Propagation of Fast Magnetoacoustic Waves in Stratified Solar Atmosphere

The characteristics of magnetohydrodynamic fast wave propagation in the solar stratified atmosphere are studied by the ray tracing method. The propagation behaviour of the wavefronts is described in detail. A magnetic field incorporating the characteristics field spreading expected in flux tubes is used, which represents the main feature of an active region. Partly ionization is considered beside the stratified solar atmosphere consisting chromosphere, transition region and corona. The study may explain the characteristics in observations of Moreton and extraultraviolet image telescope （EIT） waves. The wavefront incurred by the disturbance initialized at the base of the transition region propagates fast initially due to strong magnetic field, and it slows down when arriving beyond the region of flux-tube. Meanwhile, the wave propagates in the corona with a more consistent speed, as seen in the observation of EIT waves. The speeds and propagated characteristics in chromosphere and corona of the wavefronts are in agreement with those observed in H~ Moreton and EIT waves, respectively.     

Nonlinear Electrostatic Ion‐Acoustic Waves in the Solar Atmosphere

Basing on recent solar models, the excitation of ion‐acoustic turbulence in the weakly‐collisional, fully and partially‐ionized regions of the solar atmosphere is investigated. Within the frame of hydrodynamics, conditions are found under which the heating of the plasma by ion‐acoustic type waves is more effective than the Joule heating. Taking into account wave and Joule heating effects, a nonlinear differential equation is derived, which describes the evolution of nonlinear ion‐acoustic waves in the collisional plasma.     

Propagation Characteristics of Infrared Pulse Waves through Windblown Sand and Dust Atmosphere

The physics characteristics of the windblown sand and dust atmosphere at the sand bench of Yellow River in China are discussed. The pulse distortion and time delay of infrared nanosecond pulse propagating through the atmosphere having sand and dust particles are investigated at 1.06 and 3.8 μm, respectively. It is shown that the delay of 10 ns laser pulse propagating through 5 km windblown sand and dust atmosphere are over 1 ns and 10 ns at 1.06 and 3.8 μm, respectively. The pulse spread increases slightly with wavelength increase. The pulse spread of a 10 ns laser pulse is over 40 ns at 3.8 μm. The pulse delay and spread increase rapidly with the sand particle density increasing in atmosphere. The narrower the pulse width is, the more the pulse distortion is. Hence, at infrared band, for a laser pulse propagating in sand and dust atmosphere, the pulse delay and spread are quite severe and need be taken into account for a narrower pulse laser system.     

On the Possibility of Reflectionless Propagation of Plane Acoustic Waves in Continuously Stratified Media

Acoustical Physics - The example of vertical propagation of acoustic plane waves in the atmosphere is used to establish that the reflectionless propagation of acoustic waves occurs only in...     

Non-Reflective Magnetohydrodynamic Waves in an Inhomogeneous Plasma

Radiophysics and Quantum Electronics - The existence of traveling waves in a strongly inhomogeneous magnetized plasma is studied. It is shown that under certain conditions for characteristics of...     

Erratum to: On the Possibility of Reflectionless Propagation of Plane Acoustic Waves in Continuously Stratified Media

Acoustical Physics - An Erratum to this paper has been published: https://doi.org/10.1134/S1063771022340024     

An Investigation of the Effects of Internal Waves on Sound Propagation in a Stratified Medium with a Sloping Bed

Internal waves usually cause temporal and spatial changes of density and consequently affect the acoustic wave propagation in the ocean. The purpose of this study is a laboratory investigation of the effects of internal waves generated by oscillation of a cylinder in a large stratified glass tank with a sloping bed on the sound waves propagation. Results showed that sound waves are affected by internal waves that depend on the slope angle to the direction of internal wave propagation angle ratio. When the ratio is subcritical or supercritical, the acoustic signal is much reduced as compared to the case with no sloped bottom. This can be explained in terms of the internal waves energy reaching the sloped bed and their reflections.     

Influence of Magnetic-Field and Plasma-Density Inhomogeneities on the Propagation and Amplification of Radio Waves in the Solar Corona

We analyze the maser generation of millisecond spikes of the solar radio emission at the cyclotron resonance of a fast extraordinary wave in an inhomogeneous medium. It is shown that the magnetic-field inhomogeneity with parameters typical of the solar corona drastically reduces the time of electromagnetic-wave amplification, which is explained by the fact that these waves leave the resonance region in the wave-vector space. As a result, an unstable electron distribution can be formed. The efficient generation of radiation becomes possible only in such local regions where the influence of the magnetic-field inhomogeneity is compensated by small-scale inhomogeneities of the plasma density with typical scales ranging from tens to hundreds of kilometers. Taking the effect of inhomogeneous medium into account allows us to explain spatial and temporal characteristics of the spikes.     

