Khalatnikov I.M., Kamenshchik A.Yu., Starobinsky A.A. «Quasi-isotropic expansion for a two-fluid cosmological model containing radiation and string gas» Журнал экспериментальной и теоретической физики, 156, № 4, с. 581-584 (2019)

Extended Abstract. The full text of this paper is published in the English version of JETP.

Khalatnikov I.M., Kamenshchik A.Yu., Starobinsky A.A. «Quasi-isotropic expansion for a two-fluid cosmological model containing radiation and string gas» Журнал экспериментальной и теоретической физики, 156, № 4, с. 581-584 (2019)

Extended Abstract. The full text of this paper is published in the English version of JETP.

Kirsanov M.N. «Lower estimate of the fundamental frequency of natural oscillations of a truss with an arbitrary number of panels» Вестник Московского государственного строительного университета, 14, № 7, с. 844-851 (2019)

The paper deals with oscillations of a statically definable plane, truss with a double lattice of racks and descending braces with massive loads in the nodes of the lower chord. The weight of the truss rods is not taken into account. It is assumed that the freights are moved only vertically. The fundamental frequency of natural oscillations is estimated from the Dunkerley formula by the values of partial frequencies. An analytical estimate is obtained by generalizing formulas obtained from a series of estimates for trusses with a consistently increasing number of panels. The stiffness of the truss was determined using the Mohr’s integral. The double lattice of the truss does not allow using the cross-section method; therefore, the forces in the rods were calculated (or estimated) in an analytical form using the method of cutting nodes with the compilation of a system of equilibrium equations simultaneously for all rods and three support reactions. The matrix of equilibrium equations was compiled in a software program written in the language of the Maple computer mathematics system based on the coordinates of the nodes and the values of the direction cosines of the forces. For a sequence of coefficients of the desired formula, linear homogeneous recurrent equations were found and solved by means of special operators of the Maple system. The resulting formula estimating the relationship between the fundamental frequency and the panels number has the form of a sixth degree polynomial with coefficients depending on the parity of the number of panels. The analytical result is compared with the smallest frequency obtained numerically from the solution of the problem of oscillation of the cargo system. It is shown that the main frequency, depending on the truss height, has an extremum. The method of generalizing particular solutions using the Maple system operators allowed authors to obtain and analyze a formula for a lower estimate of the fundamental frequency of oscillation of a truss model with an arbitrary number of panels. The resulting estimate can be used as a test for numerically obtained solutions. The formula is especially efficient for systems with a large number of panels; as numerical methods for their calculation are time-consuming require considerable time and have a tendency for accumulating rounding errors.

Gimaltdinov I.K., Kochanova E.Y. «Propagation of Detonation Waves in Bubbly Liquids in Suddenly Widening Channels» Акустический журнал, 65, № 3, с. pp. 246-252 (2019)

The propagation of detonation waves in a channel filled with a bubbly liquid that suddenly widens is investigated. Possible scenarios for the dynamics of detonation waves after their transition to the widening part of the channel are analyzed. The influence of the volume content of a combustible gas and the geometric parameters of the channel on the propagation and breakdown of the detonation wave has been established.

Zakhidov E.A., Kokhkharov A.M., Kuvondikov V.O., Nematov Sh.K., Tazhibaev I.I. «A Low-Frequency Photoacoustic Spectrometer with an RGB Light-Emitting Diode for Evaluating Photosynthetic Activity in Plant Leaves» Акустический журнал, 65, № 1, с. pp. 90-95 (2019)

A photoacoustic spectrometer based on a three-colored light-emitting diode (with peak emission wavelengths of 465, 525, and 640 nm) designed to determine the intensity of photosynthesis in different deep layers of plant leaves is described. The physical properties of the photoacoustic signal were studied at different wavelengths and light modulation frequencies. It was shown that the proposed spectrometer can be employed for quantitative evaluation of heat dissipation and photochemical assimilation of the absorbed light energy in this medium.

