The method of identifying the direction of the coupling between oscillators based on the simulation of phase dynamics of weakly coupled and weakly noisy periodic processes is used to determine the direction of the coupling between time series extracted from biological signals. Neuronal activity, arterial pressure and respiratory rate of anesthetized rats were used as initial data. Various options for the direction of the coupling between the analyzed time series were revealed.

The processes of heat removal from multijunction solar cells on a germanium substrate to AlN ceramics through a solder layer were studied by thermal wave photodeflection methods. Two types lead-free solder based on SnBi and SnAgCu were used under various pressure soldering conditions. The thermal conductivity and thermal resistance of the solder layers are compared. It is shown that the thermal conductivities of the solder layers differ from the reference data for the corresponding metal alloys, and in some cases may depend on the pressure during the brazing process.

The task is to determine the indices of phase synchronization between biological data extracted from neuronal activity and fluctuations in blood pressure and respiration, based on the calculation of instantaneous frequencies and phases using the synchrosqueezed wavelet analysis. Differences in synchronization indices between the analyzed data in two groups of rats (the control group and the group with experimentally induced colitis) were revealed. Pain exposure was found to be associated with frequency adjustment of the variability of the neuronal activity or the blood pressure, followed by the onset of phase synchronization.

The effect of misaligned mechanical stresses on the excitation of ultrasonic vibrations by focused laser radiation near a small-diameter hole in aluminum alloy is investigated. The analysis of the behavior of the signal at various mutual angles and values of two uniaxial stresses is carried out. It is shown that at certain angles under the action of mechanical stresses, not only the contrast of laser ultrasound images changes, but also their rotation as a whole relative to the center of the hole can occur. The possibility of disappearance of the linear component of laser ultrasonic signals at certain characteristics of stress and appearance of a nonlinear component is also demonstrated.

This paper is a review of recent applications of a laser photothermal mirage technique for sensing and measuring the thermal resistance of joint layers in modern electronic devices. A straightforward theoretical model of the interfacial thermal resistance based on the formation of a thin intermediate layer between jointed solids is described. It was experimentally shown that thermal properties of solder layers cannot be evaluated simply on the base of averaging the thermal properties of solder components. The review presents the laser thermal wave methodology for measuring thermal parameters of soldered and adhesively bonded joints. The developed theoretical model makes it possible to carry out a quantitative estimation of local thermal conductivities of joints and their thermal resistances by fitting theoretical results with experimental data obtained by the laser beam deflection method. The joints made with lead-containing and lead-free solders were studied. The anomalous distribution of thermal properties in the solder layer is explained by the diffusion of various atoms detected by energy dispersive X-ray spectroscopy. The laser beam deflection method made it possible to reveal a strong influence of the surface pretreatment quality on the interfacial thermal resistance.

A theoretical model for the formation of ultrasonic signals in metallic microcrystalline rods taking into account the metastable behavior of their defective states is proposed. The influence of metastable states of the defective structure of samples on the features of changes in their resonant frequencies in ultrasonic experiments of fast dynamics is analyzed. The increase in the Young's modulus and the dynamics of changes in resonant vibrations of rods made of aluminum alloy D16T under conditions of free relaxation are explained. Based on the results obtained, the concentration of metastable defects was estimated.

A theoretical model for the formation of ultrasonic signals in metallic microcrystalline rods taking into account the metastable behavior of their defective states is proposed. The influence of metastable states of the defective structure of samples on the features of changes in their resonant frequencies in ultrasonic experiments of fast dynamics is analyzed. The decrease in Young’s modulus in such processes is explained. The correspondence between theoretical and experimental data is demonstrated for the example of resonant acoustic vibrations of rods made of aluminum alloy D16.

The task is to determine the indices of phase synchronization between biological data extracted from neuronal activity and fluctuations in blood pressure and respiration, based on the calculation of instantaneous frequencies and phases using the synchrosqueezed wavelet analysis.. Differences in synchronization indices between the analyzed data in two groups of rats (the control group and the group with experimentally induced colitis) were revealed. Pain exposure was found to be associated with frequency adjustment of the variability of the neuronal activity or the blood pressure, followed by the onset of phase synchronization.

We applied methods for determining the recurrence based phase synchronization index and the coupling directionality based on conditional probabilities of recurrence to analyze the direction of coupling and synchronization of time series obtained from experimental data. The activity of brain neurons, fluctuations in arterial blood pressure, and the respiratory rhythm of anesthetized rats were used as experimental data. For the first time, variants of changing the direction of the coupling between the analyzed time series before and during pain exposure were revealed. The relationship of pain exposure with the adjustment of the frequency of the variability of neuron activity of the brain to the frequency of the variability of arterial blood pressure or with the adjustment of the frequency of the variability of blood pressure to the respiratory rhythm with the subsequent occurrence of phase synchronization has been established.

A theoretical model for the formation of ultrasonic signals in metallic microcrystalline rods taking into account the metastable behavior of their defective states is proposed. The influence of metastable states of the defective structure of samples on the features of changes in their resonant frequencies in ultrasonic experiments of fast dynamics is analyzed. The increase in the Young’s modulus and the dynamics of changes in resonant vibrations of rods made of aluminum alloy D16T under conditions of free relaxation are explained. Based on the results obtained, the concentration of metastable defects was estimated.

