The field of a surface acoustic wave in the system "viscous fluid layer - elastic substrate" is calculated taking into account the shear components in the fluid. The dispersion equation was used to calculate the amplitudes of the surface wave. The radiation pressure arising in a viscous fluid from the side of a standing surface wave and acting on an element of its volume due to the nonlinearity of the equations of motion, and the acoustic flows created by it are calculated. It is shown that taking viscosity into account changes the spatial distribution of radiation pressure. Attenuation of the wave causes an additional tendency for the collection of suspended particles in the center of the system. Shear components lead to significant gradients of radiation pressure near the interface between the media. They play a decisive role in the formation of ordered ensembles of suspended particles at the last stage of the self-organization process.
Show AbstractA topological insulator is a material that simultaneously exhibits the properties of a conductor on the surface and an insulator in volume. Rudner's game is a simplified model of a topological insulator, experimentally implemented on two-dimensional photonic lattices and described as a cellular automaton similar to Conway's game of life. A three-color cellular automaton is a regular lattice of cells. Each cell takes one of three colors according to the specified cell recoloring rule. In this work, two colors of the cellular automaton correspond to the absence and presence of a photon in the resonator, and the third color corresponds to the boundary of the region. The Rudner game is generalized to the case of a three-dimensional array of optical cavities and the defining properties of a topological insulator are demonstrated. A class of cellular automata is introduced that preserve the boundary and the number of photons, as well as zero group velocity for photons far from the surface. Physical realizations are expected in photonics, electronics, mechanics, and acoustics.
Show AbstractThe influence of the symmetrical bending of the profile of a linear antenna array along the arc of a parabola on its radiation pattern, efficiency, and consistency with the feeder is studied. The effects are demonstrated on the example of an 11-element model of an equidistant antenna array with different inter-element distances, for which an electrodynamic problem with boundary conditions for the electric and magnetic field vectors is numerically solved. The lattice was bent at a constant length along the arc of the parabola. Half of the angle of the aperture relative to the focus of the parabola is selected as the parameter that characterizes the profile. The study was carried out with in-phase equal-amplitude power supply of the grid elements. Estimates of the values of the best matching frequency and the best matching frequency offset when changing the bending profile are obtained, the dependence of the efficiency coefficient on the bending parameter, the horizontal and vertical cross-sections of the radiation patterns are constructed. The results show that with a decrease in the focal length, the efficiency is stable, while it deteriorates by no more than 0.1 dB, and the nature of the radiation changes from unidirectional to conical. The frequency parameters and the consistency with the feeder show a stable behavior when the profile is bent, but they change significantly when the inter-element distance changes.
Show AbstractThis article examines the effect of object position on cognitive evoked potentials observed in subjects with chronic pain. Chronic pain often causes cognitive depression. The experiment consisted of passing small cognitive tests, where the subject assessed the number of squares presented on the left or right side of the screen, or in the center. A simple method is proposed for automatic identification of the main components of the cognitive evoked potential, based on the identification of extrema and the assessment of the amplitudes of the main components of the cognitive evoked potential. Examples of analysis of individual characteristics for several subjects are shown. The maximum difference between the adjacent main components of the evoked potential lies, as a rule, on the central axis, but can be located in the subjects in the frontal, parietal, or occipital lobes. For two subjects, the individual characteristics of the main components of the cognitive evoked potential were shown at different positions of the object on the screen during the performance of the cognitive test. For one, the evoked potentials change when the stimulus is located on the left side of the screen. For the second, large changes are observed when the stimulus is located on the right side of the screen. It is extremely important to know these characteristics of the subjects when setting up automated brain-computer interfaces.
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