On formulation of a transition matrix for electroporoelastic medium and application to analysis of scattered electroseismic wave

On the basis of Pride's theory (1994) which couples Biot's theory for poroelastic medium (1956) and Maxwell equations via flux/force transport equations, we extend Yeh et al. (2004) approach for poroelastic medium to develop a transition matrix for electroporoelastic medium. The transition matrix, which relates the coefficients of scattered waves to those of incident waves, is then derived through the application of Betti's third identity and the associated orthogonality conditions for the electroporoelastic medium. To illustrate the application, a simple case of the scattering problem of a spherical electroporoelastic inclusion, embedded within the surrounding electroporoelastic medium subjected to an incident plane compressional wave is considered.     

Theoretical estimates of radial electric fields and plasma rotation induced in H-1NF by RF waves

The purpose of this study is to estimate, for planned experiments at the H-1NF heliac, nonlinear variations of the stationary radial electric field, and poloidal and toroidal plasma rotation, that result from ponderomotive forces exerted by large amplitude RF waves in the H-1NF. Similarly as in the previous studies of nonlinear transport effects induced by RF waves, the nonlinear ponderomotive force effects on the radial electric field, toroidal and poloidal plasma rotation become important for dissipated powers of the order of 1 MWm^–3 for RF waves with frequency of about 10 MHz. At these high RF powers, the nonlinear ponderomotive force effects might therefore result in important changes in plasma confinement and RF wave coupling in H-1NF.This work has been partially supported by the Australian National University, by the DIST Department of the Australian Government, by the Czech Grant Agency grants No. 202/96/1355 and 1350, and by the Queen Elisabeth II grant administered by G.G. Borg. The author is grateful to G.G. Borg and R.L. Dewar for many stimulating discussions.     

Generation of zonal magnetic fields by drift waves in a current carrying nonuniform magnetoplasma

It is shown that zonal magnetic fields (ZMFs) can be nonlinearly excited by incoherent drift waves (DWs) in a current carrying nonuniform magnetoplasma. The dynamics of incoherent DWs in the presence of ZMFs is governed by a wave-kinetic equation. The governing equation for ZMFs in the presence of nonlinear advection force of the DWs is obtained from the parallel component of the electron momentum equation and the Faraday law. Standard techniques are used to derive a nonlinear dispersion relation, which depicts instability via which ZMFs are excited in plasmas. ZMFs may inhibit the turbulent cross-field particle and energy transport in a nonuniform magnetoplasma.     

Forces exerted on atoms by stochastic laser fields

We present analytical results and numerical simulations for the force exerted on moving atoms in the fields of two counterpropagating waves whose amplitudes or phases are described as stochastic processes. We assume that one field repeats the other with some delay, as would occur when the two fields derive from a common source through a beam splitter and mirrors. We show that, just as with the force exerted by the field of two counterpropagating sequences of π-pulses, or two counterpropagating bichromatic or frequency-modulated waves, the force on an atom in counterpropagating stochastic waves may considerably exceed the force exerted by the field of a single running wave. For comparison we also discuss the interaction of an atom with two counterpropagating waves when one of them is monochromatic and the other one has a stochastic phase. In this case the force substantially exceeds the force exerted by the field of a single running wave but appreciably smaller then the radiative force in the counterpropagating waves in which one field repeats the other with some delay.     

The propagation of infinitesimal disturbances in an ultrarelativistic gas according to the method of elementary solutions

It has recently been shown that a linearized relativistic BGK model can be reduced, in the ultrarelativistic limit, to a system of three uncoupled transport equations for thermal, sound, and shear waves. The equation describing the propagation of thermal waves is the well-known one-speed neutron transport with isotropic scattering in the conservative case. In this paper the solution of the half-space problem for the equation describing the propagation of shear and sound waves is given according to Case's elementary solutions method.     

Ion larmour radius effect on rf ponderomotive forces and induced poloidal flow in tokamak plasmas

Analytical approximations are used to clarify the effect of Larmour radius on rf ponderomotive forces and on poloidal flows induced by them in tokamak plasmas. The electromagnetic force is expressed as a sum of a gradient part and of a wave momentum transfer force, which is proportional to wave dissipation. The first part, called the gradient electromagnetic stress force, is combined with fluid dynamic (Reynolds) stress force, and gyroviscosity is included into viscosity force to model finite ion Larmour radius effects in the momentum response to the rf fields in plasmas. The expressions for the relative magnitude of different forces for kinetic Alfven waves and fast waves are derived.     

