bluuebunny/crossref_metadata_2025 huggingface dataset:
Large-Scale Disturbances of the Solar Wind According to Spacecraft
Radio Transmission Data from the Mars Express and Local
Measurements on the Wind Spacecraft
Authors: Efimov A. I. , Smirnov V. M. , Chashei I. V. , Nabatov A. S.
Published: April 2024

The results of experiments on radio sounding of near the Sun plasma by the signals of the MarsExpress Mars satellite are presented. In the region of heliocentric distances of the proximate point of the lineof sight of 8–13 solar radii, frequency fluctuations of transmission radio signals were measured. During theexperiments sharp increases in the variance of frequency fluctuations were recorded on both the eastern andwestern limbs. In measurements near the Earth’s orbit on the Wind spacecraft in adjacent periods with a delayof 5–17 days, increases in the proton concentration and magnetic field strength were recorded at 7–15 times thebackground values. A comparison between the data related to the inner and near-Earth solar wind indicates thatthe observed disturbances are associated with the same region of the solar corona rotating with the Sun
Features of Forecasting the Operation of Ionospheric Radio Lines
in Upper Rays Modes
Authors: Krasheninnikov I. V. , Shubin V. N.
Published: April 2024

The frequency dependence of transmitted information qualitative indicators is analyzed on theexample of two meridional radio links: single-hop (~2600 km) and dominant two-hop (~5100 km) for basicmodes of radio wave propagation in the ionosphere. It is shown that the presence of highly efficient receivingtransmittingantennas in a radio communication system leads to the need to take the existence of a priori energeticallyextremely weak modes into account in the problem of radio path specification statement. In thiscase, we consider those formed exclusively by the mechanism of radiation transfer along the upper-angles raytrajectories in the ionospheric propagation of radio waves. If the angles of departure and arrival for suchmodes and the directions of the main lobes of the antenna patterns at the end points of the radio path coincide,the signal-to-noise ratio for the wave field can reach the required threshold value and ensure the successfuloperation of the radio communication system. This may expand the upper frequency limit for the passageof radio waves in the transition regions of jump propagation of radio waves in the ionosphere; it shouldbe taken into account in forecasting the operation of ionospheric radio links.
Multiyear Trends of the Ion Composition and Temperature of the Mid-Latitude Lower Thermosphere
Authors: Givishvili G. V. , Leshchenko L. N.
Published: April 2024

Experimental data on measurements of the nitric oxide NO content in the mid-latitude lower thermosphere demonstrate its significant dependence on solar (and correspondingly) geomagnetic activity, which varies from undisturbed to strongly disturbed conditions up to three or four times or more. Such a dependence of [NO] on heliogeophysical factors cannot but affect the content of NO+ ions, which predominate (together with O+2 ions) at heights of 105–120 km. The analysis in the present work has confirmed this assumption: the φ+ = [NO+]/[O+2] ratio in the mid-latitude E layer of the ionosphere is indeed intricately correlated with solar activity. At the same time, data from vertical sounding of the ionosphere for 86 years of observations indicates a systematic multiyear increase of the critical frequency of the E layer (foE) at a fixed level of solar activity. Taking into account these circumstances made it possible to estimate the long-term variations of the neutral atmosphere temperature near the peak height of the E layer (hmE = 110–115 km). The calculations showed that between1931 and 2017, the annual mean temperature of the mid-latitude lower thermosphere increased at a linear rate exceeding 0.3–0.5 K/yr.
Rapid Gas-Chromatographic Determination of Phenol and Cresols in Water by Extractive Freezing-Out
Authors: Bekhterev V. N.
Published: April 2024

A rapid procedure for the determination of phenol and cresol isomers in drinking, sea, and polluted domestic wastewater is developed based on a single-stage extraction of analytes by extractive freezing-out under sample centrifugation conditions. In combination with gas chromatography, the procedure provides the minimum detection limits for each of phenols in 10 mL of water at a level of 0.0005 µg/mL. The duration of sample preparation does not exceed 30 min; the consumption of the ethoxyethane extractant is 1.4 mL. In comparison with liquid–liquid and solid-phase extraction traditionally used at the stage of sample preparation, the proposed procedure is simpler and more environmentally friendly. The stages of filtering samples and dehydrating extracts are excluded; the amount of chemical glassware is minimized.
Linear Correlations of the Gas Chromatographic Retention Indices of Compounds from Various Taxonomic Groups
Authors: Zenkevich I. G.
Published: April 2024

Despite the constant improvement of complex computer algorithms for the calculation of gas chromatographic retention indices (RIs), the simplest methods for their evaluation based on linear correlations between the indices of structural analogs from different taxonomic groups, RI1 ≈ aRI2 + b, remain important. It is shown that symbatic variations of the first numerical differences of retention indices,= RIn + 1 – RIn (equivalent to the first derivatives of the retention indices with respect to the structural parameter varied in the group), are the conditions of correctness for such correlations in the simplest groups (substituted methanes). A monotonic variation ofin one of the groups with the presence of extrema in the other group is an unequivocal sign of the absence of a linear correlation between retention indices. If the values ofin one of the groups increase and decrease in the other, the ranking order of compounds in any one of them should be reversed. It is shown that the simplest relationship RI1 ≈ aRI2 + b is also applicable to more complex taxonomic groups (substituted ethanes, benzenes, and naphthalenes), and it allows one not only to estimate the RIs of compounds not yet characterized but also to refine known reference data.
Preparation of NASICON Na3Zr2Si2PO12 by Pyrolysis of Organic Solutions: Features of Phase Formation
Authors: Grishchenko D. N. , Kuryavyi V. G. , Podgorbunsky A. B. , Medkov M. A.
Published: April 2024

