Vol 24, No 2 (2024)

Background and Objectives: In practice, there are often processes in which in the initial state the working medium is single-phase, for example, in the form of gas (steam), and during the process under study conditions are created for the appearance of a new phase in the form of droplets (nuclei). The process of nucleation and further condensation growth of clusters in supersaturated vapor is one of the most important processes leading to the development of the dispersed phase. The liquid phase nuclei that appear as a result of nucleation are quite small (nano-sized) and, therefore, subject to Brownian wander, which leads to their mutual collisions and coagulation. The processes of evaporation and condensation in various media are used to obtain nanomaterials (in particular, in the synthesis of carbon nanotubes), as well as to obtain nano- and ultradisperse particles in expanding channels due to nucleation and their condensation and coagulation growth. Materials and Methods: Using a quasi-equilibrium model based on the equations of mechanics of multiphase media, the flow of a dispersed mixture in a channel with sudden expansion in the presence of processes of nucleation, coagulation of nuclei (clusters) and phase transitions (evaporation, condensation) in a two-dimensional formulation was studied. The homogeneous nucleation model is used to describe the nucleation process. It is assumed that the process of coagulation of clusters occurs due to their Brownian motion. To determine the rate of phase transitions, the Hertz – Knudsen – Langmuir formula is used. The problem of the flow of a gas-dispersed mixture in a channel with sudden expansion in a twodimensional formulation is considered. It was assumed that in the narrow part of the channel, under certain conditions, nuclei of the dispersed phase continuously appear, which enterthewidened part ofthe channelwiththe flow. The calculationswere carried out based onthe algorithm of the numerical “large particles” method, which is based on splitting the original equations into physical processes. Results: As a result of the study, the basic properties of the flow of a two-phase mixture in a channel in the presence of nucleation, coagulation and phase transitions have been established. It has been shown that the flow has a vortex structure, and the largest particles are formed precisely in the vortex zone. Calculations have established that the coagulation process has a fairly strong effect on the distribution of cluster sizes inside the channel. The influence of the degree of steam supercooling on the flow of the dispersed mixture in the channel has been studied and it has been found that this parameter significantly affects the density distribution of the dispersed phase. The flow pattern obtained using calculations is consistent with experiment. Conclusion: The basic properties of the behavior of the mixture parameters along the expanding channel at presence of nucleation, coagulation and phase transitions have been established. The results obtained can be useful in various areas of modern technology: when designing various heat-power and heat-exchange installations, for studying the process of outflow of various mixtures from containers, for modeling the processes of formation and growth of nuclei (in particular, nanoclusters) in saturated media, etc.

Background and Objectives: Graphene and its derivatives are promising materials for the fabrication of biosensors with high sensitivity and low detection limits due to their large specific surface area, excellent flexibility and strength, and high electrical conductivity. This work examines holey graphene, which has been successfully synthesized and has already found its application in nano- and bioelectronics. It is known from experimental data that the free edges of holes in the structure of holey graphene contain functional groups, the influence of which should be taken into account when developing sensor devices based on it. The purpose of this work was to establish the patterns of the influence of functionalization with carbonyl and carboxyl groups on the electronic energy parameters of holey graphene. Materials and Methods: The object of study was a film of holey graphene with almost circular holes with a diameter of 1.2 nm. All calculations were performed using the self-consistent-charge density functional based tight binding method in the DFTB+ software package at a temperature of 300 K. The process of functionalization of holey graphene was modeled using an original algorithm for step-by-step placement of functional groups on atoms at the edges of the hole. Results: Based on the calculation results, we have revealed the patterns of redistribution of the electron charge density between functional groups and holey graphene and the features of changes in the Fermi level of a graphene object during functionalization. Conclusion: The revealed patterns are important in the development of sensitive elements of sensor devices made on the basis of holey graphene.

Background and Objectives: Manifestations of intermolecular interaction based on hydrogen bonding in hyaluronic acid IR spectra and in multicomponent mixtures of hyaluronic acid with nitrogen-containing amino acids, which are part of mucin of the mucous membrane of the bladder and protein carrier microgels, have been studied using experimental and theoretical IR spectroscopy. Materials and Methods: Comparison of measured and calculated hyaluronic acid IR spectra in harmonic approximation is performed. Calculations of molecular complexes structure and their corresponding IR spectra were carried out, followed by an analysis of the parameters of the hydrogen bonds formed. Results: Estimates of hyaluronic acid complexation with amino acids strength, which are part of protein microgels used in targeted therapy, and in target cells proteins were given. Conclusion: It has been found that the presence of an additional protein structure significantly increases the hyaluronic acid interaction with mucous membrane mucin protein due to intermolecular complexation based on polar basic amino acids.