Wang Ping, Shi Yizhe, Jiang Jinyang, Kong Lu, Gong Zhihui «Generalized Sidelobe Canceller for Ultrasound Imaging based on Eigenvalue Decomposition» Акустический журнал, 65, № 1, с. pp. 123-131 (2019)

The improved generalized sidelobe canceller (GSC) based on eigenvalue decomposition beamforming technique for ultrasound imaging is proposed. Firstly, the signal subspace is obtained by performing eigenvalue decomposition on the covariance matrix of received data. Secondly, the weighting vector of GSC is divided into adaptive and non-adaptive two parts. Then the non-adaptive part is projected into the signal subspace to obtain a new steer vector. Subsequently, based on the orthogonal complementary space of the new steer vector, the blocking matrix is constructed. Finally, the weighting vector is updated by projecting the final weighting vector into the signal subspace. In order to verify the proposed algorithm, the simulations of the point targets and the cyst phantom were conducted in Field II. The experimental results indicate that the proposed method has better resolution and contrast ratio than the conventional algorithms. In addition, the algorithm is robust to noises. Furthermore, combining with coherence factor, the contrast ratio of the proposed algorithm can be further improved in comparison with a conventional GSC with coherence factor.

Tang Jun , Petrov P.S., Piao Shengchun , Kozitskiy S.B. «On the Method of Source Images for the Wedge Problem Solution in Ocean Acoustics: Some Corrections and Appendices» Акустический журнал, 64, № 2, с. pp. 225-236 (2018)

In this study the method of source images for the problem of sound propagation in a penetrable wedge [G. Deane and M. Buckingham, J. Acoust. Soc. Am. 93 (1993) 1319-1328] is revisited. This solution is very important three-dimensional (3D) benchmark in computational underwater acoustics, since a wedge bounded from above by the sea surface and overlying a sloping penetrable bottom is the simplest model of a shallow-sea waveguide near the coastline. The corrected formulae for the positions of the source images and bottom images are presented together with the explanation of their derivation. The problem of branch choice in the reflection coefficient is thoroughly discussed, and the corresponding explicit formulae are given. In addition, numerical validation of the proposed branch choice schemes and the resulting wedge problem solutions are presented. Finally, source images solution is computed for a series of examples with different ratios of shear and bulk moduli in the bottom. The interplay between the acoustic-elastic waves coupling and the horizontal refraction in the wedge is demonstrated.

Tyagi Kapil Dev, Kumar Arun, Bahl Rajendar, Singh Karmjeet «Experimental measurement of acoustic properties in snow» Акустический журнал, 63, № 3, с. 297-301 (2017)

This paper presents the results of field experiments done for the measurement of attenuation constant and speed of sound in the snow medium. The field experiments were conducted at two locations corresponding to relatively dry and wet snow. The main objective of our method is to overcome the potential limitations of the other methods. There are two major concerns: one is sound signal leakage and the other is the measurement need to be done within a same layer of snowpack. The ref lections from the boundaries will affect the measurements. In our experiments the transducers are kept far from the snowpack boundaries, so that there will be no likelihood of strong ref lected signals from the boundaries. These issues have not been addressed by the other researchers. This work adds to the measurement results of the attenuation constant and speed of sound in snow that are available in the research literature. It is found that sound signal attenuation greatly depends on the frequency of sound signal and wetness of snow.

Sharma Gaurav, Kumar Sushil, Singh Vivek «Design of Si–SiO₂ phoxonic crystal having defect layer for simultaneous sensing of biodiesel in a binary mixture of diesel through optical and acoustic waves» Акустический журнал, 63, № 2, с. pp. 158-167 (2017)

The potentiality of a phoxonic crystal for sensing of biodiesel in a binary mixture of diesel and biodiesel is theoretically investigated. Using the transfer matrix method, the transmission of acoustic and optical waves through a periodic one-dimensional crystal of Si–SiO₂ layers is studied. A pass band is created in the band gap region by introducing a cavity in the considered one-dimensional crystal structure. This pass band can also be considered as a defect mode, and it is found that its position is highly dependent on mole concentration of binary mixture of biodiesel and diesel present in the cavity. The sensitivity of the sensor for a binary mixture of biodiesel and diesel in the cavity with various mole concentrations is estimated. Simulated results provide a valuable guidance for designing a phoxonic crystal sensor consisting of a defect layer.

