Drift motion of domain boundaries in garnet ferrites in an acoustic wave field

The drift motion of a 180° domain boundary in garnet ferrites with two nonequivalent sublattices is studied in an elastic stress field induced by an acoustic wave propagating in the domain boundary plane. The dependences of the drift velocity on the amplitude and polarization of the acoustic wave are obtained, and the drift motion conditions for a strip domain structure are determined.     

Amplification of an acoustic wave in inhomogeneous Piezoelectric semiconductors

The theory of the amplification of an acoustic wave in an inhomogeneous piezoelectric semiconductor in the presence of a transverse magnetostatic field is developed assuming the explicit dependence of the relaxation time (τ) on the position coordinate. It is found that the implication of the sound wave is possible even if the drift velocity of the electron is smaller than the velocity of sound in the medium.     

Frequency dependence of the amplitude of domain-wall oscillations in an acoustic wave field

The velocity of oscillatory motion of domain walls is investigated as a function of the parameters of a magnetic material and an external acoustic field. The dependence of the amplitude of domain-wall oscillations on the frequency of an external acoustic wave is determined. It is found that this dependence exhibits a resonant behavior.     

Computer simulation of the drift of solid particles caused by resonance gas oscillations in the open channel

Computer simulation methods are used to study the drift of solid spherical particles suspended in the open channel due to longitudinal oscillations of the gas column. The gas velocity field consists of periodic nonlinear waves and an acoustic flow. The particles move under the action of the Stokes force. Particle distributions in the wave field of the open channel are obtained in the vicinity of the first, second and third eigen-frequencies of the gas column. The particle’s spatial distribution features attributed to the particle’s drift under the action of acoustic radiation are revealed.     

Electrostatic instability in magnetically confined inhomogeneous plasma driven by nonlinear force

A theoretical investigation on amplification of electrostatic ion acoustic wave in magnetically confined plasma has been presented in this paper. This investigation considers nonlinear wave–particle interaction process, called plasma maser effect, in presence of drift wave turbulence supported by magnetically confined inhomogeneous plasma. The role of associated nonlinear dissipative force in this effect in a confined plasma has been analyzed. The nonlinear force, which arises as a result of resonant interaction between electrons and modulated fields, is shown to drive the instability. Using the ion fluid equation and the ion equation of continuity, the nonlinear dispersion relation of a test ion acoustic wave has been derived, and the growth rate of ion acoustic wave in presence of low frequency drift wave turbulence has been estimated using Helimak data.     

水下涡流场前向声散射特性分析

研究水下涡声散射特性,在目标探测和流场声成像领域具有重要意义。针对水下低马赫数涡流场前向声散射建立了数值计算方法,探究了其形态函数和指向性。首先,基于摄动声学理论给出了考虑流声耦合作用的涡声散射模型,采用时域有限差分结合完美匹配层构建了数值求解方法;随后,在算法验证的基础上,预报分析了高斯涡涡核尺寸在1~10 m,同时入射平面波无量纲波数在1~10范围内,涡流场强度对前向声散射特性的影响。结果表明,低马赫数下,声散射场具有对称性,且有明显的主瓣和指向性。其前向散射形态函数随入射波波数、涡核尺寸、涡流场强度增加而增大;主瓣方位角随波数增加而趋近入射波传播方向。      

Nonlinear dynamics of a domain wall in the field of a sound wave propagating in the plane of the wall

A theoretical model is proposed for describing the drift of a 180° domain wall in a weak ferromagnet in the field of elastic stresses produced by a strong sound wave propagating in the plane of the wall. The dependence of the drift velocity on the frequency, amplitude, and polarization of the sound wave is found. It is predicted that drift of a striped domain structure is possible.     

A braking drift current on the slopes of wind waves in an amplification zone

A drift current was experimentally studied on the slopes of wind waves in an amplification zone. It was found that the drift decreases proportionally to the wave steepness at the front wave slope. We tested a hypothesis that relates the decrease in the drift velocity at the front wave slope with the formation of vortices in a viscous air layer. A physical model of the event and a method for the calculation of the drift decrease at the front wave slope in an amplification zone are suggested. The model calculations agree well with experimental data within the measurement error, which is less than 10% of the measured value.     

Modelling the pressure field in the vicinity of a microphone membrane using PIV

A new approach for estimating the acoustic pressure in the near field of a microphone based on non-intrusive direct measurement of acoustic particle velocity is proposed.This method enables the estimation of the acoustic pressure inside a domain located in front of the microphone membrane. The acoustic pressure is calculated using the acoustic particle velocity on the frontiers of this domain and a physical model based on the Green function of the system.Results are obtained using the acoustic velocity measured with Particle Image Velocimetry (PIV) in front of a microphone excited with a plane wave inside a rectangular waveguide. They show that the diffraction of the plane wave by the microphone leads to an increase of the acoustic pressure on the microphone edge in the order of magnitude of 0.1 dB.     

Acoustic-electromagnetic slow waves in a periodical defective piezoelectric slab

Coupled slow waves, slow acoustic waves, and electromagnetic waves are simultaneously achieved based on a piezoelectric material, in which a line defect is created within a honeycomb lattice array of cylindrical holes etched in a LiNbO_3 slab. Finite element simulations in frequency domain and time domain demonstrate that a highly localized slow mode is obtained in the defect. Owing to the piezoelectricity of LiNbO_3, acoustic and electromagnetic waves are coupled with each other and transmit along the line defect. Therefore, in addition to a slow acoustic wave, an electromagnetic wave with a group velocity even lower than conventional acoustic waves is achieved.     