A new promising method for the synthesis of NASICON (Na3Zr2Si2PO12) by pyrolysis of organic solutions has been developed. Sodium oleate, zirconyl oleate, tributyl phosphate, and tetraethoxysilane have been used as precursors. The molar ratios of the components of the mixture for the formation of NASICON have been established. The effect of sodium on the formation of the zirconium dioxide phase has been proven. A finely dispersed material with an average grain size of 0.2 µm has been obtained. Changes in morphology and composition depending on the time and temperature of firing the sample are studied. The results have been confirmed by X-ray powder diffraction and scanning electron microscopy. To refine the parameters of the crystal lattice, a full-profile analysis has been performed by the Rietveld method. The process of obtaining NASICON takes about 9 h, i.e. it is the least time consuming of all the alternative ways of synthesis. The advantages of this method are the possibility of lowering the sintering temperature, the absence of the need to control many parameters during synthesis, and minimizing the duration and multi-stage process. The method contributes to the development and production of more promising ion-substituted structures.
Synthesis, Thermodynamic Properties, and Ionic Conductivity of Compounds Based on Bismuth Niobates Doped by Rare-Earth Elements (A Review)
Authors: Matskevich N. I. , Semerikova A. N. , Samoshkin D. A. , Stankus S. V. , Zaitsev V. P. , Kuznetsov V. A. , Novikov A. Yu.
Published: April 2024

Synthesis methods, thermodynamic and functional properties of compounds based on bismuth niobates doped with rare-earth elements (REEs) are presented. These compounds are promising materials for fuel cells, ceramic oxygen generators, electrocatalysis, etc. As show the data generalized, most compounds have a cubic structure of the δ-form of bismuth oxide, which has the highest ionic conductivity among solid-state ionic conductors. The compounds have high lattice enthalpy and are therefore promising high-energy compounds. The review summarizes studies on the basic thermodynamic characteristics of bismuth niobates doped with rare earth elements. The change in standard enthalpies of formation, lattice enthalpies, and heat capacity when replacing one rare earth element with another is analyzed. It is shown that as the radius of rare earth elements decreases, the standard enthalpies of formation increases and lattice enthalpies increases. The change in ionic conductivity with changes in temperature and rare earth element content has been studied. It has been shown that with increasing temperature and REE content, conductivity increases.
Intraspecific typing and phylogeny of the causative agent of the plague – the microbe Yersinia pestis: Problems and perspectives
Authors: Suntsov V. V.
Published: April 2024

Two approaches to typing (analysis of intraspecific diversity) and reconstruction of the phylogeny (evolutionary history) of the causative agent of the plague – the microbe Yersinia pestis – molecular genetic (MG) and ecological (adaptationist, on the basis of host adaptation) are considered. It is shown that each of the approaches has its advantages and disadvantages. MG-typing of pathogen strains in the studied foci of the world made it possible to characterize up to 30 subspecies/genovariants of the plague microbe, but the phylogeny of the microbe built on the basis of this diversity contradicts some obvious environmental facts. The ecological scenario of the origin and evolution of the causative agent of the plague has no obvious contradictions and, as an evolutionarily based hypothesis, it should be taken into account in MG reconstructions of the phylogeny of the plague microbe. The prospect of research in this direction is seen in integrating molecular-genetic (statistical) and ecological (adaptationist) approaches.
Synthesis and antibacterial activity of 4-oxo-2-thienylaminobut-2-enoic acids
Authors: Gorbunova I. A , Shadrin V. M , Pulina N. A , Novikova V. V , Dubrovina S. S , Shipilovskikh D. A , Shipilovskikh S. A
Published: April 2024

The hydrolysis of substituted 3-(3-cyanothiophen-2-yl)imino-3 H -furan-2-ones was studied. It was found that the reaction proceeds with the opening of the furan ring and the formation of the corresponding 4-oxo-2-(3-cyanothiophen-2-yl)aminobut-2-enoic acids. The antibacterial activity of the obtained compounds against Staph ylococcus aureus , Escherichia coli and Candida albicans was studied.
Synthesis and structure of 4-aryl-3,6-dioxo-2,3,4,5,6,7-hexahydroisothiazolo[5,4-b]pyridine-5-carbonitriles
Authors: Dotsenko V. V , Jassim N. T , Temerdashev A. Z , Aksenov N. A , Aksenova I. V
Published: April 2024

Oxidation of triethylammonium 6-amino-4-aryl-3-carbamoyl-5-cyano-1,4-dihydropyridine-2-thiolates with DMSO-HCl system leads to the formation of novel 4-aryl-3,6-dioxo-2,3,4,5,6,7-hexahydroisothiazolo[5,4- b ]pyridine-5-carbonitiriles. Structure of the obtained compounds was studied using two-dimensional NMR spectroscopy and HRMS methods. An in silico predictive analysis was carried out to identify bioavailability parameters and possible protein targets for the obtained compounds.
Photochemical production of molecular hydrogen in the presence of substituted acridine salts
Authors: Dolganov A. V , Klimaeva L. A , Okina E. V , Knyazev A. V
Published: April 2024

