bluuebunny/crossref_metadata_2025 huggingface dataset:
Far Fields at Interface between an Infinitely Deep Ocean and Ice Excited by a Localized Source
Authors: Bulatov V. V. , Vladimirov I. Yu.
Published: April 2024

The problem of constructing asymptotics of the far wave fields that arise at the interface between ice and an infinitely deep liquid in the flow around a localized source is solved. An integral representation of the solution is obtained, and an asymptotic representation of the solution for supercritical modes of wave generation is constructed using the stationary phase method. The exact and asymptotic results are compared, and it is shown that the asymptotics far from the source make it possible to describe the amplitude-phase structure of far wave fields.
LASER GENERATION OF COLLOIDAL NANOPARTICLES IN LIQUIDS: KEY PROCESSES OF LASER DISPERSION AND MAIN CHARACTERISTICS OF NANOPARTICLES
Authors: NASTULYAVICHUS A. A. , KUDRYASHOV S. I. , EMELYANENKO A. M. , L. B. BOINOVICH L. B.
Published: April 2024

The processes of laser dispersion of materials for high-performance generation of colloidal nanoparticles in liquids have been considered. Various laser and material parameters affecting this process have been studied. Efficiencies and ergonomics of the generation of colloidal nanoparticles with the help of laser systems having nano-, pico-, and femtosecond pulse durations have been compared using optical and mass criteria by the example of laser ablation of a chemically inert model material (gold) in distilled water without the use of chemical stabilizers. The main characteristics of gold and silver nanoparticles obtained by ablation in water using pulsed laser radiation of different durations have been comprehensively compared. The types of colloidal interactions between nanoparticles in aqueous media have been discussed, and the contributions of structural and ion-electrostatic interactions to the long-term stability of gold and silver nanoparticle dispersions have been analyzed.
ESTIMATION OF THE SHAPE FACTOR OF AGGREGATES IN SELF-ASSOCIATING SYSTEMS BASED ON METALLOSURFACTANTS
Authors: ZHIL’TSOVA E. P. , ISLAMOV D. R. , L. YA. ZAKHAROVA L. YA.
Published: April 2024

A mathematical evaluation of the shape factor of aggregates formed by amphiphilic compounds in an aqueous medium has been carried out on the basis of dynamic light scattering data for self-associating systems based on metallocomplexes of alkylated derivatives of 1,4-diazabicyclo[2.2.2]octane with Ag(I) and Gd(III) nitrates, a ligand, and a ligand–inorganic salt mixture. Micellar and vesicular approximations have been used. A relationship between the shape factor and the parameters of the water pool of an aggregate has been shown for vesicular systems.
Dynamic Properties of Pulmonary Lipid Monolayers on the Surfaces of Sodium Polystyrene Sulfonate and Polydiallyldimethylammonium Chloride Solutions
Authors: Bykov A. G. , Panaeva M. A.
Published: April 2024

Pulmonary surfactant, which is a complex mixture of lipids and proteins, plays a key role in the functional properties of the respiratory system. Lipids form complexes with proteins to maintain low values of surface tension at continuous compression/expansion deformations. However, interactions that lead to the complexation still remain to be unknown thus significantly hampering the development of synthetic analogs of the natural pulmonary surfactant. In this work, the methods of surface rheology and ellipsometry have been employed to study the dynamic properties of model phospholipid monolayers applied onto the surfaces of synthetic polyelectrolyte solutions. It has been shown, that electrostatic or hydrophobic interactions between lipids and macromolecules are insufficient for the efficient complexation and maintenance of low surface tension values.
CATION-DEFICIENT SODIUM–GADOLINIUM MOLYBDATES OF VARIABLE COMPOSITION. SIMULATION OF THE PROPERTIES AND LOCAL STRUCTURE
Authors: Dudnikova V. B. , Antonov D. I. , Zharikov E. V. , Eremin N. N.
Published: April 2024

Cation-deficient Na2–3xGdxMoO4 solid solutions in the NaGd(MoO4)2–Gd2(MoO4)3 system have been simulated by the interatomic potentials method. The parameters and volume of unit cell, as well as density, bulk modulus, enthalpy, vibrational entropy, and heat capacity in dependence of the composition are determined. Temperature dependences of the heat capacity and vibrational entropy are plotted. The local structure of the solid solutions has been studied. It is shown that the vacancy–oxygen distances are on average 5.0% larger than the Na–O distances and 11.8% larger than the Gd–O distances. The sizes of these coordination polyhedra slightly increase with an increase in the gadolinium content, which is accompanied by an increase in the unit-cell size. The parameter c increases with a higher rate as compared to a, which is indicative of distortion of the unit cell and polyhedra.
STRUCTURAL COMPLEXITY OF MOLECULAR, CHAIN, AND LAYERED CRYSTAL STRUCTURES OF NATURAL AND SYNTHETIC ARSENIC SULFIDES
Authors: Banaru D. A. , Aksenov S. M. , Yamnova N. A. , Banaru A. M.
Published: April 2024

