Biomedical subjects

Vitalyi Gusev

Publications and source records attributed to Vitalyi Gusev.

14 recordsLinked to original sources

PubMed2006

Profiles of initially sinusoidal waves propagating in nonlinear microinhomogeneous materials.

The asymptotic analytical theory predicting acoustic wave profiles in microinhomogeneous materials with hysteretic quadratic nonlinearity and attenuation proportional to an even power of frequency is developed. The theory predicts that the influence on the nonlinear wave of the Rayleigh scattering of acoustic waves, which is proportional to the forth power of frequency, results in the net diminishing of wave attenuation. This is due to the suppression (diminishing) by scattering of the nonlinear hysteretic losses which is more important than direct increase in linear losses added by scattering.

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PubMed2005

Reflection and transmission at normal incidence onto air-saturated porous materials and direct measurements based on parametric demodulated ultrasonic waves.

The present work is related to the characterization of air-saturated porous media by using parametric demodulated ultrasonic waves. One uses two different powerful ultrasonic emitters working either at 47 kHz or at 162 kHz which are electronically amplitude modulated over the 200 Hz-4 kHz or 2 kHz-40 kHz bandwidths respectively. The demodulation process takes place in air, due to its nonlinearity enabling to generate audio range acoustical waves or alternatively low frequency ultrasonic waves which can be used to characterize porous materials in the reflection configuration at normal incidence. Some appropriate theoretical calculations are introduced for three configurations of interest, i.e. a porous slab, a porous layer mounted onto a rigid plate, and a porous half space, in the case of the equivalent-fluid model. Comparisons between theoretical modeling and experimental data are provided and prospective industrial applications are discussed.

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PubMed2005

Mathematical analysis of thermal diffusion shock waves.

Thermal diffusion, also known as the Ludwig-Soret effect, refers to the separation of mixtures in a temperature gradient. For a binary mixture the time dependence of the change in concentration of each species is governed by a nonlinear partial differential equation in space and time. Here, an exact solution of the Ludwig-Soret equation without mass diffusion for a sinusoidal temperature field is given. The solution shows that counterpropagating shock waves are produced which slow and eventually come to a halt. Expressions are found for the shock time for two limiting values of the starting density fraction. The effects of diffusion on the development of the concentration profile in time and space are found by numerical integration of the nonlinear differential equation.

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PubMed2005

Thermal diffusion shock waves.

The Ludwig-Soret effect or thermal diffusion, which refers to the separation of liquid mixtures in a temperature gradient, is governed by a nonlinear, partial differential equation in space and time. It is shown here that the solution to the nonlinear differential equation for a binary mixture predicts the existence of shock waves completely analogous to fluid shocks and obeys an expression for the shock velocity that is an exact analogue of the Rankine-Hugoniot relations. Direct measurements of the time dependent, spatial absorption profile of a suspension of nanometer sized particles subjected to a sinusoidal temperature field generated by a pair of continuous laser beams, as well as self-diffraction experiments, show motion of the particles in agreement with the predictions of nonlinear theory.

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PubMed2005

On the interaction of counterpropagating acoustic waves in resonant rods composed of materials with hysteretic quadratic nonlinearity.

An ordinary inhomogeneous integrodifferential equation for the profile of the acoustic wave in a resonant rod, composed of a material with hysteretic quadratic nonlinearity, is derived. It explicitly takes into account the interaction of the counterpropagating acoustic waves. It also incorporates the boundary conditions in the sense that all possible solutions of the equation satisfy the appropriate boundary conditions at the ends of the rod.

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PubMed2004

Transient unidirectional acoustic streaming in annular resonators.

Theoretical description of the transient process of the acoustic streaming excitation in a toroidal waveguide with driven walls is developed. Particular attention is paid to the analysis of the closed-loop (unidirectional) streaming excitation by purely propagating acoustic mode. This mode might be excited by proper phasing of the two localized acoustic sources. It is demonstrated that the evolution of the local streaming velocity can be non-monotonous in some points of the resonator cross-section. A numerical evaluation of the analytical solutions highlights the influence of the ratio of the acoustic boundary layer thickness to the waveguide width on the acoustic-streaming stabilization time. The results obtained for the acoustic streaming in the annular resonator can be useful for the analysis of the annular thermoacoustic engines and refrigerators. They might be also applied in microfluidics where there is a growing interest to different possible physical mechanisms of fluid pumping in microscale channels.

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PubMed2003

Self-induced hysteresis for nonlinear acoustic waves in cracked material.

A new phenomenon of self-induced hysteresis has been observed in the interaction of bulk acoustic waves with a cracked solid. It consists in a hysteretic behavior of material nonlinearity as a function of the incident pump wave amplitude. Hysteresis manifests itself in the self-action of the monochromatic pump wave and in the excitation of its superharmonics and of its subharmonics. The proposed theoretical models attribute the phenomenon to hysteresis in transition of the acoustically forced oscillation of cracks from a nonclapping regime to a regime of clapping contacts.