The photocatalytic properties of new representatives of the family of metal-free catalysts, 10-hydro-9-phenylacridine, 10-methyl-9-phenylacridinium chloride, and 10-phenyl-9-phenylacridinium chloride, were studied with respect to the reaction of molecular hydrogen generation in the presence of acids of different strength (HClO4, CH3SO3H, and CF3COOH) and reducing agents ([Bu4N]Cl, [Bu4N]Br, and [Bu4N]I). It was found that the strength of acids (p K a) and the nature of the reducing agent ( E 0) significantly affect the efficiency, i.e. turnover frequency (TOF), of the process under study. The amount of formed molecular hydrogen reaches its maximum in the case of the combination HClO4 and [Bu4N]I, characterized by minimal p K a and E0 values, respectively. The influence of the nature of substituents at the nitrogen atom in 9-phenylacridine on the efficiency of the molecular hydrogen production was analyzed. It was shown that the limiting stage of the process is the protonation of the formed radical.
Synthesis, spectral-luminescent and ionochromic properties of rhodamine B containing terminal (4-hydroxybenzyl)triphenylphosphonium chloride substituent
Authors: Popov L. D , Shepelenko E. N , Podshibyakin V. A , Valova T. M , Venidiktova O. V , Ayt A. O , Dubonosov A. D
Published: April 2024

A rhodamine B derivative containing a terminal (4-hydroxybenzyl)triphenylphosphonium chloride substituent was synthesized. Its structure was determined using IR, 1H NMR and 13C spectroscopy. The spectral luminescent properties and complexation of the compound obtained in solutions with Co2+, Cu2+, Ni2+ and Zn2+ cations were studied. These ions cause a contrasting ionochromic naked-eye effect with the change of colorless solution to crimson-red color due to the isomerization of the spirolactam form of rhodamine into an open form. The process is accompanied by the appearance of fluorescence in the region of 560-600 nm. The complex with zinc(II) cation exhibits particularly intensive emission, which gives the obtained rhodamine the properties of a highly sensitive and effective chemosensor for Zn2+ ions.
Composite films based on polyacrylonitrile and detonation nanodiamonds
Authors: Soboleva O. A , Porodenko E. V
Published: April 2024

The properties of composite films based on polyacrylonitrile and detonation nanodiamonds were studied. It was established that the surface properties of the films (roughness and free surface energy) do not change when nanodiamonds are added. It was shown by autoradiography technique with tritium-labeled nanodiamonds that the distribution of particles in a film depends on the modification of their surface. Additives of particles and heat treatment affect the mechanical behaviour of the films, the samples become more brittle. Modification of the nanodiamonds with perfluorononanoic acid leads to a decrease in the strength of the films.
Reactions of triethyl phosphonoacetate, bromoacetaldehyde diethyl acetal, and (diethoxyphosphoryl)acetaldehyde with thiourea and (thio)semicarbazide
Authors: Allahverdiyeva G. E , Ismailov V. M , Mamedov I. A , Yusubov N. N
Published: April 2024

Condensation of thiocarbamide with triethyl phosphonoacetate leads to S -phosphorylated 2-ethoxy-4-oxo3,4,5-trihydro-1,5,2-diazaphosphinine-2-oxide, an isostere of thiobarbiturate. Under similar conditions, triethyl phosphonoacetate reacts with semicarbazide with the intermediate formation of 2-(diethoxyphosphorylacetyl) hydrazine-1-carboxamide, which forms a triazine upon cleavage of the P-C bond and 1,2,3-phosphadiazole upon cleavage of the C-N bond. Under analogous conditions, the condensation of triethyl phosphonoacetate with thiosemicarbazide proceeds with cleavage of the Р-С bond and heterocyclization with the formation of the 1,3,4-thiadiazine derivative. Upon condensation of bromoacetaldehyde diethyl acetal with thiosemicarbazide, 4 H -1,3,4-thiadiazine-2-amine was formed. (Diethoxyphosphoryl)acetaldehyde reacts with thiosemicarbazide under the same conditions in a ratio of 1:2, forming a linear product, thiophosphatoiminohydrazone of (diethoxyphosphoryl)acetaldehyde.
Reusable Pd-polymetallic catalysts based on magnetic ferrites for Suzuki reaction in ionic liquid
Authors: Bumagin N. A
Published: April 2024

Based on magnetic ferrites of iron (magnetite), cobalt and nickel modified with 3-aminopropyltriethoxysilane (APTES) hybrid materials Pd-Fe-Co-Ni/MFe2O4@Si-NH2@Pd (M = Fe, Co, Ni) with a protective palladium coating were synthesized. Due to the synergistic effect, new Pd-polymetallic composites exhibit high catalytic activity in the Suzuki reaction in an aqueous solution of an ionic liquid. The developed catalysts are easily removed from the reaction mixture by magnetic decantation and can be reused several times without loss of catalytic activity.
Synthesis of new imidazolidin-2-ones based on the reaction of 1-(2,2-dimethoxyethyl)urea with C-nucleophiles
Authors: Smolobochkin A. V , Kuznetsova E. A , Gazizov A. S , Burilov A. R , Pudovik M. A
Published: April 2024

The acid-catalyzed reaction of 1-(2,2-dimethoxyethyl)ureas with aromatic and heterocyclic nucleophiles leads to the formation of new imidazolidin-2-ones. The proposed method makes it quite easy to introduce the required pharmacophore group into position 4 of the imidazolidine cycle.
Synthesis and physicochemical properties of tin(IV), zirconium(IV), and hafnium(IV) 2(3),9(10),16(17),23(24)-tetrakis-(4-tritylphenoxy)phthhalocyaninates
Authors: Rumyantseva T. A , Bazanov M. I , Galanin N. E
Published: April 2024

