The possibility of reconstruction of two-dimensional random inhomogeneities in a shallow sea by frequency shifts of the spatial interference structure of the sound field

Fluctuations of frequency shifts of the spatial interference structure of the sound field in the oceanic waveguide, caused by a two-dimensional field of a random perturbation, are described. Various schemes of observation point spacing are considered. The possibility is shown to reconstruct the spatial spectrum of waveguide perturbations by measuring the spatial spectrum of the frequency shift of the interference pattern. The results of the theoretical treatment are illustrated by the examples of background internal waves and bottom roughness. The sensitivity of monitoring based on measurements of frequency shifts of the interference structure of the sound field is estimated. For medium perturbations by background internal waves, the fluctuations of liquid layer vibrations, sound speed, and temperature, which are minimum detectable by frequency shifts of the interference pattern, were estimated.     

Method of acoustic sweep monitoring of oceanic inhomogeneities (Review)

Theoretical grounds of the new method of monitoring of the temporal variability of oceanic inhomogeneities, which uses the data on frequency shifts of interference maxima of the sound field, were described. The method is free of limitations on both the resolution of signals coming in individual modes (rays) and the adiabatic approximation underlying the conventional methods of inhomogeneity reconstruction. The monitoring sensitivity was estimated, which allows us to estimate minimum detectable changes in the speed of sound by measurement data on frequency shifts of local maxima. Experimental data on shifts of the frequency spectrum of a broadband low-frequency signal on a stationary path in a shallow sea were presented. On their basis, the possibility of applying this method to diagnose tidal variations was shown. Within a numerical simulation, model reconstruction of the frequency spectrum of background internal waves was considered on the basis of the data on measurements of the spectrum of frequency shifts of the interference maximum. The results of the spectrum reconstruction with and without focusing of the conjugate wave field are presented. The problems of monitoring stability and efficiency with respect to the interference pattern formed by various groups of modes were discussed.     

Theory of parametric excitation of acoustic waves

A theory of parametric excitation of acoustic waves is constructed. It is shown that nonlinear attenuation is the main restriction mechanism for a parametrically generated sound wave. The intensity of generated waves is directly proportional to the difference ε between the value of pumping and bare attenuation. The calculated proportionality coefficient depends on the shape of the generated sound wave. Why an ordinary pattern does not form for acoustic waves is explained. The structure of the spectrum of excited waves was studied. It is shown that this structure has exponential asymptotic behavior at the frequency. The width of the intensity distribution depends on the shape of a wave. For different cases it behaves as ε ^α with α=1, 8/7, and 4/3. The results are compared with the experimental data of Ref. 5. Zh. éksp. Teor. Fiz. 112, 1630–1648 (November 1997) Published in English in the original Russian journal. Reproduced here with stylistic changes by the Translation Editor.     

Frequency shifts of the sound field interference pattern in shallow water because of second-mode soliton-like internal waves

Numerical simulation is carried out to analyze the effect of an internal soliton of the second gravity mode on low-frequency sound propagation in an oceanic shelf region. The simulation is performed using the data of a full-scale experiment performed on the shelf of the South China Sea near Dongsha atoll, where the aforementioned solitons had been detected by stationary vertical thermistor arrays. The calculations take into account the effect of horizontal refraction of sound waves. It is assumed that a stationary acoustic track is oriented across the predominant propagation direction of internal waves. The results of simulation show that, when the soliton crosses the stationary track, some of the sound field modes are focused, whereas other modes are defocused. It is demonstrated that the soliton parameters can be adequately determined from the frequency shifts of the sound field interference pattern. However, such an estimate of the soliton parameters is only possible for a limited length of the stationary track for which the effect of horizontal refraction is sufficiently weak.     