A ladder-wise calculation scheme has been developed for the structural complexity of heterodesmic crystal structures, with crystal interpreted as a system of contacting molecules, chains, and layers. In the last stage of ladder-wise calculation the structural complexity of the main motif is summed with the complexity of the contacts beyond the main motif in correspondence with the strong additivity rule. The application potential of the scheme is demonstrated, and the calculation results for the crystal structures of natural and synthetic arsenic sulfides are presented. The coordination of molecules and chains that is necessary for calculating the complexity of contacts beyond the main motif is determined by the method of Voronoi–Dirichlet polyhedra.
IN-LINE METHOD OF X-RAY PHASE-CONTRAST MICRO-CT USING A WIDE-FOCUS LABORATORY SOURCE
Authors: Krivonosov Yu. S. , Buzmakov A. V. , Asadchikov V. E. , Fyodorova A. A.
Published: April 2024

An experimental implementation of the “in-line” method of X-ray phase contrast using a standard wide-focus X-ray tube as a polychromatic source is described. Using the proposed experimental scheme, in vitro tomographic measurements of a sample of human brain pineal gland are carried out, and the morphological structure of the soft tissues of this organ is visualized based on the results obtained. The advantage of phase-contrast tomography in comparison with traditional absorption tomography for studying the structural features of soft tissues is experimentally demonstrated. The “in-line” phase-contrast scheme, implemented on a laboratory setup, allows tomographic study of samples with linear dimensions of several millimeters and a resolution of ∼20 μm.
COMPARISON OF THE NUMERICAL AND ANALYTICAL CALCULATIONS OF THE RESOLUTION FUNCTION FOR A POWDER NEUTRON DIFFRACTOMETER
Authors: Drozhzhov K. A. , Kibalin Yu. A. , Tarnavich V. V. , Golosovsky I. V.
Published: April 2024

The resolution of the high-intensity diffractometer, developed for the PIK reactor (Gatchina), is calculated both numerically and analytically. These two approaches give different results. All neutron trajectories calculated numerically are limited by the geometry of optical elements. Therefore, the diffraction profile has a trapezoidal shape, which can be seen well at large diffraction angles. Analytical formulas yield a Gaussian line profile. The difference in profiles leads to a difference in the resolution curves calculated numerically and analytically. This difference is especially pronounced for the diffractometers with medium and low resolution, optimized to the maximum intensity.
Study of the Effect of Inverse Magnetostriction in Ferromagnet/Ferroelectric Heterostructures Using Ab Initio Calculations
Authors: Gumarova I. I. , Evseev K. V. , Kamashev A. A. , Mamin R. F.
Published: April 2024

Fe/BaTiO3, Fe/SrTiO3, Co/BaTiO3, and Co/SrTiO3 heterostructures, which exhibit magnetoelectric effect, have been investigated. It is shown that the magnetic properties of thin ferromagnetic films can be controlled using an external electric field. The structural, electronic, and magnetic properties of the heterostructures have been investigated applying ab initio calculation methods. It is shown that, using the inverse piezoelectric effect, one can reduce the absolute value of the ferromagnet magnetization vector. This approach may be a basis for controlling the properties of one of the ferromagnetic layers of a superconducting spin valve and, as a consequence, the superconducting properties of the valve.
Structural Transformation of Relaxor PbMg1/3Nb2/3O3 under Electric Field Switching
Authors: Vakhrushev S. B. , Bronwald Yu. A. , Udovenko S. A. , Koroleva E. Yu. , Molokov A. Yu.
Published: April 2024

One from the most important features of relaxors is the possibility of inducing a stable ferroelectric phase in them by applying an electric field. This induced phase transition has been multiply investigated; in particular, the structural changes during the transition and its kinetics were traced. However, the processes occurring under electric field switching remain little-studied, and the structural transformation during switching generally has not been investigated at all. To fill in this gap, the temporal evolution of the pattern of Bragg and diffuse X-ray scattering in classical relaxor PbMg1/3Nb2/3O3 at T = 175 K during multiple switching of the direction of a dc external field E = ± 6.25 kV/cm has been traced. It is shown that the glasslike state decays and a mixed ferro-glass phase is formed after switched on a field. Switching the field sign leads to a rise of dipole-glass correlations; however, no signs of occurrence of an inhomogeneous state with limited regions of dipole-glass and ferroelectric phases were found. Switching the field to the initial direction causes rapid formation of the ferroelectric phase, without any rise in the dipole-glass correlations. A repeated switching leads to a decrease in the Bragg scattering intensity, related to the long-range order. This effect is presumably due to the occurrence of random weakly correlated ionic displacements, violating the long-range order.
Thermally Induced Pulsed Processes in Strontium Barium Niobate Single Crystals
Authors: Bolshakova N. N. , Burtsev A. V. , Pedko B. B. , Semenova E. M.
Published: April 2024