The reaction of 4-tritylphenoxyphthalonitrile with SnCl2, ZrCl4 and HfCl4 in the presence of urea under ammonium molybdate catalysis was used to synthesize tetrakis-(4-tritylphenoxy)phthalocyaninates of tin(IV), zirconium(IV), and hafnium(IV). The complexes were characterized by spectral methods of analysis, including mass spectrometry, 1Н NMR, vibrational and electron spectroscopy. All of them form J -type dimer associates in chloroform at concentrations up to ~1.5×10-6 mol/L and lower, are not associated in a mixture of toluene and pyridine up to concentrations of ~3×10-5 mol/L and higher, have catalytic activity in electroreduction reactions of molecular oxygen. The complexes of zirconium and hafnium showed the highest activity. Tin and zirconium complexes are thermally stable in an inert atmosphere up to a temperature of 200°C.
Synthesis of phosphinic pseudomethionyl-glutamyl-histidine
Authors: Dmitriev M. E , Shevchenko K. V , Shevchenko V. P , Nagaev I. Yu. , Kalashnikova I. P , Ragulin V. V , Myasoedov N. F
Published: April 2024

The amidoalkylation reaction of a phosphonous acid containing a structural isostere of diethyl glutamiate using ethyl carbamate and 3-(methylthio)propionaldehyde was proposed for the synthesis of phosphinic pseudo-NC(O) OEt-protected Met-Glu-peptide. Subsequent adamantyl protection of the phosphorylic function and hydrolysis of carboxylic groups made it possible to obtain phosphinic pseudo-Met-[P]-Glu in the form of cyclic glutamate anhydride. It was found that the latter reacts with the third amino acid component histidine to form the phosphinic Met-[P]-Glu-γ-His tripeptide.
Synthesis of hybrid molecules based on conjugated polycyclic hydrocarbons and С60 fullerene: application of thin films based on them in organic electronics
Authors: Akhmetov A. R. , Aminov R. I. , Mullagaliev I. N. , Salikhov R. B.
Published: April 2024

Hybrid molecules based on C60 fullerene and strained polycyclic hydrocarbons were synthesized for the first time using the Bingel-Hirsch reaction. Thin films based on the synthesized hybrid compounds were obtained, and the surface morphology of these films was studied. Based on thin films of С60 fullerene adducts containing fragments of conjugated polycyclic hydrocarbons, organic field-effect transistors were fabricated. The current-voltage characteristics of transistors were measured and the mobility of charge carriers was calculated.
Structural features of monomeric octahedral d2-rhenium dioxo complexes with monoand bidentate ligands [reo2(lbi)(lmono)2], [reo2(lbi)2] (a review)
Authors: Sergienko V. S. , Churakov A. V.
Published: April 2024

Structural features of mononuclear octahedral dioxo complexes d 2-Re5+, [ReO2(Lbi)(Lmono)2], [ReO2(Lbi)2] with mono- and bidentate ligands were considered. The multiply bound Ooxo ligands are located predominantly in trans -positions to each other, with two exceptions, with the cis -orientaion of the ReO2 fragment. Rhenium atoms in most complexes have the trans -octahedral ReOoxo2X4 (X = N, P, As, O) coordination, in two cases they have the cis -octahedral ReOoxo2N4 structure. Re=Ooxo bonds in d 2-Re(V) monomeric octahedral dioxo compounds ( d average 1.772 Å) are much longer than in d 2-Re(V) monooxo complexes ( d average 1.676-1.699 Å).
Clustering and classification of red wines by physical-chemical properties using data mining methods
Authors: Bondarev N. V.
Published: April 2024

A study was preformed of 178 samples of red wines of Italian manufacturers, taken from the public repository for machine learning UCI. The methods of Data Minig made a computer analysis of the influence of 13 physico-chemical properties of the samples on the distribution of wines in three groups. The next classification models were built: factor, discriminant, canonical, MLP multilayer perceptron, Kohonen neural network SOFM, predictive (support vector method, Bayesian klаssifier, nearest neighbor method) and decision trees. The neural network classifiers SOFM 13-3, MLP 13-5-3 and clusterer SOFM 16-3 were trained. It was shown that proline, flavonoids, color intensity, proteins and alcohol determine the discriminatory power of the models.
Calculation of the formation enthalpy and the ionic equilibrium constant of organic substances by quantum chemistry methods
Authors: Maltseva V. E. , Oskorbin A. A.
Published: April 2024

Using composite methods of quantum chemical calculations and the atomization method, the values of the enthalpy of formation for a test set of 79 compounds in gas phase were calculated with an accuracy of 3.8, 4.5, 4.7 kJ/mol for the G4, G4MP2, CBS-QB3 methods, respectively. According to the results of statistical analysis of deviations of theoretical values from experimental ones, the presence of an error occurring at the geometry optimization step due to unaccounted correlation effects was revealed. For aliphatic amines and alcohols from the considered set of compounds, the values of the p K a for aqueous solutions were calculated by the G4 method including solvent effects by CPCM model. The existence of a correlation between the error in the p K a calculation and the differences in energy values between the highest occupied and lowest unoccupied molecular orbitals for conjugated acidic and basic forms in the solution phase is revealed. A method is put forward to refine the calculation results, using which the p K a values for 20 amines and 20 alcohols were determined with an accuracy of 0.67 and 0.87 p K a units, respectively.
Preparation, microstructure and properties of ceramic composite based on stabilized zirconium oxide
Authors: Bugaeva A. Yu. , Nazarova L. Yu. , Tropnikov E. M. , Shushkov D. A. , Utkin A. A. , Ryabkov Yu. I.
Published: April 2024