Effects of polarization force and nonthermal ions on dust-acoustic (DA) shock waves in a strongly coupled dusty plasma with positively charged dust

The nonlinear propagation of the dust-acoustic (DA) waves in a strongly coupled dusty plasma containing Maxwellian electrons, nonthermal ions, and positively charged dust is theoritically investigated by a Burgers equation. The effects of the polarization force (which arises due to the interaction between electrons and highly positively charged dust grains) and nonthermal ions are studied. DA shock waves are found to exist with positive potential only. It represents that the strong correlation among the charged dust grains is a source of dissipation, and is responsible for the formation of DA shock waves. The effects of polarization force and nonthermal ions significantly modified the basic features of DA shock waves in strongly coupled dusty plasma.     

分数阶对数耦合系统在非周期外力作用下的定向输运现象

本文讨论了分数阶对数耦合系统在非周期外力作用情况下, 耦合粒子链的定向输运现象. 由于粒子在黏性介质中的运动具有“记忆性”, 所以本文通过将系统建模为分数阶对数耦合模型来研究各个系统参数对粒子链运动状态的影响. 数值仿真表明: 1)对于此类系统, 只有在存在外力作用的情况下粒子链才能够产生定向输运现象, 并且粒子链平均流速随着外力的增大而增大. 2)对于分数阶阶数较小的系统, 阻尼记忆性对粒子链的运动状态有显著的影响, 具体表现为: 粒子链的平均流速存在上界(这个上界非常小), 无论外力、耦合力以及噪声强度如何变化, 粒子链的平均流速都不会超过这个上界. 当系统的阻尼力很大且外力为零时, 粒子链不会产生定向输运现象. 3) 当系统的阶数与外力较大时, 虽然粒子链能够产生定向流, 但是此时系统对耦合力与噪声具有免疫性. 4) 耦合力与噪声强度对粒子链运动的影响只在外力较小的情况下有所表现. 在这种情况下, 当系统阶数充分大时, 粒子链的平均流速随着耦合力与噪声强度的变化而变化, 并且伴随着定向流的产生.     

Unpinning the spiral waves by using parameter waves

The spiral waves anchored to heterogeneous areas are more difficult to control and eliminate than freely rotating ones in homogenous mediums. To eliminate pinned spiral waves, the resistant force should be provided to resist the pinning force. Other than advection field, we introduce parametric wave to play the role of providing resistant force. It is found that the parametric wave with large enough amplitude and proper frequency can unpin and eliminate the spiral wave successfully. The capability of parametric wave in providing resistant force is dependent on its amplitude and frequency sensitively. On the basis of parametric wave, the dependence of pinning force on the size and level of heterogeneity is further confirmed.     

Influence of ultrasonic surface acoustic waves. on local friction studied by lateral force microscopy

We studied dynamic friction phenomena introduced by ultrasonic surface acoustic waves using a scanning force microscope in the lateral force mode and a scanning acoustic force microscope. An effect of friction reduction was found when applying surface acoustic waves to the micro-mechanical tip-sample contact. Employing standing acoustic wave fields, the wave amplitude dependent friction variation can be visualized within a microscopic area. At higher wave amplitudes, a regime was found where friction vanishes completely. This behavior is explained by the mechanical diode effect, where the tip's rest position is shifted away from the surface in response to ultrasonic waves.     

Reconfigurable topological phononic crystal slabs

We propose two-dimensional reconfigurable phononic crystal slabs that support topologically protected edge states for Lamb waves. It consists of a triangular lattice of triangular-like air holes perforated in a slab and two sandwich cylinders are placed in the matrix of each unit cell. The pseudospin–orbit coupling is achieved by shifting the sandwich cylinders up or down. The robust transport of Lamb waves along reconfigurable interfaces is further demonstrated. The dynamically reconfigurable design provides an excellent platform for tuning the frequency range of topological edge states and steering efficient transport of Lamb waves along arbitrary pathways, which can be employed for elastic-wave communications, signal processing, and sensing.     

Chaotic transport across two-dimensional jet streams

A dynamically consistent model of a jet stream modulated by Rossby waves is used to analyze the onset of chaotic transport of a passive tracer across the jet (cross-jet transport). For odd Rossby wavenumbers, a technique is developed to find a central invariant curve whose breakup signifies the onset of cross-jet transport. Amplitude and resonance mechanisms of breakup of this curve are investigated. For even-odd pairs of wavenumbers, an alternative technique is proposed for detecting cross-jet transport, based on an overlap of northern and southern stochastic layers. In this case, the Rossby-wave amplitudes required for global crossjet transport to occur are larger than those in the case of odd wavenumbers. The predicted results should be tested in laboratory experiments simulating jet streams modulated by Rossby waves.     

