The radiation of elastic waves from a localized source is observed experimentally in a two-dimensional plasma crystal. An initial shear stress applied by a laser forms a small dipole source. The emerging complex wave pattern is shown to consist of outgoing compressional and shear wave pulses. Subsequent structures are identified as inward-going waves due to the finite size of the source region,...

Emission of compressional acoustic waves at the second harmonic frequency (second harmonic generation, SHG) is possible from rough surfaces undergoing oscillatory shear in liquids. This nonlinear response is a consequence of the inertial term in the Navier-Stokes equation. On a corrugated surface, the streamlines of the sheared liquid are not strictly parallel to the surface, leading to variati...

The time harmonic Green function for a point load in an unbounded fluid-saturated porous solid is derived in the context of Biot's theory. The solution contains the two compressional waves and one transverse wave that are predicted by the theory and have been observed in experiments. At low frequency, the slow compressional wave is diffusive and only the fast compressional nd transverse waves r...

A novel method for the excitation of ELF waves in the ionosphere is presented. It utilizes the nonlinear mixing of two groundor satellite-produced radio frequency waves with a compressional Alfv6n wave. Parametric amplification thresholds are estimated to be between 10 and 20 MW peak power for 5-MHz pumps producing waves in the ELF range. Potential applications to ELF communications are discussed.

Although synthetic borehole seismograms routinely can be computed for a wide range of borehole conditions, the physical nature of shear and compressional head waves in fluid-filled boreholes is poorly understood. This paper presents a series of numerical experiments designed to provide insight into the physical mechanisms controlling head wave propagation in boreholes. These calculations demons...

The radiation patterns of an elastic wave field generated by circular plane compressional and shear transducers are derived using the method of steepest descent. These patterns contain both effects of the elastic half space and the amplitude modulation due to the finite dimension of the piston source. Behaviors of radiation patterns of the generated compressional and shear waves are shown for l...

Wakes composed of compressional and shear waves were studied experimentally in a two-dimensional screened-Coulomb crystal. Highly charged microspheres suspended in a plasma settled in a horizontal monolayer and arranged in a triangular lattice with a repulsive interparticle potential. Wakes were excited by a moving spot of Ar+ laser light. Depending on the laser spot speed, compressional waves ...

Compressional pulses were launched in a two-dimensional Yukawa lattice, a hexagonal monolayer of polymer microspheres suspended in a plasma. The pulsed wave was excited by a laser beam, and nonlinear effects were observed for Mach numbers M>0.07 and for variation of particle number density delta(n)/n>0.1, but no steepening of the pulse was detected. The pulse propagation speed was found to be c...

Enhancement of cyclotron damping is theoretically evaluated based upon the wave E-field polarization which is modified by the two-ion hybrid resonance. The degree of enhancement and its asymmetry about the plasma center is consistent with experimental observations. The enhancement factor is very large at low plasma densities at which most of the past damping strength measurements have been repo...