Izvestiya of Saratov University.
ISSN 1817-3020 (Print)
ISSN 2542-193X (Online)

Радиофизика, электроника, акустика

Decrease of low-frequency spectral power in a heart rate variability signal in a mathematical model of the cardiovascular system of arterial hypertension patients

Background and Objectives: Index equal to the spectral power of the low-frequency oscillations from the time series of the time intervals between the hearts contractions are often used when investigating the cardiovascular system. Experimental studies have shown that this spectral index was a preclinical marker of cardiovascular diseases, including arterial hypertension and diabetes.

Electrical properties of a composition based on polydimethylsiloxane filled with gallium oxide

In the present paper, the effect of gallium β-oxide introduced into the polydimethylsiloxane elastomer on the electrical properties of the composite material is investigated. The dependence of the electrical resistance of the composition on the change in the specific volume electrical conductivity on the content of gallium oxide is established experimentally and the percolation point is determined. The percolation point is 21%, which is slightly higher than the theoretical value calculated by the Monte Carlo method and is 16%.

Oscillation modes of a linear oscillator, induced by frequency fluctuations in the form of non-Markovian dichotomous noise

Background and Objectives: A set of differential equations is derived for the probability density functions of the phase coordinates of dynamic systems featuring parametric fluctuations in the form of non-Markovian dichotomous noise having arbitrary distribution functions for life at the states ± 1. As an example, the first moment of the phase coordinate of an oscillator was calculated, its perturbed motion being described by a stochastic analogue of the Mathieu–Hill equation.

Уменьшение спектральной плотности интервалов сердечных сокращений в низкочастотном диапазоне у пациентов с артериальной гипертензией в математической модели кровообращения

Оценка спектральной мощности низкочастотных ритмов последовательности интервалов между сердечными сокращениями широко применяется в фундаментальных исследованиях сердечно-сосудистой системы, позволяет выявить маркеры ряда серьезных заболеваний сердечно-сосудистой системы. При этом физиологическая интерпретация этих низкочастотных спектральных составляющих остается предметом дискуссии. Этот вопрос исследовался в ходе математического моделирования динамики сердечно-сосудистой системы здорового человека и пациента с артериальной гипертензией.

Метрология XXI века. Радиотехнические величины и эталоны SI

В статье обсуждается совершенствование методики преподавания курсов теории связи и информации в Саратовском университете путем введения до-полнительных разделов, посвященных метрологии и анализу принципов по-строения систем единиц физических величин, формированию основ Международной системе SI, ее свойств и возможностей. Обсуждается методика расчета новых эталонов радиотехнических единиц измерений на основе современных научно-технических достижений и фундаментальных физических констант.

Experimental study of a bidirectional impulse turbine in a steady gas flow

Background and Objectives: The bidirectional impulse turbine can be used to generate electricity from the energy of sea waves or to convert acoustic energy into electrical energy in thermoacoustic generators. Materials and Methods: In this paper, an experimental study of the characteristics of a bidirectional turbine in a constant gas flow was carried out. The experiments were carried out with a fixed and freely rotating turbine rotor. The outer diameter of the turbine blades is 44 mm.

Influence of noise on generalized synchronization in systems with a complex topology of attractor

Background and Objectives: The goal of the paper is to study the influence of noise on generalized synchronization in unidirectionally coupled systems with a complex topology of attractor. As the systems under study, two models of chaotic systems with two-sheeted topologies of attractors such as Lorenz and Chen systems are considered.


В представленной работе исследовано влияние введенного в полидиметилсилоксановый эластомер β - оксида галлия на электрические свойства композиционного материала. По изменению удельной объемной электрической проводимости от содержания оксида галлия экспериментально установлена зависимость электрического сопротивления композиции и определена точка перколяции. Точка перколяции составила 21%, что несколько выше теоретического значения рассчитанного по методу Монте-Карло и составляющего 16%.

Numerical simulation of stages number influence to the characteristics of a looped tube thermoacoustic Stirling engine

Background and Objectives: The traveling wave thermoacoustic engine is a variation of the Stirling engine family. With an increase in the number of stages of a traveling wave thermoacoustic engine from one to four, an improvement in the characteristics of the acoustic wave in the regenerator zone is observed, the temperature difference between the heat exchangers required to start the engine decreases, and the efficiency increases.

Nonlinear tunneling of electromagnetic wave through a plasma layer

Background and Objectives: The propagation of a strong plane electromagnetic wave from a vacuum through a limited plasma layer is considered, taking into account non-linearity under tunneling and transparency conditions. The temperature dependence is not taken into account. The non-linearity is taken into account phenomenologically as the dependence of the plasma frequency and collision frequency on the field averaged over the period squared.