有完整Coriolis力和热源影响下超长波的解析解

利用修正的Burger模式,采用行波解和泰勒级数展开法得到有完整Coriolis力和热源影响下超长波的解析解.得到描述非线性超长波的KdV和KdV-mKdV方程,并得到它的椭圆余弦波解、孤立波解和三角函数周期解.     

Accumulation of dwell times in light diffusion

We discuss various speeds of propagation that are relevant for the dynamics of classical waves in random media: phase velocity, group velocity and transport velocity. The transport velocity can be much smaller than the phase velocity due to the long dwelling of classical waves inside resonant scatterers. We show that the transport velocity of light can be obtained experimentally by study both transient and steady-state diffusion of light.     

Solitary deflection waves on the supersonic domain wall in yttrium orthoferrite

The moving antiferromagnetic vortices are accompanied by solitary deflection waves. These waves allow to investigate generation and nonlinear dynamics of the antiferromagnetic vortices on the moving domain wall with the help of the two- and three-fold digital high speed photography. On the quasi-relativistic domain wall the vortex dynamics is quasi-relativistic with the limiting velocity c=20 km/s, which is equal to the spin-wave velocity. The solitary deflection waves dynamics can be explained assuming existence of the gyroscopic force. A theory for the gyroscopic force in the orthoferrite domain wall is elaborating by A.K. Zvezdin et al. currently. We present a comparison of the theoretical and experimental results on the dynamics of the solitary deflection waves, which accompany the antiferromagnetic vortices in the domain wall of orthoferrites.     

Faster-than-light particles: An alternative view

The existence of a wave motion analogous to the electromagnetic waves, but with wave velocity less than that of light, is postulated. It is suggested that these waves, which transport energy and momentum with subluminal velocities, could replace the concept of faster-than-light particles. The possibility of the neutrinos as being the source of the waves is suggested for further investigation.     

Lévy噪声与周期力共同驱动下的螺旋波动力学

研究加性Lévy噪声与周期外力对FitzHugh-Nagumo可激系统中螺旋波动力学行为的影响.螺旋波波头的运动随外力周期在一定范围内呈规则变化,该规则变化可用相应的傅立叶谱理解,维持该规则变化的是锁频行为.Lévy噪声序列中包含着小概率的大尺度噪声,螺旋波波头运动改变主要来自于它们的影响,本文指出Lévy噪声对波头运动的影响也依赖于外力周期的取值.在适当的参数取值下,Lévy噪声的存在也能导致螺旋波的消失,这为螺旋波的控制、消除提供了一种方法.分析了系统周期与外力周期的锁定行为,给出了不同噪声强度下的Arnold舌,指出随机共振行为的存在.     

Wave-induced bed flows by a Lagrangian vortex scheme

Nominally 2-dimensional viscous flow induced by gravity waves over a spatially periodic bed is simulated by a Lagrangian vortex scheme. A vortex sheet is introduced on the surface at each time step to satisfy the zero velocity conditions. The sheet is discretised; the vortex-in-cell method is used to convect vorticity and random walks are added to effect viscous diffusion. Good agreement with analytical theory is obtained for velocity profiles in uniform sinusoidal flow and for mass transport due to linear waves. Mass transport for finite amplitude waves is also obtained. For separated flow over rippled beds, which is still liminar, a vortex decay factor is required to produce agreement with experiment and is thought to compensate for large scale 3-dimensional effects.     

Noncontact transportation in water using ultrasonic traveling waves

A noncontact transport experiment in water using ultrasonic traveling waves was investigated. Acrylic, aluminum, and brass discs were used as test objects. Traveling waves were generated using two ultrasonic transducers attached at the ends of a vibrating plate. One side was used as the wave-source side and the other side was used as the wave-receiving side. Acrylic plates cemented to the sides of the vibrating plate formed a tank to hold water. Object transportation was accomplished by adding a small amount of water to the vibrating structure. The transport velocity of floating objects in water is faster than for floating transport in air because of buoyancy. The transport velocity of an object depends on water height. The minimum value of the velocity occurs when the disc thickness is equal to the water height. The transport velocity increases as the height of water increases. For very shallow depths, the largest velocity is obtained when cavitation-induced streaming occurs.