Stochastic generation accompanying parametric excitation of spin waves in yttrium iron garnet films

We report the results of experimental investigations of chaotic self-modulation of the envelope of surface spin waves as a result of first-order spin-wave parametric instability. The experimental apparatus consisted of a microwave oscillator with a spin-wave delay line in the feedback circuit. Pis’ma Zh. Tekh. Fiz. 24, 66–72 (April 12, 1998)     

Generation of dissipative structures in self-oscillating ring systems upon parametric interaction of spin waves

A quasi-periodic sequence of pulses in a self-oscillating ring system with a resonant amplifier and a ferromagnetic film has been generated upon three-wave parametric interaction of spin waves. It is established that the generated pulses are analogs of dissipative bright solitons, which are formed as a result of competition between amplification and loss, as well as between time dispersion and nonlinearity. To describe the mechanism of formation of these structures, we have proposed a model in the form of three parametrically coupled differential equations with amplification and a differential equation of linear oscillator. Under certain assumptions, this model has analytical solutions in time in the form of structures with a profile similar to that of bright solitons.     

High-energy proton generation under surface discharge conditions

A combined nanosecond pulsed electric discharge, whereby the breakdown proceeds simultaneously over a dielectric surface and across the interelectrode gap, has been studied. A beam of accelerated protons is generated in this system with a maximum energy of up to 350 keV that exceeds the high-voltage source potential. The phenomenon of selective acceleration of hydrogen ions has been observed. It is established that the probability of ion generation depends on the electrode polarity.     

Gasdynamic perturbations under conditions of surface microwave discharge in air

An investigation is performed of gasdynamic perturbations arising in the neighborhood of a dielectric antenna, on the external surface of which a microwave discharge is initiated at high pressures of air, where the electron-molecule collision frequency is much higher than the circular frequency of electromagnetic field. The time dependence of gas temperature is obtained for different values of power input, and it is demonstrated that, in the stage of formation of discharge at atmospheric pressure of air, the gas is heated at a rate of 30–70 K/μs. The electron concentration in plasma channels at atmospheric pressure does not exceed 10¹⁵–10¹⁶ cm⁻³. A study is made of the evolution of shock waves arising under conditions of surface micro-wave discharge at different pressures of surrounding gas, different durations of stimulation, and different power inputs to the discharge. It is demonstrated that the shock wave velocity in the vicinity of the antenna reaches a value of 1 km/s.     

Parametric generation of acoustic waves and mode-locking of spin waves through magnetoelastic coupling

A YIG disk with parallel and polished surfaces was bonded onto a quartz rod with a transducer attached to it. The YIG sample was placed in a microwave cavity in a parallel-pumping configuration. For microwave power several decibels above the threshold for spin-wave instability, parametric generation of low-frequency acoustic waves was observed, and was accompanied by the simultaneous appearance of low-frequency modulation of the microwave reflected power. The effects were attributed to the beating of spin-wave side bands with the central band. The existence of side bands was confirmed by measuring the spin-wave spectrum. In the mode-locking experiment, a low-frequency acoustic wave was sent into the YIG sample through the transducer. Experimental evidences show that the acoustic wave, through magnetoelastic coupling, not only locks the phase but also enhances the amplitude of the sidebands relative to the central band.     

Effect of thermocapillarity on parametric excitation of surface waves

It is demonstrated that the thermocapillarity effect can either raise or lower the threshold of surface wave excitation, depending on the conditions of heating.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 46, No. 3, pp. 424–428, March, 1984.     

Criteria for the existence of generalized surface spin waves

A criterion for the existence of generalized surface spin waves is proposed on the basis of an analysis of the dipole-exchange surface spin dynamics of a tangentially magnetized, semibounded, easy-axis antiferromagnet. Pis’ma Zh. Tekh. Fiz. 24, 70–75 (July 12, 1998)     

Phase locking and rotational motion of a parametric pendulum in noisy and chaotic conditions

The effect of noise on the rotational mode of a pendulum which is excited kinematically in vertical direction has been analysed. We have shown that for weak noise, transitions from the oscillations to rotations and vice versa are possible. For stronger noise, the rotational solution as an independent synchronized mode vanishes. When searching for the rotational motion we observed an intermittent transition to chaos induced by noise.     

Phase conjugation in four-wave mixing of cw radiation under conditions of strong self-interaction

An experimental investigation is made of the influence of strong self-interaction of the reference waves on phase conjugation in four-wave mixing of cw radiation in a medium with a thermal nonlinearity. It is shown that the thermal lens formed by the Gaussian reference beams reduces the nonlinear reflection coefficient appreciably (several-fold) and causes a deterioration in the phase conjugation quality. Pis’ma Zh. Tekh. Fiz. 23, 60–63 (August 12, 1997)     

Remote laser generation of narrow-band surface waves through optical fibers

This paper demonstrates the use of a fiberoptic bundle for flexible, compact, remote, and noncontact laser generation of surface ultrasonic waves in materials. The bundle is able to deliver Nd:YAG pulsed light with a 60% delivery efficiency up to an average energy of 55 mJ/pulse for a pulse duration on the order of 10 ns and a pulse repetition rate of 20 Hz without signs of fiber damage. Details of the bundle construction and surface preparation are given, and pulsed light delivery tests performed with single tapered fibers are discussed. The high-power light delivery capabilities of the bundle are demonstrated for the generation of narrow-band surface waves in a Carbon/PEEK composite laminate by a spatial modulation technique that employs a periodic transmission mask. Single laser pulse ultrasonic tonebursts are clearly detectable using a small aperture piezoelectric transducer while ensuring thermoelastic generation conditions. The theory of narrow-band generation of surface acoustic waves is improved by accounting for the strength nonuniformity of the illumination sources. In addition, the effect of the number of illumination sources on the bandwidth of the generated surface wave is assessed experimentally, and excellent agreement is shown with the theoretical results predicted by the improved model.     

