory plasmas. We start with linear properties of Alfvén waves and show how the inclusion of ion gyroradius, parallel electron inertia, and finite frequency effects modify the Alfvén wave properties. Detailed discussions of inertial and kinetic Alfvén waves and their polarizations as well as their relations to drift Alfvén waves are presented. Up to date observations of waves and field parameters deduced from the measurements by Freja, Fast, and other spacecraft are summarized. We also present laboratory measurements of dispersive Alfvén waves, that are of most interest to auroral physics. Electron acceleration by Alfvén waves and possible connections of dispersive Alfvén waves with ionospheric-magnetospheric resonator and global field-line resonances are also reviewed. Theoretical efforts are directed on studies of Alfvén resonance cones, generation of dispersive Alfvén waves, as well their nonlinear interactions with the background plasma and self-interaction. Such topics as the dispersive Alfvén wave ponderomotive force, density cavitation, wave modulation/filamentation, and Alfvén wave self-focusing are reviewed. The nonlinear dispersive Alfvén wave studies also include the formation of vortices and their dynamics as well as chaos in Alfvén wave turbulence. Finally, we present a rigorous evaluation of theoretical and experimental investigations and point out applications and future perspectives of auroral Alfvén wave physics.     

Waves and wave-particle interactions in the magnetosphere: A review

Recent space observations of waves, both electromagnetic and electrostatic, are reviewed and the role which they can play in the dynamics of magnetospheric particles is stressed. Wave particle interactions (WPI) in the exo- and intra-plasmaspheric media depend on the exact process of particle injection under the influence of magnetospheric electric fields, and on the spatial distribution of the cold plasma particles; these two aspects of the problem are studied to some extent. The concepts of optimum cold plasma density, critical energy, limiting flux, marginal stability, steady-state equilibrium are critically discussed. The non-linear aspects — both experimental and theoretical — of WPI's are reviewed and a special section is devoted to active experiments in space. An attempt is made to outline which kind of experiments could be made at high-latitudes, in conjunction with IMS spacecrafts, in order to arrive at a better understanding of magnetospheric processes involving waves and particles.Paper presented at the Esro Symposium on European Sounding Rocket and Scientific Balloon Activity at High Latitudes with Emphasis on the International Magnetospheric Study (Örenäs Slott, Sweden, 1974).     

利用紧致格式捕捉间断的数值方法研究

将通量限制或加权的思想引入到紧致格式中,构造了两类传统方法与紧致格式混合组成的差分格式:通量限制与加权型差分格式。通过方波、组合波、定常激波、非定常Sod问题、Shu问题和Lax问题上的计算,以及与精确解的比较,结果表明这两种方法在间断的捕捉上具有高精度、高分辨率,而在计算方波、组合波或Shu问题和Lax问题上,加权格式具有更大的优势。     

Plasma waves at Venus

Many significant wave phenomena have been discovered at Venus with the plasma wave instrument flow on the Pioneer Venus Orbiter. It has been shown that whistler-mode waves in the magnetosheath of the planet may be an important source of energy for the topside ionosphere. Plasma waves are also associated with thickening of the ionopause current layer. Current-generated waves in plasma clouds may provide anomalous resistance resulting in electron acceleration, possibly producing aurora. Ion-acoustic waves are observed in the bow shock, and appear to be a feature of the magnetotail boundary. Lastly plasma waves have been cited as evidence for lightning on Venus.     

Damping Mechanisms for Oscillations in Solar Prominences

Small amplitude oscillations are a commonly observed feature in prominences/filaments. These oscillations appear to be of local nature, are associated to the fine structure of prominence plasmas, and simultaneous flows and counterflows are also present. The existing observational evidence reveals that small amplitude oscillations, after excited, are damped in short spatial and temporal scales by some as yet not well determined physical mechanism(s). Commonly, these oscillations have been interpreted in terms of linear magnetohydrodynamic (MHD) waves, and this paper reviews the theoretical damping mechanisms that have been recently put forward in order to explain the observed attenuation scales. These mechanisms include thermal effects, through non-adiabatic processes, mass flows, resonant damping in non-uniform media, and partial ionization effects. The relevance of each mechanism is assessed by comparing the spatial and time scales produced by each of them with those obtained from observations. Also, the application of the latest theoretical results to perform prominence seismology is discussed, aiming to determine physical parameters in prominence plasmas that are difficult to measure by direct means.     

