Acoustical Physics最新文献

Recognition by adults of the psychoneurological state of children with autism spectrum disorders (ASD), n = 35, and typically developing (TD) children, n = 47, aged 5–14 years, was studied. A perceptual analysis was carried out, in which adult native Russian speakers (auditors) took part, n = 206. For perceptual analysis, test sequences (audio tests) were created containing words and phrases of children with ASD and TD children, selected from spontaneous speech recordings. The auditors were faced with the problem of determining the psychoneurological state of a child based on auditory perception: typical–atypical development. A spectrographic analysis of the speech material of children with ASD and TD children was carried out. The phrases of children with ASD are characterized by a lower speech rate compared to the phrases of TD children, as well as fewer words, longer duration of stressed and unstressed vowels in words, higher values of the frequency of the fundamental tone in the phrase, word, and stressed and unstressed vowels.

New protocols have been developed of biological tissue volumes with shock-wave bursts using trajectories uniformly filled with discrete foci within a given volume. Each focus was sonicated with a millisecond-long pulse, which immediately generated a single thermal lesion. In developing the most advantageous irradiation protocols, the effect of the source peak power at a constant time-averaged value, the distance between single foci, and geometry of the outer contour of the trajectory on the shape, volume, and thermal ablation rate was analyzed. It is shown that for an arbitrary geometry of the outer contour of a single-layer trajectory, the most advantageous is the saturation mode of the shock front amplitude at the array focus using a trajectory with a spatial step 1.5 times greater than the transverse size of the single lesion. To obtain thermal ablation volumes on the order of cubic centimeters, protocols have been suggested with layer-by-layer irradiation of tissue, which make it possible to accelerate the thermal ablation process by 2.5 times compared to protocols used in clinical practice. The advantage of the proposed protocols that use the shock-wave exposure is the ability to generate localized and predictable thermal lesion without using MRI temperature monitoring.

Numerical simulation of the aeroacoustic characteristics of a supersonic jet issuing from a Laval nozzle into space at rest at the design condition (Mach number M = 2) was carried out. The results of calculations using the large eddy simulation (LES) method are presented. The mean and fluctuation characteristics of the flow in the jet, as well as the characteristics of the jet noise in the far field, including its azimuthal composition, were obtained. The calculation results are compared with experimental data, and their satisfactory agreement is shown. It is concluded that there are various mechanisms of noise generation in the considered jet.

The features of the propagation of nonlinear pulsed acoustic disturbances in the atmosphere are considered. Data are presented on the experimental observation of shock front formation and the transition of a shock wave into a low-intensity acoustic wave with transformation of the pulse shape and broadening of the front at distances greater than 1000 km under both spherical and cylindrical propagation conditions. The influence of Kelvin–Helmholtz instability during rapid gas compression on the formation of the shock front structure is discussed. Under atmospheric conditions, such instability significantly affects dissipative processes in the air and forms the front of a nonlinear wave.

The article presents the results of a high-frequency experiment to detect and determine the bearing of a small-sized underwater noise sound source, carried out in shallow waters of the Black Sea coast. Noise emission from the source was received by three single vector–scalar receivers located at the bottom. Holographic processing was used to detect and determine the bearing of a moving underwater source against a background of heavy shipping in the water area of the experiment. Estimates of the input signal/noise ratio are given.

A computational and theoretical study of the properties of the well-known Chuprov waveguide invariant (CI) was carried out in a plane-parallel Pekeris waveguide. In contrast to earlier works, in which predominantly omnidirectional (monopole) sources were used as a source and sound pressure fields (scalar fields) were studied, in this work not only scalar, but also vector fields formed in the waveguide by directional-combined multipole sources with directivity in both horizontal and vertical planes are investigated. A differential equation has been obtained that makes it possible to fairly accurately calculate the CI values under different conditions of signal propagation and different depths of the sources and receivers. This makes it possible, in a simpler way than “total computer simulation,” to predict the invariance (stability) of the CI when both the hydrophysical conditions in the waveguide and the geometry of the experiment are varied. It is shown that the directivity of sources in the horizontal plane has virtually no effect on the properties of the CI, and the directivity in the vertical plane leads to a shift in the fan structure of the signal amplitude fields, but has little effect on the CI values. The properties of the fan structure change similarly when using vertical projections of the vibrational velocity vector: despite the fact that another analytical relation different from scalar fields is used to calculate the CI, the CI value is close to (1) at all frequencies and distances, except for those at which new modes or dislocations appear. At these frequencies and in these zones, alternating emissions with different signs and magnitudes occur. It is concluded that the stability of the CI allows the application of signal processing algorithms developed for scalar fields and nondirectional sources to vector–scalar fields generated, including with the use of directional sources.

The ability of the dolphin auditory system to recognize and classify noise signals according to certain invariant characteristics under the influence of noise interference and in conditions of spatial uncertainty of the simultaneous presentation of positive and negative signals was investigated. Bottlenose dolphins trained to differentiate such signals had to solve this problem in conditions simulating real sea conditions, when the perception of a useful noise signal occurs against a background of similar signals and against a noise interference background. First, noise signals were sequentially presented to the animal against a background of white masking noise. Subsequently, the dolphin had to identify a signal of a positive class from several simultaneously sounding sound sources. The animal’s performance was assessed at several specified noise interference levels. In this case, the actual noise interference was both white noise and simultaneously sounding negative signals. It has been shown that the efficiency and noise immunity of the dolphin’s auditory system depends on the degree of alternativeness of the spatial uncertainty of the simultaneous presentation of signals.