The processes of heat removal from multijunction solar cells on a germanium substrate to AlN ceramics through a solder layer were studied by thermal wave photodeflection methods. Two types lead-free solder based on SnBi and SnAgCu were used under various pressure soldering conditions. The thermal conductivity and thermal resistance of the solder layers are compared. It is shown that the thermal conductivities of the solder layers differ from the reference data for the corresponding metal alloys, and in some cases may depend on the pressure during the brazing process.

Исследовано влияние несоосных механических напряжений на возбуждение ультразвуковых колебаний сфокусированным лазерным излучением вблизи отверстий малого диаметра в сплаве алюминия. Проведен анализ поведения сигнала при различных взаимных углах и величинах двух одноосных напряжений. Показано, что при определенных углах под действием механических напряжений не только происходит изменение контраста лазерных ультразвуковых изображений, но и может происходить их поворот как целого относительно центра отверстия. Также продемонстрирована возможность исчезновения линейной составляющей лазерных ультразвуковых сигналов при определенных характеристиках напряжений и появления нелинейной составляющей. Ключевые слова: диагностика, неразрушающий контроль, механические напряжения, лазерный ультразвук.

Differences in phase synchronization between intermittent photic stimulation and electrical activity of the brain recorded as electroencephalographic (EEG) patterns were studied in two groups of patients with chronically elevated arterial pressure with and without cognitive impairment. It was found that the parameters of phase synchronization calculated using synchrosqueezed wavelet transform of the light stimulus and the EEG pattern can be used as neurophysiological markers of moderate cognitive impairment.

A theoretical model for the formation of ultrasonic signals in metallic microcrystalline rods taking into account the metastable behavior of their defective states is proposed. The influence of metastable states of the defective structure of samples on the features of changes in their resonant frequencies in ultrasonic experiments of fast dynamics is analyzed. The decrease in Young's modulus in such processes is explained. The correspondence between theoretical and experimental data is demonstrated for the example of resonant acoustic vibrations of rods made of aluminum alloy D16.

The joint recurrence analysis is used to reveal differences in the phase synchronization between intermittent photic stimulation and brain responses of patients with cardiac fibrillation of paroxysmal and persistent types. As a measure of phase synchronization between two signals, we consider the mutual correlation factor between recurrence probabilities of corresponding phase trajectories. The value of this coefficient increases upon an increase in the cardiac fibrillation time and in the extent of decline of cognitive functions for brain responses to theta-range frequencies.

In this paper, we demonstrate that the standard theory of thermoelasticity fails in describing stress dependence of laser-exited ultrasound in real dielectric and especially conductive materials. A theoretical model of thermoelasticity considering the thermal perturbation of nonstationary defect states with relaxation is presented and analyzed. To explain the obtained experimental data for metals, it is necessary to also consider a change in the pressure of the electron gas due to the defect perturbation. The proposed model is used to describe linear and nonlinear behavior of the laser ultrasonic signals near a hole in a dielectric ceramic and a metal alloy submitted to a uniform compression. The model introduces an effective dynamic coefficient of thermal expansion for real stressed materials. The obtained results provide an opportunity to estimate mechanical stresses in different materials. In this paper, we describe the calibration of the laser ultrasonic signals on stress in combination with hole drilling. The approach also allows us to estimate relaxation times of the laser-excited defects in stressed materials.

Experimental results on the behavior of laser ultrasonic signals near holes in stressed ceramics and metals are presented. The data obtained are analyzed within the framework of the standard theory of thermoelasticity. It is shown that this approach is not able to explain the behavior of laser ultrasonic signals in stressed materials. A new model of thermoelasticity taking into account thermal perturbation of non-stationary defect states with relaxation is presented and analyzed. It is demonstrated that strong stress dependence of the laser ultrasonic signals provides an opportunity to estimate mechanical stresses in different materials. An example of mechanical stress effect on the laser ultrasonic image near Rockwell indentation zones in metals is presented.

A change in temperature during adiabatic elastic deformation of solids (thermoelastic effect) is determined in terms of the thermodynamic approach taking into account the existence of internal defects in them. A contribution of the defect structure of a material to the Kelvin formula as determined as there are mechanical stresses in a material. It is shown that the changes in the thermal expansion coefficient of a material due to a dependence of the elastic modulus and the defect concentration on temperature can have opposite directionalities.

Based on the analysis of joint recurrences, differences in phase synchronization between rhythmic photostimulation and brain responses were revealed in individuals with atrial fibrillation of paroxysmal and persistent types. As a measure of phase synchronization between two signals, the cross-correlation coefficient between the probabilities of recurrences of the corresponding phase trajectories is considered. With a lengthening of the lifetime of atrial fibrillation and an increase in the degree of decline in cognitive functions, the value of this coefficient increases for brain responses to theta-range frequencies.

The nature of changes in laser photoacoustic signals near small-diameter holes in aluminum and steel layers in a bimetallic plate obtained by hot rolling is investigated. The experimental results are compared with the solution of the classical Kirsch problem for stress distribution around a circular hole in a prestressed material. The possibility of estimating internal stresses by the laser photoacoustic method in combination with the method of drilling holes in industrial bimetallic plates is shown.