Vol 24, No 3 (2024)

Background and Objectives: Progress in the development of pulsed radiation sources with high energy density makes it possible to study the nonlinear response of condensed matter to the disturbing influence of high-intensity electromagnetic fields. To understand the processes occurring in this case, adequate models are needed that qualitatively and quantitatively reproduce the characteristics of the materials under study. In this area, graphene is considered one of the most promising materials due to the specificity of its band structure. The purpose of the work is to present and test a new model based on the quantum kinetic equation, free from restrictions on such parameters as the frequency and strength of the electric field of the disturbing influence. Materials and Method: The approach used in the work is based on the quantum kinetic equation for the distribution function of charge carriers in the state space. It makes it possible, in the one-electron approximation, to nonperturbatively reproduce the ultrafast dynamics of carriers in an external classical electric field. The system under consideration is specified by the electron dispersion law. The approach was developed and implemented for the pseudo-relativistic approximation of massless fermions, successfully used in describing the features of graphene. However, by its definition, this approximation quite accurately reproduces the real dispersion law only in the low-energy region in the vicinity of the Dirac points. Therefore, the direct use of this version of the model to describe processes in which electronic states with high excitation energies are known to participate raises questions about the accuracy of the results obtained. The problem can be resolved by moving to an exact definition of the dispersion law through the parameters of the tight-binding model of nearest neighbors in the crystal lattice of the graphene. The presented work proposes an implementation option for such a procedure and verifies the results obtained. A generalization of the formalism for a two-level system with a massless Hamiltonian of general form is used, which universally defines the explicit form of the quantum kinetic equation and expressions for macroscopic observable parameters. Results: A computational model based on the exact tight-binding model Hamiltonian has been determined, which strictly takes into account the real law of graphene dispersion in reciprocal space. The new model has been verified. For this purpose, the results of its use are compared with the results of a similar model based on the massless fermion approximation. Under conditions of limiting the parameters of the perturbing influence, ensuring the generation of excited states with only low energies in the immediate vicinity of the Dirac points, an exact coincidence has been demonstrated both at the stage of determining the values of the distribution function and for the observed parameters. It has been shown that going beyond the applicability limits of the massless fermion approximation is accompanied by the appearance of qualitative and quantitative differences in the results obtained. Conclusion: The results of the work provide new opportunities for studying the behavior of graphene under extreme conditions of strong high-frequency fields, modeling and searching for new nonlinear effects, and accurately reproducing the ultrafast quantum dynamics of its electrons for states with high energy values.

Background and Objectives: The purpose of the research is to establish whether it is possible to determine the degree of anaesthesia that a laboratory animal is experiencing noninvasively. For this objective the usage of such methods of electroencephalogram (EEG) signal analysis as fast Fourier transform, K-Means machine learning method and statistical analysis is discussed. Models and Methods: The EEG data was obtained through an experiment where two groups of laboratory rats received different types of anaesthetic agent. The EEG data was normalised,then the power spectra were computed using fast Fouriertransform. Next, the K-Means method was applied to classify the data in accordance with the anaesthesia degree. Statistical analysis was also conducted to describe prominent characteristics of each stage. Results: It has been shown that the proposed data analysis methods allow to distinguish between normal state, anaesthesia, and death with increasing anaesthesia dosages in laboratory animals.

Background and Objectives: The search of new effective antibacterial drugs and the development of more advanced dosage and delivery systems for existing antibiotics (AB) are actual research objectives for biomedical science. During the study emulsion microgels (EM), based on whey protein isolate, containing antibacterial drugs (cefazolin (CZ), ceftriaxone (CT)) were obtained by ultrasonic homogenization method. The effect of AB-loaded EM on E. coli strain was studied in comparison to free AB. Materials and Methods: The formation of oil-in-water microemulsions stabilized by whey protein isolate (WPI) in saline was carried out using the method of spontaneous emulsification during ultrasonic homogenization using a rod ultrasonic homogenizer. This approach is based on the denaturation of protein under ultrasonic influence on a solution of biomolecules with the subsequent formation of a microgel shell on the surface of oil droplets. Quantitative characteristics of antibiotics loading and its release from microgels were determined spectrophotometrically. Visualization and calculation of EMs particle sizes were carried out using an optical microscope. The study of AB-loaded EM antibacterial action was performed in liquid nutrient media followed by seeding onto nutrient agar. The experiment was followed with live-dead test, carried out by flow cytometry with cell visualization. Results: The rate and characteristics of AB release from the obtained carriers in various model media, as well as the antimicrobial activity of microgels, have been studied. It has been found that the release of AB from synthesized carriers on the first day of the experiment is 10% in all studied model systems. The total amount of AB released over 144 hours reaches 20% in saline solution and 30% in artificial urine. According to the results of the experiment, all samples of EM, containing CZ caused inhibition of E. coli growth within 7 days. Of these, total suppression of bacterial growth was observed within 1 day for EM 1 : 3 and 1 days for EM 1 : 5, on the remaining days – partial growth suppression. Free CZ remained active during the first day. EM, containing CT, demonstrated an antibacterial effect for 14 days. In this case, the bactericidal nature of the action was observed within 10 days for EM 1 : 3 and 13 days for EM 1 : 5. Free CT also had an antimicrobial effect for 14 days, but the duration of the period of complete growth inhibition in all control samples was significantly shorter compared to EM samples. Conclusion: The immobilization of antibacterial drugs (CZ, CT) into emulsion microgels not only does not lead to a decrease in their effectiveness, but also makes it possible to significantly increase the duration and intensity of action of these drugs. The results obtained are of interest for further study of the possibilities of using emulsion MGs based on WMB as carriers of antibacterial drugs.