Experimental study of the parametric interaction between space-charge waves in thin-film GaAs-based semiconductor structures

An experiment on the effect of low-frequency pumping on the output spectrum of a thin-film n-GaAs semiconductor structure with electron drift is reported in the 3-cm and 8-mm wavelength intervals. It is found that the presence of a low-frequency pump signal, whose power greatly exceeds that of a test signal, considerably enhances microwave transfer within two frequency bands separated by Δf=f _s−f _p, where f _s is the frequency of a weak test signal and f _p is the frequency of the pump signal (f _p<f _s). The transfer enhancement is evidence of the existence of effective parametric coupling between space-charge waves in the drift electron stream. This effect confirms the conclusions of previous theoretic studies.     

Acoustoionic interaction of SH surface waves with dilute ionic solutions

A theory describing the acoustoionic interaction of shear horizontal (SH) surface waves with viscous conductive ionic liquid is presented. A Green's function formulation that accounts for the acoustoelectric interaction with ions and dipoles in the solution is obtained for the surface potential in terms of the liquid and piezoelectric crystal parameters. For dilute ionic solutions, simple closed-form expressions for the velocity change and attenuation are obtained in terms of liquid conductivity and dielectric constant and the piezoelectric coupling coefficient. It is shown that SH surface waves in particular and acoustic waves in general can be used to perform microanalysis of dilute ionic solutions, detecting conductivity, dielectric constant, and relaxation frequency. The analysis, which was done for a simple crystal class, the hexagonal (6 mm), shows results which compare very well with exact numerical computations.     

Effect of heating on parametric excitation of waves on the surface of a liquid

The threshold of excitation and the wave numbers of parametric waves on the surface of a layer of viscous incompressible liquid undergoing harmonic vibrations along a vertical axis are determined for an equilibrium temperature gradient.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 32, No. 4, pp. 708–711, April, 1977.     

参外联合激励下一类混沌系统的动力学机理

旨在揭示频域两尺度耦合导致的快慢效应及其产生的机理.以一类典型的混沌系统为例,引入参外联合激励,当两激励频率远小于系统固有频率时,会产生诸如簇发振荡等特殊行为.考虑了两激励频率满足严格共振和非严格共振两种情形下系统的动力学特性.基于两种情形下的广义自治系统随慢变量变化的分岔分析,得到了两种情形下不同的簇发振荡及其分岔机...     

The influence of vacuum conditions on the microwave generation in a vircator

The effect of residual gases on the lifetime of a virtual cathode (VC) was studied. Dependence of the output pulse energy of a high-power vircator on the vacuum conditions was studied. It is demonstrated that a rough vacuum of 5×10^?4 Torr achieved with a mechanical pump is sufficient for a vircator operation without significant loss of the output radiation energy. The experimental data agree with a model of the mechanism of VC degradation as a result of the gas ionization.     

多功能球形螯合吸附剂的微波辐射制备研究

以腈纶废丝为原料,二甲基甲酰胺和分散剂溶液分别为溶剂和非溶剂,通过相转换法制得聚丙烯腈珠体,再采用微波辐射法对珠体进行改性,制得一种多功能球形螯合吸附剂SPDA,并对SPDA进行理化性能表征。研究表明,SPDA含有酰胺基和咪唑基等多种特征官能团,改性的最佳条件为单体和珠体质量比为7∶1,催化剂质量占珠体质量14.0%,乙二醇和珠体质量比为7∶5,微波功率为640W,辐射反应5min。采用静态吸附法研究SPDA对Cr(Ⅵ)的吸附效果,当pH值为4,Cr(Ⅵ)的初始质量浓度为120mg/L,吸附时间为2h,吸附温度为30℃时,去除率达到96.2%,平衡吸附容量可达38.5mg/g。     

The effect of surface waves on the interaction of incident particles with a solid surface

The incidence of two particles onto a thin solid plate has been studied by means of computer simulation. The influence of the impact-excited waves on the particle-surface interaction is considered. The waves excited in the target plate produce a significant change in the surface response dynamics. The distribution of surface damage and plastic strain generated by the incident particles is analyzed, and it is established that this distribution is correlated with the surface wave structure.     

Small-size ultralow-voltage generator of chaotic microwave oscillations

The scheme of a small-size ultralow-voltage generator of broadband chaotic microwave oscillations is considered. Results of numerical modeling and experimental investigation of the device prototype operating in various regimes are summarized. Good prospects of the proposed ultralow-voltage generator (vircator) are related to the relatively low accelerating voltages (below 1000 V), rather high electron beam currents (up to 800 mA), good efficiency (up to 5%), and small dimensions of the device.     

Generation of chaotic microwave pulses with the help of passive synchronization of spin wave self-modulation frequencies in self-oscillatory ring systems

Passive synchronization (PS) of spin wave self-modulation frequencies of a chaotic microwave signal has been observed for the first time in a self-oscillatory ring system involving a nonlinear passive element with saturable absorption. The development of PS led to the generation of a periodic train of chaotic microwave pulses with an off/duty ratio exceeding 20. It is established that the repetition period of chaotic microwave pulses can be controlled by changing gain in the ring system.