Drift ion acoustic solitons in an inhomogeneous 2-D quantum magnetoplasma

Linear and nonlinear propagation characteristics of quantum drift ion acoustic waves are investigated in an inhomogeneous two-dimensional plasma employing the quantum hydrodynamic (QHD) model. In this regard, the dispersion relation of the drift ion acoustic waves is derived and limiting cases are discussed. In order to study the drift ion acoustic solitons, nonlinear quantum Kadomstev-Petviashvilli (KP) equation in an inhomogeneous quantum plasma is derived using the drift approximation. The solution of quantum KP equation using the tangent hyperbolic (tanh) method is also presented. The variation of the soliton with the quantum Bohm potential, the ratio of drift to soliton velocity in the co-moving frame, , and the increasing magnetic field are also investigated. It is found that the increasing number density decreases the amplitude of the soliton. It is also shown that the fast drift soliton (i.e., v_*>u) decreases whereas the slow drift soliton (i.e., v_*<u) increases the amplitude of the soliton. Finally, it is shown that the increasing magnetic field increases the amplitude of the quantum drift ion acoustic soliton. The stability of the quantum KP equation is also investigated. The relevance of the present investigation in dense astrophysical environments is also pointed out.     

Propagation of terahertz waves in a dust acoustic wave

The propagation of terahertz waves in a dust acoustic wave is investigated numerically. By assuming a sinus profile of the dust number density in the dust acoustic waves, the transmission properties are calculated using finite difference time domain method. It shows that the dust acoustic wave can function similarly as a Bragg filter to block the terahertz waves of a certain wavelength. The bandwidth of the filter depends on the density profile of the dust acoustic wave.     

Effective mass of an electron in an electromagnetic field

The effective-mass formalism is shown capable to describe the fully relativistic motion of an electron in a strong, locally plane, electromagnetic wave, determining the drift caused by the wave inhomogeneity and by additional weaker fields. The limits of this approach are discussed, in connection with the occurrence of resonances.     

Amplification and drift-related nonreciprocity of the shear wave scattering by a semiconductor cylinder in a piezoelectric

The scattering of a plane monochromatic shear wave by a circular semiconductor cylinder soldered into a piezoelectric of class 6mm(4mm, ∞m) is considered for the case when an azimuth drift current occurs in the cylinder. It is found that the drift-related nonequivalence of scattering in opposite azimuth directions of wave propagation around the cylinder is the origin of the asymmetry of the polar scattering pattern while the effective (for the partial waves travelling around the cylinder in the drift direction with a sufficiently high angular velocity) acoustoelectronic amplification reduces the total scattering loss and can make it negative. A relatively strong contribution of the plasma and drift to the scattering is predicted for the case of acoustic matching between the materials of the cylinder and the surrounding piezoelectric.     

Invariance of the Transmission Function of an Acousto-Optic Device for a Change in the Drift Angle of an Acoustic Beam

Acoustical Physics - Abstract—It is shown that the transmission function of an acousto-optic device remains unchanged for variations in the acoustic drift angle and acoustic column width when...     

Dynamics of domain walls in pattern formation with traveling-wave forcing

We study dynamics of domain walls in pattern forming systems that are externally forced by a moving space-periodic modulation close to 2:1 spatial resonance. The motion of the forcing induces nongradient dynamics, while the wave number mismatch breaks explicitly the chiral symmetry of the domain walls. The combination of both effects yields an imperfect nonequilibrium Ising-Bloch bifurcation, where all kinks (including the Ising-like one) drift. Kink velocities and interactions are studied within the generic amplitude equation. For nonzero mismatch, a transition to traveling bound kink-antikink pairs and chaotic wave trains occurs.     

Drift velocity in an amplification zone of wind waves

Drift wind flow in the amplification zone of a wind wave is investigated experimentally. It is found that the wind drift diminishes in proportion to the wave steepness on the forward slope of a wave in the region of a water surface deformed by vortices in a viscous layer of air. Vortices delaying the drift are found in the viscous layer on the back slope of a wave where the shift velocity of water diminishes.     

Vortices in an anisotropic plasma

Localized electrostatic nonlinear drift wave structures in a plasma with hot electrons and anisotropic ions are considered. The anisotropic energy distribution leads to a new nonlinearity in the evolution equation of finite amplitude drift waves. One- and two-dimensional solutions of physical interest are presented.     

Diffraction of sound pulses on an elastic spherical shell submerged in an oceanic waveguide

The paper is devoted to simulating an acoustic field scattered by an elastic spherical shell placed in a waveguide with a fluid attenuating bottom. The emitted signal is a wideband pulse with a Gaussian envelope. The normal wave method is used in the frequency domain for calculating the field of a point source in a free waveguide and the shell scattering coefficients. Movement of the receiver along a vertical straight line located behind the shell makes it possible to obtain a “three-dimensional” image of the field scattered by the shell. In this representation, the horizontal axis is time; the vertical axis is the submersion depth of the receiver; the intensity shows the amplitude of the received signal. Such three-dimensional structures make it possible to analyze the dependence of the complex diffraction structure of the acoustic field on receiver depth. In the considered numerical example, a thin, elastic, spherical shell is located near the attenuating fluid bottom.     

Comparison of an integral equation on energy and the ray-tracing technique in room acoustics

This paper deals with a comparison of two room acoustic models. The first one is an integral formulation stemming from power balance and the second is the ray-tracing technique with a perfectly diffuse reflection law. The common assumptions to both models are the uncorrelated wave hypothesis and the perfectly diffuse reflection law. The latter allows the use of these methods for nondiffuse fields beyond the validity domain of Sabine's formula. Comparisons of numerical simulations performed with the softwares RAYON and CeReS point out that these results are close to each other and finally, a formal proof is proposed showing that both methods are actually equivalent.