Anomalies in the ultrasound reflection from a solid-dissipative medium interface

The reflection of longitudinal acoustic waves from the interface between a solid and a strongly dissipative medium was theoretically studied. It is shown that the reflection coefficient and the reflected signal phase significantly depend on the coefficient of ultrasound absorption in the dissipative medium. An algorithm for restoring the time variation of the dissipative medium viscosity during solidification is proposed, which is based on the results of measurements of the amplitude reflection coefficient for a pulsed ultrasonic signal. The reflection and transmission coefficients are determined for the ultrasound wave amplitude, velocity, pressure, and intensity. An expression is derived for the acoustic energy absorbed upon reflection from a dissipative medium. A frequency dependence of the amplitude and generalized phase of the signals reflected from and transmitted through the interface are restored from the results of spectral calculations. The theoretical results are confirmed by experimental data on the reflection of acoustic pulses from an organic glass-epoxy compound resin interface measured during solidification of the latter medium. According to these data, the reflection coefficient and the reflected acoustic pulse duration decreased upon solidification of the epoxy compound.     

Plasma wave reflection from a boundary with specular accommodative boundary conditions

In the present work, linearized problem of plasma wave reflection from a boundary of a half-space is solved. Specular accommodative conditions of plasma wave reflection from the boundary are taken into consideration. Wave reflectance is found as function of the given parameters of the problem, and its dependence on the normal electron momentum accommodation coefficient is shown. Longwave limit of the solution is analyzed.     

Acoustic reflection from the boundary of anisotropic thermoviscoelastic solid with fluid

Vertical slownesses of waves at a boundary of an anisotropic thermoviscoelastic medium are calculated as roots of a polynomial equation of degree eight. Out of the corresponding eight waves, the four, which travel towards the boundary are identified as upgoing waves. Remaining four waves travel away from the boundary and are termed as downgoing waves. Reflection and refraction of plane harmonic acoustic waves are studied at a plane boundary between anisotropic thermoviscoelastic solid and a non-viscous fluid. At this fluid-solid interface, an incident acoustic wave through the fluid reflects back as an attenuated acoustic wave and refracts as four attenuating waves into the anisotropic base. Slowness vectors of all the waves in two media differ only in vertical components. Complex values of vertical slowness define inhomogeneous refracted waves with a fixed direction of attenuation, i.e. perpendicular to the interface. Energy partition is calculated at the interface to find energy shares of reflected and refracted waves. A part of incident energy dissipates due to interaction among the attenuated refracted waves. Numerical examples are considered to study the variations in energy shares with the direction of incident wave. For each incidence, the conservation of incident energy is verified in the presence of interaction energy. Energy partition at the interface seems to be changing very slightly with the azimuthal variations of the incident direction. Effects of anisotropy, elastic relaxation and thermal parameters on the variations in energy partition are discussed. The acoustic wave reflected from isothermal interface is much significant for incidence around some critical directions, which are analogous to the critical angles in a non-dissipative medium. The changes in thermal relaxation times and uniform temperature of the thermoviscoelastic medium do not show any significant effect on the reflected energy.     

Anomalies of the specific heat in the vicinity of the phase transition from isotropic liquid to nematic liquid crystal

Precision measurements were made of the specific heat in the vicinity of the phase transition from nematic liquid crystal to isotropic liquid, an analysis of the results indicating that this transition occurs near the tricritical point.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 39, No. 6, pp. 1110–1107, December, 1980.     

Effects of electrochemical processes on the reflection of ultrasonic pulses from an electrolyte-metal boundary

Conclusion Experiments have been performed on the ultrasonic reflection coefficients for metal electrodes in electrolytes in relation to the current and electrode material. In particular, there is a large increase in the reflection coefficient in the initial period of current flow.Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 27, No. 4, pp. 124–125, July–August, 1991.     

Elastic reflection of4He atoms from the surface of liquid4He

The reflection of incident⁴He atoms from the surface of liquid⁴He can yield information on the microscopic features of the liquid at the surface. Edwards et al. have measured this reflectivity and have developed a theoretical model which successfully described the measurements. However, the density profile of the liquid⁴He surface has recently been determined experimentally, and this can now be used to model the reflectivity without any freely adjustable parameters. We use this density profile and the experimentally-determined interatomic pair potential to derive an effective potential for the incoming atom, and then solve the single-particle Schroedinger equation to find the reflectivity as a function of wavevector perpendicular to the surface. Within the uncertainty in the density profile and interatomic potential, we have chosen values that give good agreement between the measured and calculated reflectivities.     

4He atom reflection from rough liquid4He surfaces

When an atom is evaporated from or added to a free liquid surface there is a density perturbation of the surface. We have detected this surface spoiling using a⁴He atomic beam at glancing angles to the surface. With a perfect free liquid surface some of the atoms reflect specularly and some condense. We find that the specular reflection coefficient decreases as the surface is spoiled by another beam of⁴He atoms. The degree of spoiling as measured by the decrease in reflectivity, is initially proportional to the spoiling beam flux, but at higher fluxes the spoiling saturates. A phenomenological model is developed to describe this behaviour.     

Effect of waves at the interfacial boundary on the desorption of a gas from the bulk of a liquid

An experimental investigation has been made of the effects of artificially excited two-dimensional gravity waves on the process of interfacial mass transfer during desorption of CO₂ from a layer of liquid of uniform depth. A simple dimensionless relationship is proposed for calculating mass transfer coefficients during the use of such means for intensifying processes.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 53, No. 5, pp. 790–795, November, 1987.     