Background and Objectives: According to known experimental data, various metabolites of arachidonic acid have a vasoconstrictor or vasodilator effect, which in turn affects neuronal activity. The level of metabolite production can be influenced in several ways: by regulating oxygen levels or by glutamate-dependent increases in astrocytic calcium concentrations in response to neuronal activity. To analyze possible patterns of activity of nervous tissue in response to changes in the metabolic profile, a mathematical model was developed, within the framework of which computational experiments were carried out both in the local case and on spatial patterns. Materials and Methods: The work proposes a point model and its further extension for a spatially distributed system of connected neurogliovascular units. To test the performance of the model, we include an external influence leading to an increase in neuronal potassium and the occurrence of cortical depression, and an external influence on calcium activity, in order to analyze the influence of arachidonic acid metabolites on the process under study. Results: A new point model of the neurogliovascular unit has been developed that simulates the effect of arachidonic acid metabolites on cortical spreading depression, while expanding the point model to a spatially distributed case allowed us to determine the ways in which astrocytic activity influences the spatiotemporal characteristics of the wave of cortically spreading depression. Numerical studies of point and spatial models have confirmed the correspondence of the solutions to the observed experimental effects, including those associated with the peculiarities of the influence of arachidonic acid metabolites on the speed, area and lifetime of depression waves. It is assumed that in the future the results of the theoretical study can be used to find ways to return nervous tissue to the normal state from pathological conditions that occur with epilepsy, migraines and other neurodegenerative conditions associated with the occurrence of cortical depression waves. 

Background and Objectives: Nanostructured dispersed semiconductor structures are of some interest as functional materials for modern chemoresistive sensing and photocatalytic chemistry. Among the promising semiconductor materials for such applications is, in particular, titanium dioxide in the modification of anatase. Despite a significant number of experimental and theoretical works devoted to the consideration of electrophysical properties of anatase nanophase and various structures based on it, the features of degradation of electrical conductivity of such systems with time are not fully investigated. The aim of this work was to analyze the behavior of the fluctuation component of the voltage drop on partially conducting systems of interelectrode bridges made of anatase nanoparticles under conditions of direct current flow in the quasi-stationary regime (with a slow increase in the voltage drop) and as it approaches the threshold of flow, characterized by a rapid increase in the voltage drop. Materials and Methods: Experimental studies of the charge transfer fluctuations in disperse structures near the percolation threshold were carried out using specially prepared samples consisting of densely packed titanium oxide nanoparticles (TiO2). The technique is based on the registration of time dependences of the voltage drop across the structures when a constant current flows through the system of anatase bridges. The behavior of fluctuation components during the measurement cycles was analyzed using moving estimates of the Hurst exponent of sample structural functions of intensity fluctuations. In addition to the sample values of the Hurst exponent, the sample normalized autocorrelation functions of the fluctuation component were calculated. To interpret the observed features, we propose a qualitative phenomenologicalmodel that considers the influence of random sequences of acts of blocking and soft breakdown of local conduction channels in the studied structures on the degradation of the effective ohmic conductivity of the structures. Results: It has been established that when approaching the threshold of percolation due to the depletion of the ensemble of free charge carriers (electrons) in bridges, there are qualitative changes in the dynamics of voltage drop fluctuations on bridge systems (in particular, a significant increase in the Hurst exponent of structural functions of voltage drop fluctuations, correlating with a sharp decline in the effective ohmic conductivity of the structures under study). “Soft” breakdowns of previously blocked local conduction channels may be due to the Poole – Frenkel effect, leading to the escape of trapped electrons into the conduction zone due to thermal fluctuations when the depth of traps decreases under the influence of an external electric field. Conclusion: The results obtained are of some interest from the point of view of further development of fundamental ideas about charge transfer mechanisms in dispersed semiconductor materials used in chemoresistive sensing and catalytic chemistry.

