Acoustical Physics最新文献

Variations of physical properties of seawater (sound speed, temperature, salinity, and density) over the southern shelf of the Caspian Sea were assessed. Furthermore, the effect of monthly changes in physical structure and layering procedure was evaluated on water characteristics. The influence of the thermal structure and stability of the water column in warm months on the sound speed was greater than that of the salinity parameter. Due to the high correlation between sound speed and temperature in the Caspian Sea water, their vertical structures are mostly correlated. The range of surface layer water changes was within 9–30°C during different months of the year. The water salinity in the areas away from the coast was measured around 12 to 12.5 PSU. The range of measured sound speed data in February was about 1450–1463 m/s, while the values recorded in June‑July were between 1501–1451 m/s. The results indicated formation of a deep acoustic channel in the middle and deep areas of the seawater column. The analysis revealed that the axis of the sound channel occurs at a depth of 140–150 m (intermediate layer) in warm months. The axis of the sound channel was located in upper layers in the warm months.

The temperature dependences of the heat capacity were measured and the general patterns of the formation of the phonon spectrum of single crystals of solid solutions of yttrium-lutetium aluminum garnets Y_{3 – x}Lu_xAl₅O₁₂ at 0 ≤ x ≤ 3 were investigated in the temperature range from 1.9 to 220 K. According to the data obtained at temperatures below 10 K, the Debye temperatures were calculated. The features of the phonon spectrum in the intermediate temperature range are interpreted as a superposition of optical modes for yttrium and lutetium garnets. It is shown that the low heat capacity values due to the contribution of acoustic phonons for Y_2.25Lu_0.75Al₅O₁₂ correlate with anomalies in the concentration dependences of the phonon transport, the absorption of acoustic waves, and the shape of the aluminum NMR line.

The article focuses on studying the effect of variable thermal conductivity on the reflection of waves propagating through a medium. Considered solid is half space with semiconductor properties. Additionally, we have also introduced the concept of non-local thermoelasticity to develop a stress-strain relation. Using the Helmholtz decomposition principal, we have determined that three longitudinal waves and one transverse wave propagate through the medium after reflection. To account for the thermal signals generated by the elastic vibration, we have used a three-phase lag (3PL) heat conduction model. The numerical computation of the theoretical results is presented graphically for a specific medium. The study of elastic waves passing through the human body is used for diagnosis and treatment. Nature and characteristics of the materials can also be detected by evaluating the behavior of waves reflected and transmitted through them.

Symmetric Lamb waves with a phase velocity exceeding the expansion wave velocity in an infinite medium are considered. It has been proven that internal waves (i.e., solutions of the wave equation, which have zero values of the strain and stress components on the surface and nonzero values in the plate bulk) may exist in this region of phase velocities. Parameters of the internal waves (phase velocity, frequency, and wavelength) are calculated; it has been proven that frequencies of the internal waves with the same phase velocity make an arithmetic progression. Several internal waves are considered, and cross sections of the corresponding strained plates are presented (as well as the distributions of the maximum tension and shear values).

The paper reports some results of experimental study on the effect of 3D-printing on the linear and nonlinear elastic properties of ABS polymer specimens manufactured in the form of thin filaments with 100% filling. The initial and 3D-printed ABD polymer specimens were studied by the static and Thurston–Bragger methods. Linear and nonlinear Young’s moduli and second-order nonlinear acoustic parameters were determined for several loading–unloading cycles of a specimen. It has been shown that the selected 3D-printing mode does not almost change the strength characteristics of ABS polymer, and its plastic characteristics even become slightly better. It has been revealed that mechanical loading has different effects on the nonlinear parameter of the initial and 3D-printed specimens. For the 3D-printed specimen, the nonlinear parameter is observed to decrease with increasing load.

An experimental verification of the possibility of estimating the coordinates of a mobile marine robot using spatially offset small-sized vector–scalar arrays, a broadband source placed on board the robot, and a remote polyharmonic permanently installed source—a beacon, which is used to eliminate bearing shifts caused by rotating receiving arrays under the action of underwater currents. It is shown that the use of technical means installed in the waveguide makes it possible to solve the triangulation problem and determine the horizontal coordinates of the robot, while taking into account the ray structure provides a depth estimate.

Acoustic attenuation coefficient per unit frequency square has been calculated for pure semiconductors like silicon and germanium, as well as for mixed semiconductors like gallium arsenide (III–V group) and tin telluride (IV–VI group), for longitudinal waves travelling along the (leftlangle {100} rightrangle ) crystallographic axis, within the temperature range 80–300 K. Second-order elastic constants of the materials are used to calculate the average Gruneisen parameter (leftlangle {{{gamma }}_{i}^{j}} rightrangle ), using which the nonlinearity parameter D_L has been calculated for different temperatures. The knowledge of D_L is used for calculation of acoustic attenuation coefficient per unit frequency square due to phonon–phonon interaction ({{left[ {{{{alpha }} mathord{left/ {vphantom {{{alpha }} {{{f}^{2}}}}} right. kern-0em} {{{f}^{2}}}}} right]}_{{text{L}}}}) and thermoelastic losses ({{left[ {{{{alpha }} mathord{left/ {vphantom {{{alpha }} {{{f}^{2}}}}} right. kern-0em} {{{f}^{2}}}}} right]}_{{{text{th}}}}}). Acoustic attenuations are found to be temperature dependent and increases with it. The magnitude of acoustic attenuation per unit frequency square due to phonon–phonon interactions is greater than that due to thermoelastic losses. The magnitude of acoustic attenuation for the investigated semiconductors is in the order Si < Ge < GaAs < SnTe. It is observed that anharmonicity of the solids which give rise to phonon–phonon interaction is the dominant cause of acoustic attenuation of propagating waves. The acoustic attenuation of propagating waves is found to be proportional to the molecular weights of semiconductors.