A brief analytical review of the literature data on the jump switching processes in classical ferroelectrics and new results of the experimental study of the thermally induced pulsed processes in the strontium barium niobate relaxor ferroelectric crystals are presented. The mechanisms of their occurrence in different temperature ranges are discussed based on the data of spectral analysis of the parameters of pulsed processes.
Structural Study of the Light-Harvesting Complex LH2 from the Purple Sulfur Bacteria Ectothiorhodospira haloalkaliphila by Cryoelectronic Microscopy
Authors: Burtseva A. D. , Baymukhametov T. N. , Ilyasov I. O. , Bolshakov M. A. , Moskalenko A. A. , Boyko K. M. , Ashikhmin A. A.
Published: April 2024

The primary processes of photosynthesis for purple photosynthesising bacteria occur in light-harvesting (LH) complexes. The LH2 complex contains polypeptides; bacteriochlorophyll; and, in most cases, carotenoids. There are three known spatial structures of LH2 complexes from purple nonsulfur bacteria; however, high-resolution structures have not been established for purple sulfur bacteria. The results of the structural study of two light-harvesting complexes LH2 from purple sulfur bacteria Ectothiorhodospira haloalkaliphila by cryoelectronic microscopy are reported. Images of carotenoid-containing (LH2+) and carotenoidless (LH2–) variants of the complex, demonstrating a characteristic architecture of the objects of this type, are obtained. A 3D reconstruction of LH2+ is performed with a resolution of 4.5 Å; it coincides with the previously established crystal structure. The presence of particles of different morphology is shown for LH2–.
Structural Reorganization of Cell Membrane Models Caused by the Anticancer Antibiotic Doxorubicin
Authors: Novikova N. N. , Kovalchuk M. V. , Rogachev A. V. , Malakhova Yu. N. , Kotova Yu. O. , Gelperina S. E. , Yakunin S. N.
Published: April 2024

The molecular mechanisms of the interaction of anticancer antibiotic doxorubicin with lipid cell membrane models have been investigated using grazing incidence X-ray diffraction (XRD) and X-ray reflectivity (XRR). The model systems were monolayers of four types of phospholipids, related to the main components of animal cell membranes. New information on the processes of damage of phospholipid monolayer lattice caused by doxorubicin is obtained. It is established that the action of doxorubicin on anionic phospholipid monolayers is determined by the electrostatic interaction: positively charged doxorubicin molecules are incorporated between negatively charged phospholipid functional groups. In the case of neutral phospholipids the key role belongs to the hydrophobic interaction: doxorubicin molecules are coordinated with phospholipid hydrocarbon tails in disordered regions.
Adsorption of Rare Earth Metal Cations by Base Metal Sulfides in the Broken Spur and TAG Hydrothermal Fields, Atlantic Ocean
Authors: Novikov G. V. , Lobus N. V. , Shulga N. A. , Bogdanova O. Yu.
Published: April 2024

The article presents the results of sorption of rare earth metal cations on samples of deepsea polymetallic sulfides of the hydrothermal fields of the Broken Spur and TAG of the Mid-Atlantic Ridge. The main minerals of these samples were respectively marcasite, pyrrhotine, pyrite, sphalerite and chalcopyrite, pyrite, and marcasite. It has been established that these sulfide minerals of iron, copper and zinc are natural adsorbents. The exchange capacity of sulfide minerals for rare earth metal cations is in the range of 0.006‒0.061 mg-eq/g. The exchange complex of sulfide minerals consists of cations of alkaline, alkaline-earth metals and basic cations of metals of the crystal lattice – Fe, Zn, Cu (in very limited quantities). The mechanism of absorption of rare earth metal cations is ion-exchange, equivalent to the exchange cations of sulfide minerals. It was found that in the composition of sulfide minerals, rare earth metal cations are almost completely in sorbed form (more than 90% of the total amount); The chemically bound form can be, apparently, only for Lu and Dy cations. The mineral composition of sulfide deposits is preserved in the products of exchange reactions, new phases do not appear.
Role of the Structural and Functional Genes Encoding Heat Shock Proteins in Biosurfactant Synthesis by Rhodococcus pyridinivorans 5Ap
Authors: Bukliarevich H. A. , Titok M. A.
Published: April 2024