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PubMed2003

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. Nonlinear perturbation of the contacts by a stronger (pump) wave causes either softening or hardening of the sample, and induces either additional absorption or transparency for a weaker (probe) acoustic wave depending on frequency of the latter.

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PubMed2003

Acoustic streaming measurements in annular thermoacoustic engines.

Experiments with an annular thermoacoustic engine employing quasiadiabatic interaction between traveling acoustic waves and an inhomogeneously heated porous material indicate the presence of a closed-loop mass flux. A qualitative modeling of the enthalpy flux in the thermoacoustic core provides an opportunity to estimate the thermal convection associated with this mass flux, by using temperature measurement at different positions in the system. The estimated acoustically induced mass flux is in accordance with recent theoretical results.

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PubMed2002

Multiple focused-waves production by parametric mixing in a layer with hysteretic quadratic nonlinearity.

Nonlinear scattering of a weak probe wave by a strong pump wave in a layer with nonlinearity hysteresis is analysed. It is demonstrated that a spherical probe wave from a point source after nonlinear process of difference frequency excitation is scattered in several foci. Different foci correspond to different frequencies of the transformed wave spectrum. In the case of a plane pump wave and under the condition that nonlinear scattering proceeds without acoustic mode conversion wave front reversal is possible. To achieve wave front reversal in a layer with hysteretic quadratic nonlinearity the pump wave should have a frequency equal to the frequency of the probe wave or to any of its subharmonics.

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PubMed2002

Theory of non-collinear interactions of acoustic waves in an isotropic material with hysteretic quadratic nonlinearity.

A particular form of the energy potential (cubic in strains) is proposed, which leads to the bow-tie behavior of the nonlinear modulus in an isotropic material with hysteresis of quadratic nonlinearity. The nonlinear scattering of a weak probe wave in the field of a strong pump wave is analyzed. It is demonstrated that collinear interactions of the shear waves are allowed in materials with nonlinearity hysteresis. Both in collinear and non-collinear frequency-mixing processes the combination frequency is composed of the probe wave frequency and one of the even harmonics of the pump wave. In general, the developed theory predicts that in the presence of the hysteretic nonlinearity the number of possible resonant scattering processes increases. In particular, if frequency-mixing processes are forbidden in the material with the elastic quadratic nonlinearity (for a fixed ratio of primary frequencies), they may be allowed in the materials with hysteretic quadratic nonlinearity. Moreover, in materials with hysteresis of the nonlinearity the resonant frequency mixing for a fixed ratio of primary frequencies may be allowed for multiple mutual orientations of the primary wave vectors.

Acoustics↗

PubMed2002

Nonlinearity of acoustic waves at solid-liquid interfaces.

The small-amplitude and finite-amplitude propagation characteristics of laser line source excited and laser detected Scholte waves are investigated. Acoustic waves with Mach numbers up to 0.054 are observed at the interface between water and glass. In our case of a hard solid-liquid interface, the Scholte wave propagates very much like a bulk wave, for which the simple-wave equation holds. The experimental results are well fitted with this model, extended with an attenuation term. An anomalously large (compared with low amplitude viscous effects) attenuation reveals possible leakage of energy from the Scholte wave to bulk waves, through a mechanism of nonlinear mixing between the different wave modes and viscosity induced turbulence.

Acoustics↗

PubMed2002

Acoustic streaming related to minor loss phenomenon in differentially heated elements of thermoacoustic devices.

It is demonstrated that the differentially heated stack, the heart of all thermoacoustic devices, provides a source of streaming additional to those associated with Reynolds stresses in quasi-unidirectional gas flow. This source of streaming is related to temperature-induced asymmetry in the generation of vortices and turbulence near the stack ends. The asymmetry of the hydrodynamic effects in an otherwise geometrically symmetric stack is due to the temperature difference between stack ends. The proposed mechanism of streaming excitation in annular thermoacoustic devices operates even in the absence of thermo-viscous interaction of sound waves with resonator walls.

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PubMed2002

Strain wave evolution equation for nonlinear propagation in materials with mesoscopic mechanical elements.

Nonlinear wave propagation in materials, where distribution function of mesoscopic mechanical elements has very different scales of variation along and normally to diagonal of Preisach-Mayergoyz space, is analyzed. An evolution equation for strain wave, which takes into account localization of element distribution near the diagonal and its slow variation along the diagonal, is proposed. The evolution equation provides opportunity to model propagation of elastic waves with strain amplitudes comparable to and even higher than characteristic scale of element localization near Preisach-Mayergoyz space diagonal. Analytical solutions of evolution equation predict nonmonotonous dependence of wave absorption on its amplitude in a particular regime. The regime of self-induced absorption for small-amplitude nonlinear waves is followed by the regime of self-induced transparency for high-amplitude waves. The developed theory might be useful in seismology, in high-pressure nonlinear acoustics, and in nonlinear acoustic diagnostics of damaged and fatigued materials.

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