The menagerie of geospace plasma waves

Sounding rockets and satellites have discovered a large variety of plasma waves within the Earth's magnetosphere—geospace. These waves are found over a frequency range of millihertz to megahertz. The frequency ranges are generally associated with characteristic frequencies such as the plasma frequency and gyrofrequency. Most waves are generated by hot or streaming magnetospheric plasma; some waves are due to lightning discharges, to intentional man-made transmitters or to incidental radiation from power transmission systems. Propagation of waves from the observation region back to a probable source region can be modelled using ray tracing techniques in a model magnetosphere where the electron number density, ion composition and magnetic field vector is specified. Information in addition to the common amplitude-frequency-time spectrograms can be obtained from the received waves using multiple antennas and receivers. Cross-correlation of the wave electric and magnetic components can provide information on the wave polarization and direction of propagation and on the wave distribution function.     

Ponderomotive Forces in Cosmos

This review is devoted to ponderomotive forces and their importance for the acceleration of charged particles by electromagnetic waves in space plasmas. Ponderomotive forces constitute time-averaged nonlinear forces acting on a media in the presence of oscillating electromagnetic fields. Ponderomotive forces represent a useful analytical tool to describe plasma acceleration. Oscillating electromagnetic fields are also related with dissipative processes, such as heating of particles. Dissipative processes are, however, left outside these discussions. The focus will be entirely on the (conservative) ponderomotive forces acting in space plasmas. The review consists of seven sections. In Section 1, we explain the rational for using the auxiliary ponderomotive forces instead of the fundamental Lorentz force for the study of particle motions in oscillating fields. In Section 2, we present the Abraham, Miller, Lundin–Hultqvist and Barlow ponderomotive forces, and the Bolotovsky–Serov ponderomotive drift. The hydrodynamic, quasi-hydrodynamic, and ‘`test-particle’' approaches are used for the study of ponderomotive wave-particle interaction. The problems of self-consistency and regularization are discussed in Section 3. The model of static balance of forces (Section 4) exemplifies the interplay between thermal, gravitational and ponderomotive forces, but it also introduces a set of useful definitions, dimensionless parameters, etc. We analyze the Alfvén and ion cyclotron waves in static limit with emphasis on the specific distinction between traveling and standing waves. Particular attention has been given to the impact of traveling Alfvén waves on the steady state anabatic wind that blows over the polar regions (Section~5). We demonstrate the existence of a wave-induced cold anabatic wind. We also show that, at a critical point, the ponderomotive acceleration of the wind is a factor of 3 greater than the thermal acceleration. Section 6 demonstrates various manifestations of ponderomotive forces in the Earth's magnetosphere, for instance the ionospheric plasma acceleration and outflow. The polar wind and the auroral density cavities are considered in relation to results from the Freja and Viking satellites. The high-altitude energization and escape of ions is discussed. The ponderomotive anharmonicity of standing Alfvén waves is analyzed from ground based ULF wave measurements. The complexity of the many challenging problems related with plasma processes near the magnetospheric boundaries is discussed in the light of recent Cluster observations. At the end of Section 6, we consider the application of ponderomotive forces to the diversity of phenomena on the Sun, in the interstellar environment, on newborn stars, pulsars and active galaxies. We emphasize the role of forcing of magnetized plasmas in general and ponderomotive forcing in particular, presenting some simple conceivable scenarios for massive outflow and jets from astrophysical objects.     

激波边界层的相互作用对扰动波传播的影响

利用线性稳定性理论和直接数值模拟研究了带有入射斜激波的、来流马赫数Ma=4．5条件下的平板边界层的失稳特性。重点考察了在由于激波边界层相互干扰,平板边界层上形成分离区,又进而产生激波、膨胀波和旋涡等复杂流动现象的流场上游,引入小扰动的TS波后,扰动波传播通过带有这些复杂流动现象的流场时,扰动波的发展变化特点。通过对流场中扰动波（包括基本波和衍生波）演化特征的分析,研究分离和激波等复杂流动现象对平板边界层稳定性的影响特点。数值模拟发现,激波的出现不同于一般的压缩波,在亚声速区与超声速区对扰动波演化的影响是不同的,此外,分离对扰动有稳定作用。     

Radiative damping of gravity waves in the solar atmosphere

The nonlocal character of the radiation field sianificantly modifies the radiative damping of perturbations in the solar photosphere. Gravity waves are not usually considered to exist in the solar photosphere because the radiative damping time, when based on the Newtonian approximation, is too short. However, this restriction does not apply to low order gravity waves. In fact, with the inclusion of nonlocal effects, the radiative damping for low order gravity waves becomes negative for some region in the photosphere and thus acts as a driving mechanism for gravity waves there.     