A pore-free ceramic composite [88ZrO2-11CeO2-Y2O3]/La0.85Y0.15Al11O18/Al2O3 with a matrix based on zirconium dioxide stabilized with cerium and yttrium oxides, filled with layered particles of lanthanum hexaaluminate and reinforced with aluminum oxide nanofibers, was obtained. The components of the composite were synthesized by the sol-gel method, with the exception of aluminum nanofibers obtained by electric explosion. The phase composition, microstructure and properties of the composite were studied depending on the combined influence of stabilizing additives and aluminum oxide nanofibers obtained by different methods. The composite is intended to be used as a ceramic material for structural and instrumental purposes.
Analytical Study of Cubature Formulas on a Sphere in Computer Algebra Systems
Authors: Bayramov R. E. , Blinkov Yu. A. , Levichev I. V. , Malykh M. D. , Melezhik V. S.
Published: April 2024

The problem of finding the weights and nodes of cubature formulas of a given order on a unit sphere that are invariant under the icosahedral rotation groups (A.S. Popov’s problem) is studied analytically in computer algebra systems. Popov’s algorithm for reducing the problem to a system of nonlinear equations is implemented in the Sage computer algebra system. It is shown that, in Sage, difficulties with studying the resulting system of nonlinear algebraic equations arise starting from the order of approximation of 23. It is also shown that Popov’s problem of this order leads to a polynomial ideal whose Gröbner basis contains polynomials with extremely large integer coefficients, which makes it quite difficult to explore with the standard tools implemented in Sage. This basis was found in our computer algebra system GInv, the new version of which was made public by one of the authors of this article in 2021. This made it possible to fully describe the set of solutions of Popov’s problem in Sage. The exact solutions found in the article are compared with the solutions found numerically by Popov. The potential of using Popov’s problem as a test problem for systems specializing in computing the Gröbner basis is discussed.
Analysis of Numerical Differential Formulas on a Bakhvalov Mesh in the Presence of a Boundary Layer
Authors: Zadorin A. I.
Published: April 2024

The paper considers numerical differentiation of functions with large gradients in the region of an exponential boundary layer. This topic is important, since the application of classical polynomial difference formulas for derivatives to such functions in the case of a uniform mesh leads to unacceptable errors if the perturbation parameter is comparable with the mesh size. The numerical differentiation formula with a given number of nodes in the difference stencil is built on subintervals covering the original interval. The accuracy of numerical differentiation formulas on a Bakhvalov mesh, which is widely used in the construction of difference schemes for singularly perturbed problems, is analyzed. For the original function of one variable, a representation in the form of a sum of regular and boundary-layer components, based on the Shishkin decomposition, is used to solve a singularly perturbed problem. Previously, such a decomposition was used to prove the convergence of difference schemes. An estimate of the error of classical polynomial formulas for numerical differentiation on a Bakhvalov mesh is obtained. The error estimate on a Bakhvalov mesh is obtained in the general case, when a derivative of an arbitrarily given order is calculated and the difference stencil for this derivative contains a given number of nodes. The error estimate depends on the order of the calculated derivative and the number of nodes in difference stencil and takes into account the uniformity in the parameter . The results of numerical experiments are presented, which are consistent with the error estimates obtained.
Integral Identity and Estimate of the Deviation of Approximate Solutions of a Biharmonic Obstacle Problem
Authors: Besov K. O.
Published: April 2024

We show that the integral identity obtained by D.E. Apushkinskaya and S.I. Repin (2020) for approximate solutions of the biharmonic obstacle problem that satisfy a pointwise constraint on the second divergence is valid for arbitrary approximate solutions. Using this result, we obtain a new estimate for the deviation of approximate solutions from exact ones in the case when the approximate solutions do not satisfy the pointwise constraint on the second divergence.
Rusanov’s Third-Order Accurate Scheme for Modeling Plasma Oscillations
Authors: Chizhonkov E. V.
Published: April 2024

A modification of the well-known Rusanov third-order accurate scheme is proposed for modeling nonrelativistic oscillations of a cold plasma. Only first- and second-order accurate schemes were used earlier for similar computations in Eulerian variables. In the case of a test problem with a smooth solution, the errors of the constructed scheme are investigated and compared with the errors of the MacCormack scheme. For the problem of free plasma oscillations induced by a short intense laser pulse, numerical results are presented concerning the conservation of energy and an additional function for both schemes and the accuracy of the electron density in the center of the domain. It is concluded that the Rusanov scheme is superior theoretically, although the MacCormack scheme is more suitable for applications, primarily, for computations of long-lived processes and cold plasma oscillations similar to actual ones. A theoretical analysis of approximation and stability, together with experimental observations of quantitative characteristics of the error for the most sensitive quantities, significantly improves the reliability of the computations.
Approximation of Functions Defined in Tabular Form: Multicriteria Approach
Authors: Nelyubin A. P. , Podinovski V. V.
Published: April 2024

