A theory of acousto–optic interaction (AOI) in anisotropic medium, taking into account absorption of electromagnetic waves and attenuation of acoustic waves, has been developed. Expressions for optimal length and bandwidth of the AOI were derived. A non–reciprocal effect inherent only in the backward collinear diffraction was discovered.
Show AbstractA method to determine optimal values of acousto-optic (АО) figure of merit was developed. Its advantages are clarity and high performance. Results can be used for development high-efficient AO devices based on optically isotropic media.
Show AbstractIn this paper different criteria of thermal ablation induced by high intensity focused ultrasound in clinically significant volumes of biological tissue were compared. Sonications using a multi-element ultrasound array and various nonlinear focusing regimes were considered in numerical experiment. Sonication of tissue was maintained until thermal dose reached a threshold value at the circle of a certain radius. The threshold temperature was chosen so that the sonication stopped at the same time when using the criteria of temperature or dose. Threshold temperatures equivalent to the thermal dose threshold achieved at the end of the heating were obtained. Volumes of thermal lesions in tissue were calculated using both the criteria of thermal dose and temperature. It was shown that the use of the threshold temperature criterion corresponded with good accuracy to the thermal dose criterion in case of the uniform heating of the tissue volume.
Show AbstractA numerical algorithm for calculating ultrasound fields radiated from axially symmetric focused sources was developed on the basis of a wide-angle parabolic approximation of the Helmholtz equation. A numerical solution for the field of an axially symmetric spherical radiator with an aperture of a = 5cm, focal length F = 9cm, and the frequency f = 1MHz was obtained. The solution was compared to those obtained using the full diffraction formulation and with conventional parabolic equation. The results showed that the relative error in pressure amplitude at the focus was 1–2% for a wide-angle parabolic approximation and 10–12% for the conventional parabolic approximation comparing to the exact Rayleigh integral solution. Calculation time for a wide-angle model was comparable to conventional parabolic model, and was an order of magnitude less than calculating the exact solution using the Rayleigh integral.
Show AbstractThe experiment of the sound propagation in a shallow pond in a natural environment was made. The pond surface was covered with a layer of ice. The signals were recorded synchronously by the system of four vertical antennas located at different distances from the source. The waves propagating in the water layer and in the pond bottom were detected and its velocities were obtained.
Show AbstractOne of the information sources about physical properties of the inhomogeneous medium is a dispersion of surface wave velocity, which amplitude decays exponentially at a depth about the wavelength. In the case of shallow water for the characteristics of the deep bottom recovery the registration of the «bottom» wave propagating along the boundary «elastic bottom–water layer» is required. For this wave registration usually ocean bottom systems are used. The experimental data are accumulated in the memory card that is removed after the measurement with the sensor, or data is transmitted through the satellite transceiver to surface communication channels. In the case of sea covered with ice use of these systems significantly hampered. This paper, based on experimental data shows that the time-frequency analysis of the cross-correlation function of signals, recorded by wideband sensors located on the surface of the ice, allows you to select in the received signal information on the propagation time of the waves between the bottom sensors. The obtained result allows speaking about the possibility of constructing of a sounding of deep inhomogeneous structures in the presence of ice cover with significantly reduced requirements on the practical implementation of this approach.
Show AbstractTwo commercial sound absorbing materials and also a material made of thin tubes absorbing sound due to viscosity are studied using a simple method of acoustical interferometer and a theoretical description of these materials is also made.
Show AbstractResults of numerical modeling the functional algorithm are presented, which allows to reconstruct acoustic inhomogeneities with scalar and vector constituents. The resulting functional solution of the inverse problem is mathematically rigorous for a wide range of scatterers. On the other hand, the reconstruction results for the vector of flow currents are presented which were obtained from experimental data measured by the ultrasonic tomograph. These data are processed by the weighted additive accumulation followed by a space–correlation comparison of image fragments.
Show AbstractThe purpose of this study is to investigate the possible mechanisms of extreme waves’ generation during degeneration of long sinusoidal (tidal) waves in the framework of the Gardner equation. A statistical analysis of the solitons ensemble formed during the evolution of the undular bore in various possible environmental conditions is done.
Show AbstractWe study some peculiarities of the small dispersion limit for the Gardner equation with positive and negative sign of cubic nonlinear term and positive quadratic nonlinear term by numerical modeling of evolution of long bell–shaped pulse with a polarity, opposite to the sign of the quadratic nonlinearity. A statistical and spectral analysis of wave fields is carried out.
Show AbstractThe wave motion into two-layer conducting liquid with insoluble film of surfactant on the upper electrically charged surface has been investigated. The role of surfactant and charge and also variation of interfacial tension at different mode of wave motion have been considered. Mutual influence of different effects has been analyzed.
Show AbstractThere are behavior of liquid particles of two immiscible moving fluids is considered. Curious patterns of liquid particles motion are discovered. It is shown that the character of the individual fluid particle motion significant depends on the relative velocity of the contact fluids.