Background and Objectives: The purpose of this work is to study the influence of the extracellular matrix of the brain on the formation of burst dynamics of a spiking neural network. Materials and Methods: The Izhikevich neuron model was used as a neuron model. To describe the dynamics of the extracellular matrix of the brain, the phenomenological model of Kazantsev, constructed using the formalism of the Hodgkin – Huxley model, was used. A model of the formation of burst dynamics of a spiking neural network under the influence of the extracellular matrix of the brain was developed and studied. Results: The main dynamic modes of neural activity have been obtained in the absence of regulation and in the presence of the extracellular matrix of the brain. Conclusion: It has been explored how the modulation by the extracellular matrix of the brain can influence the frequency of burst activity of the neural network. It has been found that the regulation of neural activity, mediated by the extracellular matrix of the brain, promotes the grouping of spikes into quasi-synchronous population discharges, called population bursts. In this case, an increase in the strength of the influence of the extracellular matrix of the brain on postsynaptic currents through synaptic scaling leads to an increase in the degree of synchrony of neuron populations.

Background and Objectives. There is a global trend towards an increase in the number of patients diagnosed with ovarian cancer during their reproductive years. One of the current clinical technologies is the technology of cryopreservation of removed healthy ovaries in order to preserve fertility and their subsequent transplantation after treatment for cancer of other organs. Glycerol is often used as a non-penetrating agent in freezing to improve follicle survival. Materials and Methods. The work examined the ovaries of cats with diagnoses confirmed by histological studies: follicular phase, luteal phase, serous carcinoma, leimyosarcoma. Diffuse reflectance spectroscopy was used to determine the kinetic parameters of dehydration and optical properties of tissues upon interaction with glycerol. Based on the change in mass over a long period of time, the diffusion coefficient of glycerol in the samples was determined. Results. The effective diffusion coefficient of interstitial water in cat ovarian tissue has been measured: D = (2.6 ± 0.4)·10−6 cm2/s (follicular phase), D = (3.3 ± 0.4)·10−6 cm2/s (luteal phase), D = (3.0 ± 0.3)·10−6 cm2/s (leiomyosarcoma), and D = (1.6 ± 0.2)·10−6 cm2/s (serous carcinoma), which is initiated within 1.5–2 hours of interaction. Diffusion of glycerol occurs over a long period of time, about 400 hours, and for the samples under study is: D = (8.3 ± 2.5)·10−8 cm2/s (follicular phase), D = (5.6 ± 1.7)·10−8 cm2/s (luteal phase), D = (2.2 ± 0.2)·10−8 cm2/s (leiomyosarcoma), and D = (1.1 ± 0.4)·10−7 cm2/s (serous carcinoma). Conclusion. The established perfusion-kinetic parameters of glycerol/interstitial water for the studied samples can be used in clinical practice in the preparation of ovarian tissue for transplantation (cryopreservation), in the transmembrane transfer of drugs, the development of new reproductive technologies, etc.

Background and Objectives: Magnetic fluids are unique nanodispersed systems that have the properties of a magnetic material and a liquid. Although their magnetic properties are inferior to steels and ferrites, they are supermagnetic compared to most liquid media. When a magnetic field is applied to a magnetic fluid, agglomerates of ferromagnetic nanoparticles are formed in it, which were visually observed in this work. Materials and Methods: The dependence of the modulation depth of laser radiation with wavelengths of 450 nm, 550 nm and 650 nm on the concentration of nanotubes and the magnitude of the magnetic field induction is studied. The transmittance of polarized radiation in the optical range is measured depending on the relative position of agglomerates of ferromagnetic nanoparticles and the vector of the electric field strength of laser radiation. The angle between the electrical component of the laser radiation and the magnetic field induction vector changes by rotating the laser diode and polarizer with a servomotor relative to the vertical axis. Results: The maximum value of the modulation depth for magnetic fluid without carbon nanotubes is 15% and is observed for laser radiation with a wavelength of 650 nm. Adding multi-walled carbon nanotubes to the magnetic fluid makes it possible to increase the modulation depth by approximately one and a halftimes. Conclusion: It has been revealed that with increasing wavelength of laser radiation, the modulation depth increases. As the magnetic field induction value increases, the modulation depth of polarized laser radiation increases for all wavelengths. The addition of carbon nanotubes to the magnetic fluid leads to their alignment along the agglomerates.

Background and Objectives: The article systematizes biographical information about Sergey A. Boguslavsky, an outstanding Russian theoretical physicist of the first quarter of the 20th century, one of the first professors of the Faculty of Physics and Mathematics of Saratov University (1918–1921). In 1911–1922, he carried out important theoretical works in the field of crystal physics, pyroelectricity, thermodynamics, hydrodynamics and vacuum electronics. Boguslavsky’s life was complicated by some serious illness. Materials and Methods: By writing this article, the scientific works by Sergey A. Boguslavsky, the memoirs of his contemporaries – employees of Göttingen, Moscow and Saratov universities, datafromthe archive of Saratov State Universitywere used. Conclusion: The significance of scientific works by Sergey A. Boguslavsky for physics of his time and their interest in the context of history of physics, methodology of representing fundamental and practical results of scientific creativity, organizing higher education in complex public and personal circumstances, and preservation of historical memory are noted. The article is the most complete biography of Sergey A. Boguslavsky.