A new approach to estimating approximation parameters is developed. In this approach, the distance of the approximating function from a given finite set of points is estimated by a vector criterion the components of which are the absolute values of residuals at all points. Using this criterion, the remoteness preference relation is defined, and the nondominated function with respect to this relation is considered to be the best approximating function. Approximation for several preference relations is studied, including the Pareto relation and the relation generated by the information about the equal importance of the criteria. Computational issues are considered and the relationship between the introduced approximating functions and the classical ones (obtained by the methods of least squares, least modulus, and the least maximum absolute value of deviation) are considered.
On a New Type of Unitoid Matrices
Authors: Ikramov Kh. D.
Published: April 2024

The cosquare of a nonsingular complex matrix A is defined as A in theory of A-congruences and as A in theory of Hermitian congruences. There is one more product of a similar kind, namely, A. In this paper, we discuss the following question: Is it possible to interpret such a product as a cosquare within some theory of congruences? What is this theory and how does look its canonical form?
On the Accuracy of Shock-Capturing Schemes Calculating Gas-Dynamic Shock Waves
Authors: Kolotilov V. A. , Kurganov A. A. , Ostapenko V. V. , Khandeeva N. A. , Chu S.
Published: April 2024

A comparative experimental accuracy study of three shock-capturing schemes (the second-order CABARET, third-order Rusanov, and fifth-order in space third-order in time A-WENO schemes) is carried out by numerically solving a Cauchy problem with smooth periodic initial data for the Euler equations of gas dynamics. In the studied example, the solution breaks down and shock waves emerge. It is shown that the CABARET and A-WENO schemes, which are constructed using nonlinear limiters as a stabilization mechanism, have approximately the same accuracy in the areas of shock wave influence, while the nonmonotone Rusanov scheme has significantly higher accuracy in these areas despite producing noticeable nonphysical oscillations in the immediate vicinities of shock waves. At the same time, the combined scheme obtained based on the Rusanov and CABARET schemes localizes shock wave fronts, which are captured in a non-oscillatory manner, and preserves higher accuracy in the areas of the shock influence.
Parasitic Eigenvalues of Spectral Problems for the Laplacian with Third-Type Boundary Conditions
Authors: Nazarov S. A.
Published: April 2024

Spectral problems for the Laplacian with Robin and Steklov (third-type) boundary conditions on a smooth boundary of a plane domain are considered. These conditions involve a small parameter and a coefficient of “wrong” sign, giving rise to negative eigenvalues, which are called parasitic. Such problems and eigenvalues arise in numerical schemes when regular variations in boundaries (small nonuniform shifts along the normal) are modeled by perturbations of differential operators in boundary conditions. Asymptotic expansions of some parasitic eigenvalues are constructed and justified, and a priori estimates are obtained, which help to determine their locations on the real axis and the effect exerted on the simulation errors.
Error Estimation and Optimization of the Direct Simulation Monte Carlo Method Taking into Account Spatial Regularization
Authors: Plotnikov M. Yu. , Shkarupa E. V.
Published: April 2024

The direct simulation Monte Carlo method is widely used for solving rarefied gas dynamics problems. The focus in this paper is on the study of the error introduced by spatial regularization of the interaction between two particles. Two approaches to spatial regularization and three direct simulation Monte Carlo algorithms implementing these approaches are considered. An upper bound on the error of these algorithms in the metric of the space of continuous functions is constructed, and conditionally optimal parameters that guarantee a prescribed error level in probability are obtained. Using the classical Fourier problem as an example, the error introduced by regularization is numerically investigated, and the constructed conditionally optimal parameters are tested.
Constructing Estimates of Reachability Sets in Crowd Flows Modeling
Authors: Zaitseva M. V. , Tochilin P. A.
Published: April 2024

Mathematical modeling of crowd flows in a building is studied. The study is based on a modification of the discrete CTM macromodel built on guaranteed estimates. Two methods for an approximate calculation of the reachability set—the number of people in each room at the next point in time—are proposed. Interval estimates and estimates in the form of sets of two-dimensional projections are constructed. The proposed algorithms are illustrated by numerical examples.
Application of IBSEF Method to Chaffee–Infante Equation in (1 + 1) and (2 + 1) Dimensions
Authors: Demirbilek U. , Mamedov Kh. R.
Published: April 2024

In this work, Improved Bernoulli Sub-Equation Function (IBSEF) method is proposed to seek solitary solutions of nonlinear differential equations. Chaffee–Infante equations are chosen to illustrate the effectiveness and convenience of the suggested method. Abundant new and more general exact solutions are obtained of these equations. As a result, by selecting the suitable parameters, two and three dimensional surfaces and contour plots of the results are drawn with the help of the software program.
On Simultaneous Determination of Thermal Conductivity and Volume Heat Capacity of Substance
Authors: Gorchakov A. Yu. , Zubov V. I.
Published: April 2024

The study of nonlinear problems associated with heat transfer in substance is important for practice. Earlier, the authors proposed an efficient algorithm for determining the thermal conductivity from experimental observations of the dynamics of the temperature field in an object. In this work, we explore the possibility of extending the algorithm to the numerical solution of the problem of simultaneous identification of the temperature-dependent volume heat capacity and the thermal conductivity of the substance under study. The consideration is based on the Dirichlet boundary value problem for the one-dimensional nonstationary heat equation. The coefficient inverse problem in question is reduced to a variational problem, which is solved by applying gradient methods based on the fast automatic differentiation technique. The uniqueness of the solution to the inverse problem is analyzed.
Supplement to the Classical Result of A.N. Tikhonov on Electromagnetic Sensing for a Medium with Thin Layers
Authors: Barashkov A. S.
Published: April 2024