Small BGK Waves and Nonlinear Landau Damping

Consider a 1D Vlasov-poisson system with a fixed ion background and periodic condition on the space variable. First, we show that for general homogeneous equilibria, within any small neighborhood in the Sobolev space ${W^{s,p}\left( p >1 ,s <1 +\frac{1}{p}\right)}${W^{s,p}\left( p >1 ,s <1 +\frac{1}{p}\right)} of the steady distribution function, there exist nontrivial travelling wave solutions (BGK waves) with arbitrary minimal period and traveling speed. This implies that nonlinear Landau damping is not true in W^s,p( s < 1 +\frac1p){W^{s,p}\left( s <1 +\frac{1}{p}\right)} space for any homogeneous equilibria and any spatial period. Indeed, in a W^s,p(s < 1 +\frac1p){W^{s,p}\left(s <1 +\frac{1}{p}\right)} neighborhood of any homogeneous state, the long time dynamics is very rich, including travelling BGK waves, unstable homogeneous states and their possible invariant manifolds. Second, it is shown that for homogeneous equilibria satisfying Penrose’s linear stability condition, there exist no nontrivial travelling BGK waves and unstable homogeneous states in some ${W^{s,p}\left( p >1 ,s >1 +\frac{1}{p}\right)}${W^{s,p}\left( p >1 ,s >1 +\frac{1}{p}\right)} neighborhood. Furthermore, when p = 2, we prove that there exist no nontrivial invariant structures in the ${H^{s}\left( s > \frac{3}{2}\right) }${H^{s}\left( s > \frac{3}{2}\right) } neighborhood of stable homogeneous states. These results suggest the long time dynamics in the ${W^{s,p}\left( s >1 +\frac{1}{p}\right) }${W^{s,p}\left( s >1 +\frac{1}{p}\right) } and particularly, in the ${H^{s}\left( s > \frac{3}{2}\right) }${H^{s}\left( s > \frac{3}{2}\right) } neighborhoods of a stable homogeneous state might be relatively simple. We also demonstrate that linear damping holds for initial perturbations in very rough spaces, for a linearly stable homogeneous state. This suggests that the contrasting dynamics in W ^{s, p} spaces with the critical power s=1+\frac1p{s=1+\frac{1}{p}} is a truly nonlinear phenomena which can not be traced back to the linear level.     

Transverse Wave Propagation in Relativistic Two-Fluid Plasmas around Schwarzschild-de Sitter Black Hole

We investigate transverse electromagnetic waves propagating in a plasma influenced by the gravitational field of the Schwarzschild-de Sitter black hole. Applying 3+1 spacetime split we derive the relativistic two-fluid equations to take account of gravitational effects due to the event horizon and describe the set of simultaneous linear equations for the perturbations. We use a local approximation to investigate the one-dimensional radial propagation of Alfvén and high frequency electromagnetic waves. We derive the dispersion relation for these waves and solve it for the wave number k numerically.     

慢布拉格类孤子的传播特性

在耦合模理论的基础上，分析了线性周期结构的色散关系，给出了一维无限长的克尔类非线性介质周期结构中的慢布拉格类孤子解。并且指出，增加脉冲能量会导致群速度色散效应增强，在非线性作用下，禁带宽度会变小，波的频率也会发生偏移，其偏移量主要取决于失谐因子、传播速度、波振幅强度以及非线性系数等参量。     

Stationary Propagation of Coupled Nonlinear High Frequency Waves and Ion-Acoustic Waves in a Plasma

Stationary solutions of the coupled equations for high frequency transverse waves in a plasma and for the low frequency ion motion (T_e?T_i) are investigated numerically. The use of the nonlinear hydrodynamic equations instead of the linear wave equation for ion acoustic waves allows to look for solutions without restrictions of the Mach number M = V/c_s (V group velocity, c_s ion acoustic velocity) and the ratio ω/ω_pe (ω frequency of the HF-field, ω_pe electron plasma frequency at the undisturbed region). In particular, supersonic soliton-like solutions with n/n_o > 1 were found. Dispersion effects due to charge separation are not included.     

Mode Structures and Damping of Quantized Spin Waves in Ferromagnetic Nanowires

Magnonic devices based on spin waves are considered as a new generation of energy-efficient and high-speed devices for storage and processing of information. Here we experimentally demonstrate that three distinct dominated magneto-dynamic modes are excited simultaneously and coexist in a transversely magnetized ferromagnetic wire by the ferromagnetic resonance(FMR) technique. Besides the uniform FMR mode, the spin-wave well mode, the backward volume magnetostatic spin-wave mode, and the perpendi...     

涡旋光束在湍流大气中的传输特性

根据广义的惠更斯-菲涅耳原理, 研究了涡旋光束在湍流大气中的传输特性。研究结果表明, 涡旋光束在湍流大气中传输时, 截面光强会从空心分布转化为高斯分布。光束所带的拓扑电荷数以及大气湍流均会影响光强分布的变化。研究结果还表明, 涡旋光束能够抑制大气湍流对光束扩展的影响, 这一现象得到了实验上的证实。通过杨氏双缝干涉的方法, 还研究了涡旋光束经过湍流大气传输后的拓扑电荷数。研究发现, 涡旋光束经过湍流大气后, 拓扑电荷数将发生波动。     

Propagation of Four-Petal Gaussian Beams in Turbulent Atmosphere

An analytical expression for the average intensity of four-petal Gaussian beams in turbulent atmosphere is derived. Studies show that in turbulent atmosphere, the contour lines of four-petal Gaussian beams with lower order N evolve into a number of petals with the increase in propagation distance, the contour lines with higher order N can reserve four-petal distribution at longer propagation distance than that with lower order N. These properties are similar to those in free space. However, with further increases of the propagation distance, the contours lines in turbulent atmosphere are different from those in free space.     

Propagation of Electromagnetic Waves in Cholesteric Liquid Crystals

Russian Physics Journal - Fundamental properties of solutions of Maxwell’s equations describing the propagation of electromagnetic waves in a cholesteric liquid crystal with tensor...     

利用受激布里渊散射效应补偿激光大气传输过程中的畸变

提出了利用受激布里渊散射的阈值效应主动在非配合,扩展目标上实现小面积信标的方法,在不同的大气扰动条件（Cn^2=10^-16--10^-12)下,对激光的远距离（10km)补偿传输过程进行了模拟计算,获得了到达目标上的相位共轭光的光强分布。分别在不同的实验环境进行了激光补偿传输实验,其中激光补偿传输距离最远达到250m。实验结果证实了利用受激布里渊散射实现激光大气传输补偿的有效性,证明利用阈值效应在目标上主动获得小面积信标的方法是可行的。