Differential approximation for Kelvin wave turbulence

I present a nonlinear differential equation model (DAM) for the spectrum of Kelvin waves on a thin vortex filament. This model preserves the original scaling of the six-wave kinetic equation, its direct and inverse cascade solutions, as well as the thermodynamic equilibrium spectra. Further, I extend DAM to include the effect of sound radiation by Kelvin waves. I show that, because of the phonon radiation, the turbulence spectrum ends at a maximum frequency of ω* ∼ (ε³ c _s ²⁰ /κ¹⁶)^1/13, where ε is the total energy injection rate, c _s is the speed of sound, and κ is the quantum of circulation. The text was submitted by the author in English.     

Frequency shifts of sound field maxima in few-mode propagation, which are initiated by internal wave solitons

The problem of frequency shifts of sound field interference maxima, which are due to the motion of internal wave solitons in the ocean medium and cause intermodal transformation effects, has been solved for few-mode propagation regime. Simulation results are presented and the conditions of applicability of the adiabatic approximation, in which normal waves can be considered as independent, are discussed. The numerical experiment data are used to analyze the possibility of reconstructing the soliton parameters by measuring the frequency shifts of wave field maxima.     

Reconstruction of the spatial spectrum for an anisotropic field of background internal waves

A model reconstruction of the two-dimensional spatial spectrum is considered for an anisotropic field of background internal waves in shallow water. Solution of the inverse problem is based on the data on frequency shifts of the sound field interference maxima. Results of a numerical experiment are presented.     

Return current instability and its effects on beam-plasma system

The return current induced in a plasma by a relativisitc electron beam generates a new electron-ion two-stream instability (return current instability). Although the effect of these currents on the beam-plasma e-e instability is negligible, there exists a range of wave numbers which is unstable only to return current (RC) instability and not to e-e instability. The electromagnetic waves propagating along the direction of the external magnetic field, in which the plasma is immersed, are stabilized by these currents but the e.m. waves with frequencies,ω ²≪Ω _e ² ≪ω _pe ² (Ω _e andω _pe being cyclotron and plasma frequency for the electrons of the plasma respectively) propagating transverse to the magnetic field get destabilized. Heuristic estimates of plasma heating, due to RC instability and due to decay of ion-acoustic turbulence generated by the return current, are made. The fastest time scale on which the return current delivers energy to the plasma due to the scattering of ion-sound waves by the electrons can be ∼ω _pi ⁻¹ (ω _pi being the plasma frequency for the ions).     

Anomalies of internal friction in CsI single crystal at liquid helium temperatures caused by plastic deformation

Acoustic relaxation in undeformed and plastically deformed CsI single crystal has been studied using the composite oscillator technique at frequencies (1–7) × 10⁵ Hz in the temperature range 2–15 K. Plastic deformation leads to appearance of an internal friction peak localized in the temperature interval 4–5 K. It is shown that the peak shifts towards higher temperatures when increasing the vibration frequency and corresponds to a thermally activated relaxation process with very low values of the activation energyU ≈ 1.9×10⁻³ eV and the attack frequencyν ₀≈6.7 × 10³ s⁻¹. Interaction of sound with dislocation kinks migrating in the second order Peierls relief is considered as a possible mechanism of the peak. Research was made possible in part by Grants U9T000 and U9T200 from the International Science Foundation and supported in part by the Fundamental Research Foundation of Ukraine (Project 2.4/156 “Bion”).     

Reconstruction of spatial spectra of the isotropic field of background internal waves

Model reconstruction of the two-dimensional spatial spectra of isotropic background internal waves is considered in the framework of computer modeling. The solution of the inverse problem is based on information about the frequency shifts of interference maxima of an acoustic field. The results of reconstruction of spectra with and without focusing of the inverse wave field are presented. The possibilities of monitoring are illustrated in relation to the interference pattern formed by different modal composition.     

Frequency shifts of the spatial interference structure of the sound field in shallow water

A fluctuation model of the frequency shifts of the spatial interference structure formed by the sound field in a randomly inhomogeneous oceanic waveguide is constructed. The relation between the random fields of the perturbation-caused variation of the waveguide’s dispersion characteristic and the frequency deviation of a local interference maximum is analyzed. The applicability of the results to the cases of the waveguide perturbation by the background internal waves and by the roughness of the bottom relief is considered.     