Tikhonov’s result uses values of a function on an interval; i.e., restoring the medium requires infinitely many values of the function. In this paper, the question is posed: what information about the environment can be obtained if only several values of this function are known? The answer turned out to be most favorable. If the data array contains k function values, then the environment can be characterized by the same number of parameters.
Constructing Solutions of Cauchy Type Integral Equations by Using Four Kinds of Basis
Authors: Yaghobifar M. , Shekarabi F. Hosseini
Published: April 2024

We have four kinds of solutions for Cauchy type integral equations: by expanding on known functions and using the Maclaurin series, we can convert these four kinds of solutions into linear combinations of some elements that are basis of these solutions. Using these bases gives exact solutions for polynomials and, for some other functions, a high-accuracy approximate solution.
Exact Solutions of a Nonlinear Equation Describing Blow-Up Instability in Self-Oscillatory Systems
Authors: Aristov A. I.
Published: April 2024

A nonclassical fourth-order partial differential equation describing blow-up instability in self-oscillatory systems is studied. Several classes of exact solutions of this equation are constructed. It is shown that these solutions include ones growing to infinity in a finite time, ones bounded globally in time, and ones bounded on any finite time interval, but not globally.
On the Simulation of a Rarefied Plasma Jet on the Basis of Kinetic Equations
Authors: Abgaryan M. V. , Bishaev A. M. , Rykov V. A.
Published: April 2024

The problem of a rarefied plasma jet emerging from a stationary plasma engine is considered. The consideration is carried out entirely at the kinetic level; namely, the motion of all plasma components is described in terms of distribution functions. The system of kinetic equations should be solved together with Maxwell’s equations. Methods for solving the resulting problem are discussed.
Analysis of Defects and Harmonic Grid Generation in Domains with Angles and Cutouts
Authors: Bezrodnykh S. I. , Vlasov V. I.
Published: April 2024

A survey of works concerning difficulties associated with harmonic grid generation in plane domains with angles and cutouts is given, and some new results are presented. It is well known that harmonic grids produced by standard methods in domains with cutouts or reentrant angles (i.e., interior angles greater than π) may contain defects, such as self-overlappings or exit beyond the domain boundary. It is established that, near the vertex of a reentrant angle, these defects follow from the asymptotics constructed for the underlying harmonic mapping, according to which the grid line leaving the angle vertex is tangent to one of the angle sides at the vertex (an effect referred to as “adhesion”), except for a special case. A survey of results is given for domains z of three types with angles or cutouts (L-shaped, horseshoe, and a domain with a rectangular cutout), for which standard methods for harmonic grid generation encounter difficulties. Applying the multipole method to such domains yields a harmonic mapping for them with high accuracy: the a posteriori error estimate of the mapping in the C(z) norm is 10–7 in the case of using 120 approximative functions.
SEX AND STRAIN DIFFERENCES BETWEEN DISC1-L100P AND C57BL/6 MICE IN PASSIVE AVOIDANCE CONDITIONING DEFINATION
Authors: Chizhova N. D. , Smirnova K. V. , Dubrovina N. I. , Lipina T. V. , Amstislavskaya T. G.
Published: April 2024

Sex and strain differences in the passive avoidance learning and extinction in male and female of DISC1-L100P mice and wild-type control mice were investigated. It was shown that male and female mice of both strains were well trained in the conditioned response of passive avoidance, but differed in fear memory extinction, the ability to form a new memory trace about the safety of the previously punished dark compartment of apparatus in the procedure of repeated testing. There was a deficit of fear memory extinction in females of DISC1-L100P and C57BL/6 mice compared to males. At the same time, interstrain differences in the dynamics of passive avoidance extinction in female mice of these strains were revealed. Results also showed that DISC1-L100P males differed from C57BL/6 in terms of the time to achieve complete extinction of this reaction.
NEUROIMAGING (RESTING-STATE fMRI) AND NEUROPSYCHOLOGICAL CHARACTERISTICS OF NON-CONVERTERS WITH CLINICAL HIGH RISK FOR PSYCHOSIS
Authors: Lebedeva I. S. , Panikratova Y. R. , Abdullina E. G. , Migalina V. V. , Tikhonov D. V. , Omelchenko M. A. , Kaleda V. G.
Published: April 2024

Based on the concept of clinical high risk for psychosis, we aimed to reveal characteristics of brain functioning (resting-state fMRI) and neurocognition in 27 patients with non-psychotic mental disorders with attenuated schizophrenia symptoms who did not transit to psychosis for a long period of observation, in contrast to 24 patients with first-episode schizophrenia and 27 mentally healthy subjects. The main group was characterized by higher local coherence of BOLD signal in the right visual cortex and higher functional connectivity between the occipital component of the visual network and the right prefrontal component of the salience network (as compared to patients with schizophrenia). In both patient groups, a decreased productivity in verbal fluency tests was found. The neuroimaging and neuropsychological findings in the main group can be considered via the dichotomy of protective and pathological mechanisms in patients with high risk for psychosis.
PROLONGATION OF STIMULUS REPRESENTATION IN THE BRAIN AS A PROBABLE MECHANISM OF ASSOCIATIVE PLASTICITY IMPLEMENTATION DURING SEMANTIC LEARNING
Authors: Chernyshev B. V. , Pavlova A. A. , Rytikova A. M. , Butorina A. V. , Stroganova T. A.
Published: April 2024

