Acoustic Institute named after NN Andreev

An elastic medium with inclusions that are small compared to the sound wavelength and differ in density is considered. If the inclusions are resonators that respond equally to the influence of waves coming from different directions, then the effective density of the medium in a certain frequency band becomes negative. If the direction of the dipole moment of the resonators is fixed, then the medium with inclusions has an anisotropic effective density. The Helmholtz equation for such a medium was obtained, and the field of a point source was studied.

This investigation relates to the production of materials with noiseproof and vibration-absorbing properties, in the manufacturing of which a number of by-products are formed that require for safe disposal. When solving the production problems connected with wastewater treatment from toxicants, the concentration of which exceeds permissible values, it is proposed to use structured materials based on silicon dioxide as an adsorbent. In the course of conducting research, two experimental samples with a highly developed surface containing an extensive network of pores have been obtained and tested. The experimental testing of adsorbents has shown that such adsorbents are able to provide the removal of toxicants up to attaining a safe concentration level thereof.

A lot of worship spaces with acoustic cavities of different sizes and forms are known today due to a number of reviews and studies published last decades.Pots, jars and other vessels were used in church architecture of the Middle Ages in many European countries.During this period the practice of using such devices was widespread in Russia as well, but the most impressive heritage was given by the Pskov architectural tradition.The churches built there from the 13 th to 16 th centuries were equipped with hundreds of the acoustic vessels.For various reasons, many churches have not survived to this day, but a significant number of them still exists.This paper reviews sixteen Orthodox churches in Pskov, which were built from 1243 till 1586 and have a lot of acoustic vessels.The biggest number of vessels is observed in the Peter and Paul Church.In spite of its small volume which is only about 1300 m 3 , there are 326 vessels installed in the drum, pendentives and walls.Ten churches have more than 100 vessels, the smallest number is 42.Description of the churches and analysis of the location of the vessels on inner surfaces are presented.

Рассмотрены некоторые свидетельства в пользу того, что недавно обнаруженная двойная черная дыра в центре галактики UGC 4211 — возможно два близко расположенных входа в одну и ту же кротовую нору.

The provocation of the hydroacoustic communication interaction of Tursiops truncatus dolphins based on cognitive empathy showed that they use packets of ultrashort pulses (USPs) in the process of “dialogue”. The duration of bursts varies from 40 ms to 3000 ms with modulation of the interval between USPs from ~1 to ~120 ms and pauses between bursts. The interval modulation pattern is structured using various modulation laws. The communication signals were obtained in an experiment with theparticipation of three animals, who knew the main task of sequential acoustic differentiation of two objective stimuli. The impetus for hydroacoustic interaction is the resolution of uncertainty when teaching the respondent the inverse differentiation problem. This generates emotional empathy in observers and provokes vocalization between individuals. The advantages and disadvantages of methodological methods of provoking hydroacoustic interaction are considered in detail, starting the process of cognitive empathy. In the method under consideration, echolocation and communication signals are spaced apart in time and space, which allows them to be uniquely identified.

Abstract The variability of the impulse activity of neurons in the temporal cortex of an unanesthetized cat was studied in the absence of special sound dampening and in the presence of reverberation. Registration was carried out both in silence and under the influence of various intense sounds coming from the frontal direction. Almost all cells had background activity. Both background and evoked impulse activity were characterized by high bursting and properties inherent in fractal point time processes. The dynamics of impulses over long time intervals of background activity and the nature of variations in the number of impulses per presentation were characterized by the Fano and Hurst methods. A high variability was revealed not only in the background, but also in the evoked activity, which was especially pronounced outside the primary zone A1.It can be assumed that dynamic changes in the firing of cortical units in unanesthetized state of the animal reflect the permanent evolution of the biological neural network in the process of analyzing incoming information and forming traces of short-term memory.KeywordsAuditory cortexNeural activityVariability Hurst indexFano factorFractalityAnterior ectosylvian sulcus

On the northeastern shelf of the Black Sea in 2010, a tomographic experiment was carried out on the counterpropagation of phase-shift keyed acoustic signals. During the day, the time responses of the medium were measured during the emission and reception of high-frequency complex phase-shift keyed signals from three bottom-moored transceivers located at the corners of an equilateral triangle with sides of about 1100 m. The transceivers were at a distance of >2 km from Golubaya Bay at a depth of about 40 m. Nearby, a thermistor chain was moored to record internal waves. Based on the data on the temporal variability of the responses of the medium to acoustic signals, information about the internal waves present in the water area was reconstructed using the method of consistent time responses. A temporal sampling of the vertical displacements of the thermocline was obtained, in which short-period waves with a height of 0.5–1 m and a period from 5 to 15–20 min were found. Comparison of acoustic measurements with independent contact measurements of internal waves revealed their good mutual agreement. On the whole, the results of the acoustic experiment showed the possibility of successfully using acoustic tomography to study the dynamics of waters for shallow-water conditions.

The article presents the results of applying the signal time reversal method in the ultrasound (~130 kHz) under strong spot heating conditions (>250°С) and deformation of the investigated sample—a steel plate. It is shown that the distortions of the time-reversed signal during propagation, caused by changes in the sample properties, can be significantly reduced by reducing the duration of the processed signals and by using several receivers.

Results are presented from an experimental study of the propagation of acoustic pulses on the shallow marine shelf of the Black Sea and a coastal wedge. Signals associated with bathymetric refraction are analyzed. Short-period signal fluctuations on a Black Sea coastal wedge along stationary acoustic tracks with a mean bottom slope of ~25° are studied. The spectra and characteristic periods of fluctuations in the amplitude, azimuthal angles, angles of slide, and arrival times of pulsed signals are determined. The main reasons for fluctuations in the characteristics of signals under conditions of pronounced horizontal refraction with changing bathymetric characteristics are discussed.