Giant magnetoacoustic effect in KMnF3 due to nuclear spin waves

An explanation is proposed for the gigantic magnetoacoustic effect that we observed in KMnF₃ in previous work {Kh. G. Bogdanova, V. A. Golenishchev-Kutuzov, M. I. Kurkin et al., Zh. éksp. Teor. Fiz. 112, 1830 (1997) [JETP 85, 1001 (1997)]}. The effect entails a tenfold amplitude reduction of an acoustic pulse in a magnetic field that varies over the range 0–8 kOe. It is shown that this effect is due to the interference of two nuclear magnetoelastic waves propagating in the sample under magnetoacoustic resonance conditions, if this resonance occurs in the region of strong spatial dispersion of nuclear spin waves. The effect is said to be gigantic because it exceeds in magnitude the magnetoacoustic effects observed previously in magnetically ordered materials even though it is due to nuclear magnetism, which is 10⁵ times weaker than electronic magnetism. We observe a concomitant anomalous dependence of the dispersion of the velocity of sound on the external magnetic field. Zh. éksp. Teor. Fiz. 115, 1727–1739 (May 1999)     

Probability of the occurrence of freak waves

The statistics of the occurrence of freak waves on a surface of an ideal heavy liquid is studied. The freak (rogue, extreme) waves arise in the course of evolution of a statistically homogeneous random Gaussian wave field. The mean steepness of initial data varies from small (μ² = 1.54 × 10⁻³) to moderate (μ² = 3.08 × 10⁻³) values. The frequency of the occurrence of extreme waves decreases with an increase in the spectral width of the initial distribution, but remains relatively high even for broad spectra (Δ _k /Δ ∼ 1).     

The sensitivity of monitoring by measuring the frequency shifts of the sound field interference pattern

The sensitivity of the remote method of reconstructing the frequency spectrum of a water medium perturbation from the measured frequency shifts of the sound field interference peaks is investigated. On the basis of the Rayleigh criterion, an expression is derived for estimating the minimal frequency shift that allows the resolution of two neighboring peaks. The detection sensitivity for the sound velocity fluctuations caused by the time variability of the medium along the track is estimated. Results of computations for a perturbation in the form of background internal waves are presented.     

α + 8He Elastic Scattering with the Generator-Coordinate Method

 The elastic α + ⁸He phase shifts are calculated with a two-centre generator-coordinate method. The microscopic α and ⁸He internal wave functions are defined in the harmonic-oscillator model. Bound states and resonances of ¹²Be are obtained. Among them, a 4⁺ resonance with a molecular structure should be observable in elastic scattering. The parity dependence of the microscopic phase shifts is analyzed by fitting them with simple potentials. The odd-even effect is similar in the α + ⁸He and α + ⁶He phase shifts for low partial waves but decreases more rapidly with increasing orbital momentum for α + ⁸He. Received May 14, 1999; accepted for publication July 29, 1999     

Viscous compressible hydrodynamics at planes,spheres and cylinders with finite surface slip

We consider the linearized time-dependent Navier-Stokes equation including finite compressibility and viscosity. We first constitute the Green's function, from which we derive the flow profiles and response functions for a plane, a sphere and a cylinder for arbitrary surface slip length. For high driving frequency the flow pattern is dominated by the diffusion of vorticity and compression, for low frequency compression propagates in the form of sound waves which are exponentially damped at a screening length larger than the sound wave length. The crossover between the diffusive and propagative compression regimes occurs at the fluid's intrinsic frequency w \omega ∼ c ² r₀ \rho_{0}^{}/h \eta , with c the speed of sound, r₀ \rho_{0}^{} the fluid density and h \eta the viscosity. In the propagative regime the hydrodynamic response function of spheres and cylinders exhibits a high-frequency resonance when the particle size is of the order of the sound wave length. A distinct low-frequency resonance occurs at the boundary between the propagative and diffusive regimes. Those resonant features should be detectable experimentally by tracking the diffusion of particles, as well as by measuring the fluctuation spectrum or the response spectrum of trapped particles. Since the response function depends sensitively on the slip length, in principle the slip length can be deduced from an experimentally measured response function.     