It is believed that memorization of the meaning of new words occurs due to associative learning. For example, it may be matching of a word to the corresponding motor act. Synaptic plasticity in the brain develops on condition that activity of cell ensembles representing the associated events coincides in time – however, in reality, during the development of such associations, a significant time gap between the associated events is likely, which compromises necessary conditions for synaptic plasticity. We hypothesized that conditions for the development of synaptic plasticity may be created by way of prolongation in the activity of neuronal representations, thus providing for the required overlap in time at the level of neuronal ensembles. To test this assumption, we recorded magnetoencephalogram in volunteers during acquisition of associations between pseudowords and movements by four limbs. The results of the study show that there indeed occurs a significant prolongation of stimulus-induced auditory speech activation during the development of new associations. Thus, during the development of the association in the brain, the necessary conditions for Hebbian plasticity can be created – even if the events being associated are separated in time.
OFFSET RESPONSES IN CONDITIONS OF AUDITORY SPATIAL MASKING IN HUMANS
Authors: Petropavlovskaia E. A. , Shestopalova L. B. , Salikova D. A. , Semenova V. V.
Published: April 2024

The influence of relative spatial positions of sound stimuli and background masker on the event related potentials (ERPs) evoked by sound offset was investigated. Sound stimuli were presented dichotically, the position of sound images was manipulated using interaural level differences. Test signals were presented in silence or against the background of a masker. Signal and masker were either co-located or separated by 90 or 180 deg of azimuth. Co-location of signal and masker resulted in amplitude decrease and latency increase in the N1, P2 and N2 components. When angular distance between signal and masker increased, the amplitude recovered almost to the initial level and the latency of all components became shorter. The present findings are in line with the view that offset response is essential for target stimulus detection in the background noise.
On the Existence of Solutions of the Neumann Problem for the
-Laplacian on Parabolic Manifolds with a Model End
Authors: Brovkin V. V
Published: April 2024

A criterion for the existence of solutions of the second boundary value problem for the -Laplacian on Riemannian parabolic manifolds with a model end is obtained.
On One Type of Oscillating Solutions of a Second-Order Ordinary Differential Equation with a Three-Position Hysteresis Relay and a Perturbation
Authors: Evstaf'eva V. V , Kamachkin A. M , Potapov D. K
Published: April 2024

A second-order ordinary differential equation with a three-position hysteresis relay characteristic and a periodic perturbation function is considered. The existence theorem is proved for an oscillatory solution with a complete traversal of the characteristic with a possible exit into its saturation zones in some finite time and with a closed phase trajectory of an arbitrary shape. Sufficient conditions for the existence of periodic solutions with arbitrary and symmetric phase trajectories are established, as well as conditions for the nonexistence of a periodic solution with a symmetric phase trajectory. Numerical examples are given.
A Time-Nonlocal Inverse Problem for the Beam Vibration Equation with an Integral Condition
Authors: Durdiev U. D
Published: April 2024

We study the direct problem for transverse vibrations of a homogeneous beam of finite length with time-nonlocal conditions and obtain necessary and sufficient conditions for the existence of its solution. For the direct problem, the inverse problem of determining the time-dependent coefficients of the lower derivative and the right-hand side in the equation is studied. The existence and uniqueness of the solution of the inverse problem are proved. The solution is based on separation of variables, which is used to reduce the problems to an integral equation and a system of integral equations.
Smooth Solutions of Hyperbolic Equations with Translation by an Arbitrary Vector in the Free Term
Authors: Zaytseva N. V , Muravnik A. B
Published: April 2024

We construct three-parameter families of solutions of hyperbolic differential-difference equations in a half-space with a general shift operator in the free term (or in a nonlocal operator potential). It is proved that the solutions obtained are classical if the real part of the symbol of the corresponding differential-difference operators is positive. Classes of equations for which the indicated condition is satisfied are given.
Pullback Attractors of the Bingham Model
Authors: Zvyagin V. G , Ustyuzhaninova A. S
Published: April 2024

Based on the theory of trajectory pullback attractors, we study the qualitative behavior of weak solutions for the Bingham model with periodic conditions in the space variables. For the model under consideration, a family of trajectory spaces is introduced and the existence of pullback attractors is proved.
On the Unique Solvability of Initial–Boundary Value Problems for Parabolic Systems in Bounded Plane Domains with Nonsmooth Lateral Boundaries
Authors: Baderko E. A , Sakharov S. I
Published: April 2024

We consider the first and second initial–boundary value problems for inhomogeneous second-order parabolic systems with Dini continuous coefficients under nonzero initial conditions in bounded domains on the plane with nonsmooth lateral boundaries that, in particular, admit cusps. Theorems are proved on the unique classical solvability of these problems in the space of functions that are continuous together with their first spatial derivatives in the closure of these domains.
Linear Recurrent Equations in the Space of Convex Compact Sets and the Diameters of Their Solutions
Authors: Voydelevich A. S
Published: April 2024

In the space of convex compact sets with the Minkowski addition operation and the operation of multiplication of a matrix by a set, we consider linear recurrent equations of the first order. We give a complete description of such equations whose all solutions have a constant diameter. For equations of a special form, the Lyapunov exponents of the sequences of diameters of their solutions are calculated.