The results of physical and numerical modeling of the propagation of shear waves in soft biological tissues (elastography of shear wave) are presented. Physical modeling was carried out on a Verasonics acoustic system with a phantom imitating a skeletal muscle. Numerical modeling of shear waves is performed in the toolbox k-Wave
Show AbstractThe regularities of a mass-transfer caused by a Stokes’s wave package propagating at a horizontal interface of two environments are investigated analytically asymptotically for a pair of inviscid immiscible fluids which are shifting relate to each other.
Show AbstractThe paper analyzes the parameters of the process of formation of flows and removal of surface-active substances (SAS) under the action of bubble flow, common to natural and technical systems, as well as existing methods for studying these parameters. The description of the developed experimental setup for determining the parameters of the bubble flow by optical and acoustic methods is given. The methods of laboratory modeling of processes of SAS removal by bubbles with the use of modern technical means and new approaches are developed.
Show AbstractIn present work we studied extreme events that occur on elecroencephalogram of rodents with induced stroke. These events were registered as epileptic seizures with form of sudden high-amplitude oscillations, that emerge during first 2-3 hours after the stroke. Time-frequency structure analysis of electroencephalogram showed, that extreme events manifest themselves as sharp increase in wavelet energy distribution for characteristic frequency range. At the same time, wavelet energy in the rest part of spectrum remained unchanged. Revealed distinct features of extreme events were used for their detection on electroencephalogram. Quantification of extreme behaviour was held with help of construction of probability distribution functions for wavelet energy maxima and their approximation with different analitical distribution functions.
Show AbstractIn this paper, we describe the results of application a mathematical method to analyze multidimensional time series to identify changes in functional connections in the human brain that occur while viewing educational video lectures. This mathematical method is based on the establishment of mutual dependence of processes in terms of their conditional probability and is known in the literature as a Recurrent Measure of Dependence. Multichannel signals of electrical activity of the human brain were obtained during a series of neurophysiological experiments on the registration of electroencephalograms (EEG). With the application of a mathematical technique, qualitative changes in the dynamics of the brain were shown in the learning process in comparison with the background activity, caused by activation of the processes of perception and processing of external visual information.
Show AbstractWe have proposed brain-computer interface (BCI) for the estimation of the brain response on the presented visual tasks. Proposed BCI is based on the EEG recorder Encephalan-EEGR-19/26 (Medicom MTD, Russia) supplemented by a special home-made developed acquisition software. BCI is tested during experimental session while subject is perceiving the bistable visual stimuli and classifying them according to the interpretation. We have subjected the participant to the different external conditions and observed the significant decrease in the response, associated with the perceiving the bistable visual stimuli, during the presence of distraction. Based on the obtained results we have proposed possibility to use of BCI for estimation of the human alertness during solving the tasks required substantial visual attention.
Show AbstractThe experimental results of observation of frequency spectra of high-power semiconductor lasers are presented. The reasons for the transformation of laser spectra during long-term time operation are discussed. Estimates of changes in the optical parameters of the laser, which change during its slow degradation and determine the type of its frequency spectrum, are given.
Show AbstractThe speech analysis and approximation algorithm based on the continuous wavelet transform was created. In the current work, audiofiles from the Zuiga Mizuki voice bank were analised and some of them (namely vowel sound files) were synthesised using the suggested algorithm.
Show AbstractA mathematical model of noble metal nanoparticle excitation by point charge in uniform straight motion is considered in homogeneous medium. Nanoparticle size is assumed to be less than $10$nm. The problem solution (EELS spectrum) is constructed with the semi-analytical Discrete Sources Method taking into account the nonlocal effect.
Show AbstractThe scaling properties of the spectral characteristics of aperiodic multilayer systems with metamaterials are considered. The role of dispersion effects and phase compensation effects is determined by changing the geometry of the layers and the transition to quasicrystalline models of approximants.
Show AbstractThe density of plasma excitations in a graphene superlattice on a banded substrate in the presence of a strong static electric field is investigated. Calculations are performed on the basis of the quantum theory of plasma waves in the random phase approximation with allowance for Umklapp processes. The action of a strong electric field leads to a decrease in the frequency of plasma waves, to the appearance of collisionless damping (Landau damping) and to a shift in the peak of the density of plasma excitations toward low frequencies. Collective excitations are overlapped by single-particle excitations in the low-energy region, which will lead to a difference between theoretical and experimental data in the initial energy region.
Show AbstractAn experimental study and a numerical simulation of the propagation of laser radiation with wavelengths of 1064 nm and 532 nm in disordered media have been carried out. The samples were suspensions of rutile in DMSO with different volume fraction of scatterers. The effect of the volume fraction of scatterers in the suspension on the photon lifetime in the medium has been investigated. To determine the influence of the volume fraction of scatterers on the Raman efficiency Raman spectroscopy was carried out. It has been shown that at large volume fraction of scatterers decreases the volume of light-matter interaction. The maximum increase in the Raman signal achieved in suspensions is fourfold.
Show AbstractThis paper presents dielectric permittivity spectra of monohydric alcohols reconstructed in the frequency range of 500 Hz to 10 THz. The widely acknowledged method of dielectric spectroscopy has been employed, revealing the molecular dynamics of monohydric alcohols and their solutions in water by means of interpretation of results of ultra-broadband spectra measurements. Model spectra are presented using sums of Debye functions. The paper identifies Debye relaxation parameters in various frequency ranges and provides analysis of spectra patterns based on temperature and concentration. The study demonstrates exponential dependence on reciprocal temperature for each of the approximation parameters and their respective activation energies. Dynamic permittivity model was employed in analysis of alcohol spectra for the first time, making it possible to track physical processes with different timing taking place in tested media. The study identifies fields of high and low frequency permittivity without dispersion, analyzing permittivity patterns based on temperature. Comparison of the observed values of activation energies of high and low frequency permittivity indicates that they have the same order. Basic principles of the probability theory and mathematical statistics, numerical approximation and optimization of functions have been used in analysis of results of the study.
Show AbstractIn this paper, a new scheme of a microwave device of the vircator type is proposed, in which the mechanisms of generation of electromagnetic radiation in the upper range of microwave spectra (of the order of 30 GHz) and the amplification of induced oscillations due to interaction with a periodic electromagnetic system of a photonic crystal are combined. In the framework of numerical electromagnetic three-dimensional modeling by the particle-in-cell method, the efficiency of such an interaction is shown in the form of an increase in the amplitude, which corresponds to the enhancement of a particular type of fast vortex waves arising in electron beams as a result of the beam-plasma instability in the absence of ions.
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