Thermoelastic mechanism for logarithmic slow dynamics and memory in elastic wave interactions with individual cracks.

Logarithmic-in-time slow dynamics has been found for individual cracks in a solid. Furthermore, this phenomenon is observed during both the crack acoustic conditioning and the subsequent relaxation. A thermoelastic mechanism is suggested which relates the log-time behavior to the essentially 2D character of the heating and cooling of the crack perimeter and inner contacts.

Observation of chaotic dynamics in a powerful backward-wave oscillator.

Self-modulation regimes of generation in a powerful 10-micros X-band backward-wave oscillator were studied theoretically and experimentally. The sequence of the self-modulation patterns and corresponding bifurcation values observed as the current was increased were in good agreement with the results of simulations. It was found that at a current of 120 A chaotic self-modulation set in at a power of 2 MW and a relative spectral width of 4%.

Luxemburg-gorky effect retooled for elastic waves: a mechanism and experimental evidence.

A new mechanism is proposed for the linear and amplitude-dependent dissipation due to elastic-wave-crack interaction. We have observed one of its strong manifestations in a direct elastic-wave analog of the Luxemburg-Gorky effect consisting of the cross modulation of radio waves at the dissipative nonlinearity of the ionosphere plasma. The counterpart acoustic mechanism implies, first, a drastic enhancement of the thermoelastic coupling at high-compliance microdefects, and, second, the high stress-sensitivity of the defects leads to a strong stress dependence of the resultant dissipation.

Observation of the "Luxemburg-Gorky effect" for elastic waves.

An experimental observation of a new nonlinear-modulation effect for longitudinal elastic waves is reported. The phenomenon is a direct elastic wave analogy with the so-called Luxemburg-Gorky (L-G) effect known over 60 years for radio waves propagating in the ionosphere. The effect consists of the appearance of modulation of a weaker initially non-modulated wave propagating in a nonlinear medium in the presence of an amplitude-modulated stronger wave that produces perturbations in the medium properties on the scale of its modulation frequency.

High-efficiency single-mode free-electron maser oscillator based on a bragg resonator with step of phase of corrugation.

A new type of high-selective Bragg resonator having a step of corrugation inside the interaction region was used as a microwave system for a free-electron maser (FEM). Using a LINAC LIU-3000 (1 MeV/200 A/200 ns) to drive the FEM oscillator, a single-mode single-frequency operation was achieved at a frequency of 30.74 GHz with an output power of about 50 MW, which corresponded to a record efficiency of 35% for a millimeter wavelength FEM.