Release of hydrogen from an insulating liquid under the action of ultrasound

Coherent anti-Stokes light scattering spectroscopy is used to study the release of hydrogen from an insulating liquid under the action of focused ultrasound which causes mixing of the liquid to form a fountain. It is shown that the action of ultrasound on an insulating liquid in an evacuated volume or in normal-pressure air substantially accelerates the desorption of hydrogen into the gas phase. Pis’ma Zh. Tekh. Fiz. 24, 79–84 (January 12, 1998)     

Time-resolved total internal reflection fluorometry study on polarity at a liquid/liquid interface

The polarity of a water/oil (oil: cyclohexane, carbon tetrachloride, toluene, chlorobenzene, o-dichlorobenzene, or 1,2-dichloroethane) interface was investigated by means of time-resolved total-internal-reflection (TIR) fluorescence spectroscopy of a polarity-sensitive probe: sulforhodamine B (SRB). In bulk solutions, the nonradiative decay rate constant of SRB increased with an increase in a solvent polarity parameter [ET(30)], and this relationship was used to estimate the polarities of water/oil interfaces. For the oil having a relatively low solvent polarity [ET(30) < 35 kcal/mol], the polarity of the water/ oil interface agreed with that of the arithmetic average of the polarities of the two phases [ET(30)calc]. For water/odichlorobenzene and water/1,2-dichloroethane interfaces [ET(30) of the oil > 35 kcal/mol], on the other hand, the interfacial polarity determined by TIR spectroscopy was lower than the ET(30)calc. The results are discussed in terms of thickness/roughness of the water/oil interface.     

Slip effects on the peristaltic flow of a non-Newtonian Maxwellian fluid

Summary In real systems there is always a certain amount of slip, which, however, is hard to detect experimentally because of the required space resolution. In this paper, we analyze the effect of slip boundary conditions on the dynamics of fluids in porous media by studying the flow of a Newtonian and non-Newtonian Maxwellian fluid in an axisymmetric cylindrical tube (pore), in which the flow is induced by traveling transversal waves on the tube wall. Like in peristaltic pumping, the traveling transversal waves induce a net flow of the liquid inside the pore. The viscosity as well as the compressibility of the liquid is taken into account. This problem has numerous applications in various branches of science, including stimulation of fluid flow in porous media under the effect of elastic waves and studies of blood flow dynamics in living creatures. The Navier-Stokes equations for an axisymmetric cylindrical pore are solved by means of a perturbation analysis, in which the ratio of the wave amplitude to the radius of the pore is small parameter. In the second order approximation, a net flow induced by the traveling wave is calculated for various values of the compressibility of the liquid, relaxation time and Knudsen number. The calculations disclose that the compressibility of the liquid, Knudsen number of slip flow and non-Newtonian effects in presence of peristaltic transport have a strong influence of the net flow rate. The effects of all parameters of the problem are numerically discussed and graphically explained.     

Ultrasonic reflection from a stressed interface

In seeking to develop an NDE technique for verifying the serviceability of NiTi couplers for plumbing unions, it was found that the reflection coefficient for a normally incident ultrasonic wave correlated with the stress level at the NiTi-tubing interface. Current theory pertaining to interface reflection is not complete but, even at present status, there is semiquantitative accord between theoretical predictions and normalized data for reflection coefficient versus stress level. These results are at fixed frequency and with comparable surface roughness. Variation of either frequency or surface roughness further affects the reflection coefficient. Current studies are being pursued to define this effect.     

Modeling the instability of the boundary of a dielectric liquid with a free surface charge

We have numerically modeled the development of instability of the boundary of a nonviscous dielectric liquid with a free surface charge occurring in an external electric field and compared the behavior of this system in the two limiting cases, whereby the surface charge produces complete screening of the field above and below the surface. Although the linearized equations of motion in the two cases coincide, the scenarios of instability development are substantially different, which is indicative of the determining role of nonlinearity in this process.     

Action of ultrasound on the rise of a liquid in a capillary tube and its dependence on the properties of the liquid

The dependence of the ultrasonic capillary effect on the viscosity, vapor pressure, surface tension, and gas content of the liquid is investigated.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 39, No. 3, pp. 513–519, September, 1980.     

Optical reflection from a semiinfinite nonlinear crystal

Multistability of the reflection coefficient as a function of incident amplitude is theoretically demonstrated to be possible for a semiinfinite optically homogeneous medium with the Kerr nonlinearity. The multistability arises at certain relations between the system parameters. The treatment is essentially free from the assumption that field envelopes vary slowly in space. Underlying physical processes are described.     

Anomalies of the Boundary Reflection of Ultrasound from the Film of a Dissipative Medium

Theoretical consideration has been given to the reflection of continuous and pulsed longitudinal and transverse acoustic waves from the film of a dissipative medium which is in contact with a solid-state half-space. It has been shown that the reflection coefficient and its phase substantially depend on the coefficient of attenuation of ultrasound in the dissipative-medium film and on its phase thickness. The shape of the reflected acoustic pulsed signal has been calculated using software. The application of the results obtained to investigation of the acoustic properties of viscous fluids is discussed.     

Stability of the boundary layer of liquid under a nonuniform temperature distribution of the surface

We study the effect of a longitudinal gradient of the surface temperature on the stability of the boundary layer of an incompressible liquid. A comparison shows a good agreement of the results with experimental data.     

Kinetics of heat transfer to a spherical particle from a rarefied plasma. 3. Maxwellian ion approximation

A. A. Baikov Metallurgical Institute, Russian Academy of Sciences, Moscow. Translated from Inzhenerno-fizicheskii Zhurnal, Vol. 62, No. 2, pp. 254–260, February, 1992.