Mukhin N.V., Kutia M.M. «Thiophene determination in liquid hydrocarbons by in-line acoustic measurements» Известия высших учебных заведений России. Радиоэлектроника, 22, № 4, с. 82-88 (2019)

Introduction. Petroleum is a complex mixture of hydrocarbons. Sulphur is the most common heteroatom in petroleum and petroleum products. Its content in oil can reach 14%. The determination of sulphur in oil and its removal is of great importance, since sulphur compounds adversely affect the quality of petroleum products and pollute the environment. Desulphurization of hydrocarbons is important in the processing of petroleum products, which needs in usage of accurate and simple methods for the sulphur-containing components determination. Most of developed methods are difficult to apply for flow online analysis, which can create difficulties in using them to monitor the content of sulphur-containing heteroatomic components in real time. Acoustic sensors are one of the possible solutions. In term of sensing of flammable liquids, the use of the acoustic methods is attractive since the analyte is not a part of an electrical measuring circuit and it is only acoustically coupled that prevents an occurrence of a spark. Objective. The purpose of the work is to study the possibilities of online flow analysis of sulphur-containing heteroatomic components using acoustic measurements. The challenge is the development of a resonator system integrated with the pipe.Materials and methods. Thiophene and oil fraction with the boundary boiling point of 100–140 °C were used to prepare the mixtures. Thiophene is a representative of sulphur-containing components, which may be included in the composition of petroleum and its derivatives. Experimental measuring equipment includes impedance analyzer, a developed sensor structure integrated with a liquid-filled pipe, a pump and a tank with a measured liquid. A theoretical analysis of sensor structure was carried out on the basis of numerical simulation using COMSOL Multiphysics software. Results. The sensor structure was designed as a combination of 2D and 1D pipe periodic arrangements to achieve high Q-factor of acoustic resonance in the flow system. The eigenmodes of the sensor structure with a liquid analyte were carried out. The characteristic of sensor structure is determined. The sensor shows good sensitivity to the thiophene content with high resolution in-line analysis. This result is achieved by limiting the energy losses of acoustic resonance in radiation along the pipe by creating a periodic structure. Conclusion. The study of acoustic properties of solutions prepared on the basis of thiophene and oil fraction with boundary boiling point 100–140°C was performed. It shows that methods based on acoustic spectroscopy make it possible to accurately determine the concentration of heteroatomic components in gasoline mixtures, since the presence of heteroatomic components leads to a change in mechanical properties of liquid hydrocarbons mixtures. Possible applications for developed acoustic sensor are flow analysis for monitoring the quality of oil products.

Zakhidov E.A., Kokhkharov A.M., Kuvondikov V.O., Nematov Sh.K., Tazhibaev I.I. «A Low-Frequency Photoacoustic Spectrometer with an RGB Light-Emitting Diode for Evaluating Photosynthetic Activity in Plant Leaves» Акустический журнал, 65, № 1, с. pp. 90-95 (2019)

A photoacoustic spectrometer based on a three-colored light-emitting diode (with peak emission wavelengths of 465, 525, and 640 nm) designed to determine the intensity of photosynthesis in different deep layers of plant leaves is described. The physical properties of the photoacoustic signal were studied at different wavelengths and light modulation frequencies. It was shown that the proposed spectrometer can be employed for quantitative evaluation of heat dissipation and photochemical assimilation of the absorbed light energy in this medium.

Anisimkin V.I., Verona E., Kuznetsova A.S., Osipenko V.A. «Acoustic Wave Propagation Along Piezoelectric Plate Coated with Piezoelectric Films» Акустический журнал, 65, № 2, с. pp. 171-177 (2019)

A novel solid state structure consisting of piezoelectric plate sandwiched between two piezoelectric films is suggested as propagation medium for acoustic waves. Considering, as an example, quartz plate coated with AlN film and with AlN film together with ZnO film, the main characteristics of the Lamb and SH acoustic modes are numerically calculated and compared with each other. It is shown that i) the range of acoustic parameters achievable in structures is wider than that is for an uncoated plate, ii) generation of waves in the plate with one film is accomplished by 12 transducer configurations, while there are 32 configurations to excite the same waves in two film structure, iii) dispersion of the wave velocities and coupling constants depend on the mode order, mode type, film thickness, plate thickness, and transducer configuration. This property makes selection of appropriate modes more flexible. Results of calculations are partially verified experimentally.