不规则地形条件下双向DMFT电波传播特性算法研究

 在传统中心差分离散混合傅里叶变换(DMFT)抛物方程模型基础上,针对传统算法计算动态阻抗边界条件时的数值振荡及忽略后向传播与散射造成计算误差增大的问题,提出基于前-后向混合差分方法的递归双向DMFT(TW-DMFT)模型,以一阶前-后向差分方程代替传统的中心差分方程拟合阻抗边界条件,以递归双向传播模型改进传统单向预测模型.仿真分析了双向DMFT模型计算不同边界及媒介条件下单刃峰和实际地形的电波传播分布特性,与传统算法及几何绕射理论(GTD)进行比较,新算法提高稳定性及精度的同时弥补了传统算法的不足,更具有普适性.     

Synthesis of CME-Associated Moreton and EIT Wave Features from MHD Simulations

Soft X-ray (SXR) waves, EIT waves, and Hα Moreton waves are all associated with coronal mass ejections (CMEs). The knowledge of the characteristics about these waves is crucial for the understanding of CMEs, and hence for the space weather researches. MHD numerical simulation is performed, with the consideration of the quiet Sun atmosphere, to investigate the CME/flare processes. On the basis of the numerical results, SXR, EUV, and Hα images of the eruption are synthesized, where SXR waves, EIT waves, and Hα Moreton waves are identified. It confirms that the EIT waves, which border the expanding dimmming region, are produced by the successive opening (or stretching) of the closed magnetic field lines. Hα Moreton waves are found to propagate outward synchronously with the SXR waves, lagging behind the latter spatially by ～27 Mm in the simulated scenario. However, the EIT wave velocity is only a third of the Moreton wave velocity. The synthesized results also suggest that Hα± 0.45Å would be the best off-band for the detection of Hα Moreton waves.     

一种通量加权型紧致格式

将通量加权的思想引入到紧致格式中,构造了一个传统方法与紧致格式混合组成的加权型差分格式.利用该格式与二阶TVD格式分别计算了一维方波、组合波问题和一些黎曼问题,如Sod问题和Shu问题,以及一维定常激波问题.计算结果的比较表明加权格式无论在捕捉各种间断,还是在分辨各种复杂波系上,都具有较大的优势,并与精确解非常吻合.      

超声导波在大型薄铝板缺陷检测中的应用

 为了提高大型薄板超声检测的速度,研究了超声导波及其在大型薄铝板缺陷检测中的应用。推导了超声导波在大型薄铝板中传播的理论模型,分析了导波的波结构,设计并实践了导波检测薄铝板缺陷的方法。试验结果表明,若选取S0导波模式对1 mm薄铝板进行线扫描检测,在有缺陷的地方会出现明显的回波信号。根据缺陷回波与板端回波的传播时间差,可计算出缺陷的位置。缺陷越大,缺陷回波信号幅值越大。选择对缺陷灵敏度高的导波模式,导波法线扫描检测方式可以有效缩短检测时间,提高检测效率。     

Phase coherence of MHD waves in the solar wind

Large amplitude MHD waves are commonly found in the solar wind. Nonlinear interactions between the MHD waves are likely to produce finite correlation among the wave phases. For discussions of various transport processes of energetic particles, it is fundamentally important to determine whether the wave phases are randomly distributed (as assumed in quasi-linear theories) or they have a finite coherence. Using a method based on a surrogate data technique and a fractal analysis, we analyzed Geotail magnetic field data (provided by S. Kokubun and T. Nagai through DARTS at the Institute of Space and Astronautical Science) to evaluate the phase coherence among the MHD waves in the earth's foreshock region. The correlation of wave phases does exist, indicating that the nonlinear interactions between the waves is in progress. This revised version was published online in August 2006 with corrections to the Cover Date.     

关于平面激波在凹两段楔面上的传播

众所周知,当一平面激波同任意形状的障碍物相互作用时,将产生十分复杂的波系,其中激波在曲面壁上的绕射和反射,将产生非定常波系。关于平面激波在凹圆柱壁面上的传播,我们可以用一连串、长度为无限小的楔面所构成的多边形来近似和代替凹圆柱面,因此分析和研究激波在两段楔面上反射和绕射的目的在于得出激波在圆柱壁面以及其它较复杂形状壁面上的传播规律。本文采用马赫-曾德干涉仪在激波管上进行光测模型实验。根据所拍摄的流场干涉图像,以分析其波系的演变过程及传播规律,得到有关流场的密度分布和压力分布,更为重要的是给出流场参数的定量结果。