Acoustical Physics最新文献

Some results of a physical experiment on studying the evolution of an intense acoustic beam on a semiscreen obstacle are reported. The beam is formed by using a plane piezoceramic transducer with a center frequency of 2 MHz. The semiscreen obstacle is installed beyond the last diffraction maximum of the linear distribution of an acoustic field from the used transducer along the acoustic axis The transverse distribution of the nonlinear acoustic field is studied for different distances from the semiscreen obstacle. Initial acoustic beam intensities correspond to acoustic Reynolds numbers from 5 to 30. It is shown that evolution of the beam behind the obstacle is governed by cumulative diffraction and nonlinear effects. It is demonstrated that the transverse distribution of the acoustic field behind the obstacle strongly depends on the intensity of the beam incident on the obstacle. In particular, a strong dependence on the intensity of the incident beam is observed for the position of diffraction maxima in the transverse distribution of the acoustic beam behind the semiscreen obstacle. The effect related with the appearance of additional extrema in the transverse field distribution at different harmonics is revealed. Numerical simulation based on the Khokhlov–Zabolotskaya–Kuznetsov equation is carried out with results confirmed by experimental data.

Spectral proper orthogonal decomposition (SPOD) is proposed for identification of the multipole structure of aeroacoustic noise sources from far-field measurements. The method is verified via tests with point multipoles and validated using experimental data on flow-induced cylinder noise and turbulent jet noise.

The International Organization for Standardization (ISO) introduced the term “soundscape,” which defined the latter as “an acoustic environment perceived or understood by a person/people in context.” It proposed methods for quantitatively assessing human emotional reactions to a sound environment. In one of the methods, such reactions were represented as coordinates on the Pleasantness–Eventfulness plane. The pleasantness coordinate assessed how pleasant the environment was for the subject at the time of the examination, i.e., the properties of the subject, and the eventfulness coordinate assessed how eventful the environment was, i.e., the properties of the environment. The aim of this study was to verify the standard ISO method. Therefore, an audiovisual examination of the environment was carried out in different locations; pleasantness and eventfulness coordinates were calculated; acoustic and psychoacoustic characteristics of the environment were recorded and calculated, and the latter were then compared with the characteristics of soundscapes (or pleasantness and eventfulness coordinates). It was shown that a sound environment with physical characteristics higher than established sanitary standards may well be pleasant for a person. The results confirmed the validity, informativeness, and integrity of the method for assessing soundscapes, as well as its accessibility for nonprofessional experts. The characteristics of soundscapes can be used for engineering design of the sound environment of urban areas.

A comparative analysis has been performed on the morphology and some hearing mechanisms of the evolutionary new external ears of bottlenose dolphin (Tursiops truncatus) and human ears. It has been established that the role of external hearing canals in dolphins is played by corresponding mental foramens (MF), mandibular canals (MC), and soft tissues (ST) filling them. It has been demonstrated that the hearing canals of dolphins are maximally ported out to the tip of the rostrum towards echos and sounds reflected from underwater objects, in contrast to the hearing canals of humans, which are located on the left and right sides of the head. The major factors influencing the mechanisms of the formation of unique features in the spatial sound localization of dolphins are asymmetry in the architecture of their hearing canals, rostrum, and skull. However, for humans, these mechanisms are caused by the symmetric location of hearing canals on the left and right sides of the head. The morphology of the external ears of dolphins is adapted to utilize the destructive interference of reflected coherent interferences with the purpose of improving the signal/reflected interferences ratio. In general, the specific features of dolphin and human hearing cause fundamental distinctions in the morphology and auditory mechanisms of their external ears.

The possibility of changing the efficiency of nuclear spin–phonon coupling by NMR methods using the example of a NaF crystal in a wide temperature range is investigated. To suppress nuclear spin-lattice relaxation involving paramagnetic centers, continuous magnetic saturation at a single Larmor frequency is used instead of acoustic saturation of the ²³Na NMR signal at a double frequency. The influence of the (i) color centers induced by gamma irradiation and (ii) temperature on the separation of spin–phonon coupling mechanisms is studied. No suppression of impurity relaxation is observed for ¹⁹F dipole nuclei. It is shown that the suggested magnetic saturation technique for complete or partial shutdown of impurity relaxation of quadrupole nuclei can be implemented on commercial pulse NMR spectrometers.