Show AbstractThe work investigates the mechanisms of influence of internal waves on the transport of chlorophyll-a. Revealed the structure of the velocity field in the presence of internal waves interacting with the jet at the thermocline, the drift current and density flow. The regularities of influence of internal waves on the distribution of chlorophyll-a. The resulting dependence of the concentration of chlorophyll-a in an active layer of the height of the internal wave. Discovered and are presented analytically the dependence of the concentration of chlorophyll-a from the phase velocity of the internal wave and the concentration of suspended solids.
Show AbstractThe nonlinear dynamic and chaos in the system of Rydberg atom chain is studied. Chaotic dynamics is revealed. The method for suppression of chaos by external parametric impact in the system is offered.
Show AbstractWe have studied the electrical activity observed in left and right hippocampuses of rats being under anaesthesia by means of continuous wavelet transform with complex basis. We have obtained the distributions of lengths of the synchronous behavior between generators of local field potentials in right and left parts of hypothalamus of rodents.
Show AbstractIn this paper, we consider the interaction between the ensembles of nonlinear elements, demonstrated both the chimera state and coherent or incoherent state, in the framework of a multilayer network model. We show that the interaction between a layer, which demonstrates chimera state, and the layer of completely coherent or incoherent oscillators, leads in case of the weak interlayer coupling, to the suppression of chimera and transition to the coherent or incoherent state, and in case of the strong interlayer coupling - to the excitation of chimera state from both coherent or incoherent oscillators.
Show AbstractIn this paper we study the interaction between semiconductor superlattices, working in the non-stationary charge transport regime, and coupled via the quality resonant circuit. We found that the connection of the second superlattice significantly affects the amplitude-frequency characteristics of the system, the areas of chaotic generation are discovered.
Show AbstractIn this paper, the process of formation of high-temperature entangled states in a system of two coupled quantum parametric oscillators with a partially coherent pumping is considered. It is shown that the presence of noise in the pump has a significant impact on the dynamics of the system. It imposes a limit on the temperature at which the entangled states are formed, determines the lifetime of entanglement in the system
Show AbstractNeurocognitive experimental works have been carried out. We construct one-dimensional theoretical model depended on the objective ambiguous parameter (intensity of Necker cube face). This model is demonstrated its good agreement with experimental results. In addition, on the basis of registered volunteers EEG data evaluation were conducted and the parallels between the theoretical models and objective data registered in the course of psychological experiments on the perception of ambiguous images.
Show AbstractThe semiconductor superlattice is a compound nanostructures is consist on the several thin layers of different semiconductor materials, that can be used for generation and control of the high-frequency oscillations. At the last time to be of interest the investigation of this structure in the context of the nonlinear dynamics. In this work we consider changes of the electron dynamic is defined the current characterizations for different shape of the perturbation of the doping concentration.
Show AbstractIn this paper we consider two laterally coupled YIG waveguide with ferroelectric load. The possibility of dual control of coupling length in the structure was shown.
Show AbstractThis report shows the results of investigation of the spin-waves discrete diffraction in the laterally coupled planar YIG waveguide array by numerical analysis and Brillouin light scattering (BLS) spectroscopy.
Show AbstractIn this paper we consider a structure consisting of two laterally related YIG–waveguide, which can be used as basic elements to create a variety of functional devices magnetoelectronic: waveguides, filters, couplers.
Show AbstractThe approach to parallel implementation of low-frequency PIC–algorithms is proposed, taking into account peculiarity of the nonradiative (Darwin, magnetoinduction) field approximation. Its advantages and possible constrains.
Show AbstractThe possibilities and features of the some methods of calculation of the scaling characteristics of radiation interacting with objects, which have obvious and hidden fractal characteristics, are analyzed. The data on the relationship of the scaling parameters of objects and probing beams are presented.
Show AbstractIn the simulation of physical processes and phenomena in radio physics, optics, we propose to use Finite Sampling Theorem (FST) instead theorem of Wiener–Kotelnikov and methods based on the difference schemes. FST operations are compatible with the convolution, analytical calculations, estimation of multiple integrals.
Show AbstractModeling of the torsion system by parameters of the suspension wire and the spherical mass on it is carried out. The viscous air friction limits the possibilities of the method. Maximum Q–factor is limited by internal friction in the wire is determined.
Show AbstractThe solution to a diffraction problem of the linearly polarized wave by the flat nanoscaled particle in the medium with a substrate is constructed on the basis of the modified discrete sources method hybrid scheme. The possibility of applying the developed approach to study resonant properties of plasmonic nanoparticles is considered.
Show AbstractMathematical model for rectangular waveguide with impedance wall on which impedance Schukin–Leontovich boundary conditions are implemented is considered. Using these boundary conditions complete electromagnetic field in the waveguide is not divided into TE and TM fields and hybrids modes have to be taken into account. A new basis to represent components of complete electromagnetic field of a rectangular waveguide is suggested using witch impedance boundary conditions are satisfied exactly. Stiff system ODEs for amplitudes of this representation is a result.
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