Macroscopic and mesoscopic matter waves

It has been shown earlier [3,6] that matter waves which are known to lie typically in the range of a few angstrom, can also manifest in the macrodomain with a wave length of a few centimeters, for electrons propagating along a magnetic field. This followed from the predictions of a probability amplitude theory by the author [1,2] in the classical macrodomain of the dynamics of charged particles in a magnetic field. It is shown in this paper that this case constitutes only a special case of a generic situation whereby composite systems such as atoms and molecules in their highly excited internal states, can exhibit matter wave manifestation in macro and mesodomains, in one-dimensional scattering. The wave length of these waves is determined, not by the mass of the particle as in the case of the de Broglie wave, but by the frequency ω, of the classical orbital motion of the internal state in the correspondence limit, and is given by a nonquantal expression, λ = 2πv/ω, v being the velocity of the particle. For the electrons in a magnetic field the frequency corresponds to the gyrofrequency, Ω and the nonquantal wave length is given by λ = 2πv _|| /Ω; v _|| being the velocity of electrons along the magnetic field. Received 29 September 2001 / Received in final form 23 May 2002 Published online 19 July 2002     

Generation of coherent thermal phonons in amorphous dielectrics at room temperature induced by four-photon interaction

Resonant responses of Mandelshtam-Brillouin scattering from longitudinal and transverse acoustic waves at frequencies of ν _LS = ±1.15 cm⁻¹ and ν _TS = ±0.7 cm⁻¹, respectively, and at frequency of ν _SS = ν _TS $ \sqrt 3 $ \sqrt 3 = ±0.43 cm⁻¹ were detected in K8 optical glass at room temperature using four-photon spectroscopy. We attribute this effect to the induced generation of a second sound wave (coherent thermal phonons). The mechanisms of generation and the possibility of practical application of the observed effect for express diagnostics of the quality of transparent materials are discussed.     

Spontaneous interference bremsstrahlung effect in the scattering of a relativistic electron by a nucleus in the field of two light waves

This paper presents, for the general relativistic case, a theoretical study of nonresonance spontaneous bremsstrahlung by an electron scattered by a nucleus in the field of two elliptically polarized light waves propagating in the same direction. We show that there are two significantly different kinematic regions: the noninterference region where the main multiphoton parameters are the Bunkin-Fedorov quantum parameters γ _1,2, and the interference region where interference effects play an important role and where the quantum interference parameters α(±) act as multiphoton parameters. We encounter the spontaneous interference bremsstrahlung effect in two cases: in the special case of the same linear polarization of both waves, and in the general case of elliptical polarization of the waves. The effect manifests itself in the interference region and is due to stimulated, correlated emission and absorption of photons of both waves. For moderately strong fields, we find the cross sections of spontaneous bremsstrahlung by an electron scattered by a nucleus in the given kinematic regions. Finally, we show that the differential cross section in the interference region with correlated emission (absorption) of equal numbers of photons of both waves can be much greater than the corresponding cross section in any other geometry. Zh. éksp. Teor. Fiz. 116, 1210–1240 (October 1999)     

Effect of an electric field on the surface tension of a liquid at low temperatures

An external electric field changes the dispersion law of waves on the surface of a liquid. Besides the usual capillary term (∝k ³, k is the wave number) and gravitational term (∝k), a term quadratic in the wave vector appears in the expression for the square of the frequency in a homogeneous field. These excitations are associated with the variation of the coefficient of surface tension of the liquid at low temperatures. In the case of a large field tangent to the surface, the correction is proportional to T ^8/3, unlike the T ^7/3 correction in the absence of a field. Zh. éksp. Teor. Fiz. 111, 1369–1372 (April 1997)