Background and Objectives: Using sol-geltechnology, silicate mesoporous single layer coatings based on SiO2@CuO(ZnO) compositions were obtained to increase glass transparency. The phase composition and properties of powders obtained from dried sols were studied. The optical properties of the obtained silicon oxide sols were explored by the turbidimetric method. To identify the characteristics of gelation and coagulation, a spectrophotometric study of the silicon oxide sol was carried out. The resulting sols were applied to glass by adsorption from solution (dip-coating) at room temperature (23 ± 10°C). The rate of extraction from the solution varied from 105 to 160 mm/min. Glasses with coatings applied to both sides were dried at room temperature until a film formed and subjected to heat treatment in a muffle furnace at a temperature of 500°C. At the moment of annealing, the decomposition of copper and zinc salts and the formation of a composite composition of SiO2@CuO and SiO2@ZnO films occurred. Spectral measurements of the transmittance and reflection of glasses with single layer mesoporous coatings were carried out in the range of 400–800 nm. Materials and Methods: To obtain sols with copper and zinc, metal salts Zn(CH3CO2)2 ·2H2O and (CH3COO)2Cu·H2O (6% or 10% by weight SiO2) were added to the SiO2 sol. Using a magnetic stirrer, the resulting mixtures were stirred at room temperature for 15 ± 0.5 min. To study the optical properties of the sols, a base SiO2 sol and SiO2 sols with the addition of zinc acetate and copper acetate (6% and 10% by weight of silicon dioxide) were prepared. After heat treatment, the thickness of the applied coatings was determined by contact method using a Dektac-150 profilometer. It was determined that the thickness of the coatings on glass varied from(95 ± 20) to (137 ± 7) nm at drawing speeds of 105 and 160 mm/min, respectively. Results: The developed methods for producing mesoporous silicate coatings on glass have ensured the creation of homogeneous coatings with good adhesion, uniform thickness and roughness. The results of measuring the transparency spectra of glass with a single layer coating of sols with different compositions and drawing rates have been presented. It has been shown that double-sided single-layer mesoporous SiO2@CuO(ZnO) composite coatings with different compositions demonstrate an increase in glass transparency by 2-3% in a wide optical range of 400–1000 nm. Conclusion: The proposed composition of compositions in single layer film structures makes it possible to solve the problem of broadband antireflection of glasses in a wide range of optical wavelengths (400–1000 nm). 

Background and Objectives: Silicon is the main semiconductor material used in many areas of human life. It is used in the creation of solar cells, various electronic devices, sensors etc. Also of particular interest is such an actively developing area as flexible electronics. It finds its application in the electronic devices. Thus, it becomes important to study ways to create polycrystalline films of semiconductor materials such as silicon on flexible substrates. The biggest problem with silicon crystallization on flexible substrates is that these substrates are low-melting, and traditional methods of silicon crystallization have an intense thermal effect on the crystallized material, which leads to destruction of the substrate. Materials and Methods: To create the samples, consecutive magnetron sputtering deposition of a silicon layer and then a tin layer onto a polyimide substrate was used. Silicon was crystallized using an infrared pulsed laser due to high absorption in tin layer. The structure of silicon during its bending deformation was studied using Raman spectroscopy. Results: As a result of the study, the sizes of silicon crystallites after crystallization, as well as the stresses in the films during bending, have been determined.

Background and Objectives: In the history of physics and mathematics education at Saratov State University in the 1920s–1950s,the personality of Georgy P. Boev (November 25, 1898 – July 8, 1959) occupies a prominent place. He was one of the first students and graduates of the Faculty of Physics and Mathematics opened at the university in 1917, its first graduate student, the first dean of the Faculty of Mechanics and Mathematics, and the first scientific director of the computer center of Saratov State University. The article describes the various stages of the creative biography of Georgy P. Boev: the period of study and work as a lecturer at Saratov State University in 1917–1930, the period of work as a professor and head of the department of mathematics at the Ivanovo Textile Institute (1930–1934), the second period of work at Saratov State University as a professor and head of mathematics departments (1934–1959), as well as acting director of the Research Institute of Mathematics, Mechanics and Physics at Saratov State University (1939–1941), dean of the Faculty of Physics and Mathematics (1943–1945), dean of the Faculty of Mechanics and Mathematics (1945–1947), Vice-Rector of Saratov State University for Academic Affairs (1947–1950), scientific director of the problem laboratory “Computing Center” (1957–1959). Materials and Methods: The presentation of the biography of Georgy P. Boev is based on archival materials, his personal notes and memories of colleagues, and an analysis of his scientific heritage. Conclusion: The article pays tribute to the extraordinary personality of Georgy P. Boev and at the same time serves as an illustration of the historical conditions that developed in the field of higher education in the country in which he was destined to live and work.