Abstract—The role of groESL and dnaJ structural genes and hrcA regulatory gene, encoding the synthesis of heat shock proteins, in biosurfactant synthesis by R. pyridinivorans 5Ар was determined. The CIRCE binding sites for the regulatory protein coded by hrcA gene were revealed in the promoter regions of groESL, groEL2, and fmdB genes. GroESL and groEL2 genes expression during the late exponential phase in the medium with hexadecane at 42°C was higher than at 28°C (4.4 and 5.3 times, respectively). At the same time, no changes in expression of hrcA and fmdB genes were observed at two different temperature modes (28 and 42°C). In the absence of the negative regulator HrcA, groESL expression increased 14.4 and 3.5 times, that of groEL2, 9.6 and 2.7 times, and that of fmdB, 1.82 and 2.52 times at 28 and 42°C, respectively. Products of dnaJ and hrcA genes were required for trehalolipid synthesis at different temperature modes, with their role increasing at higher temperature (synthesis of trehalolipids by the mutant with impaired dnaJ gene decreased 1.8 and 2.5 times compared to 1.5 and 6.6 times, for the mutant with impaired hrcA at 28 and 42°C, respectively). At the same time, emulsifying activity of all mutant variants did not change at 28°C and decreased 1.4 and 1.9 times 42°C for the mutants with impaired groESL and hrcA genes, respectively. Our results indicated the complex chemical nature of the biosurfactants produce by R. pyridinivorans 5Ар (emulsifiers, including trehalolipids and compounds of other chemical composition). The Gro chaperones and the HrcA regulatory protein play the key roles in synthesis of these compounds at different temperature modes, while the dnaJ is required only for trehalolipid synthesis.
High Efficiency of Removal of Pathogenic Microorganisms at Wastewater Treatment Plants in the City of Moscow
Authors: Begmatov Sh. A. , Dorofeev A. G. , Pimenov N. V. , Mardanov A. V. , Ravin N. V.
Published: April 2024

Abstract—While most pathogenic bacteria are efficiently removed from wastewater during biological treatment, some pathogens, notably Arcobacter, may be abundant in the purified water. Using 16S rRNA gene profiling, the composition of microbial communities of municipal wastewater in the city of Moscow was studied before and after biological purification at the Lyubertsy wastewater treatment plant. Fecal contaminants of the genera Acinetobacter, Aeromonas, Arcobacter, Bacteroides, Streptococcus, and Veillonella, which include human pathogens, predominated in the influent wastewater. After treatment, the relative abundance of these bacteria decreased by 50‒100 times. Predominant organisms in the microbiome of the effluent water were bacteria characteristic of activated sludge, including the nitrifiers of the genera Nitrospira and Nitrosomonas, as well as phosphate- and glycogen-accumulating microorganisms. Thus, pathogenic bacteria, including Arcobacter, are effectively removed at the Moscow wastewater treatment plant.
Osmolytes and Lipids of the Conidia of the Xerohalophilic Micromycete Aspergillus penicillioides
Authors: Danilova O. A. , Ianutsevich E. A. , Antropova A. B. , Tereshina V. M.
Published: April 2024

Abstract—Investigation of the lipid and osmolyte composition in conidia of the xerohalophile Aspergillus penicilloides grown on media with high concentrations of NaCl and glycerol is important for the understanding of the functions of these compounds in the adaptation of the extremophile. Conidia of the fungus grown on a medium with glycerol contained up to 15% of the dry mass of carbohydrates and polyols (CaP) of the cytosol, with predominance of glycerol (60% of the total) in their composition, while on a medium with salt, the proportion of glycerol did not exceed 20%, and the amount of CaP was 10%. On both media, the proportion (20%) and amount (2.5%) of trehalose were the same; the proportion of polyols was thus about 80%, although their composition was different, indicating a possible synergy between trehalose and polyols in adaptation. Both variants of conidia were characterized by a low content of both membrane and storage lipids, represented mainly by triacylglycerides. Phosphatidylcholines and sterols were the predominant membrane lipids of the fungal conidia, regardless of the composition of the medium, which indicated high stability and conservatism of the lipid bilayer. The constancy of the composition of membrane and storage lipids and their low content, the high level of CaP, and significant differences in their composition indicate the key role of osmolytes in the adaptation of fungal conidia to various environmental conditions.
Hall Effect in Magnetic Tunnel Junctions
Authors: Karashtin E. A , Gusev N. S , Pashen'kin I. Yu , Sapozhnikov M. V , Fraerman A. A
Published: April 2024

We have constructed a theory of the Hall effect appearing during the passage of current in a magnetic tunnel junction due to the spin–orbit interaction in an insulator barrier in the approximation of a delta-shaped barrier potential. Both the normal Hall current flowing in metal banks as a result of asymmetric scattering in the tunneling barrier and the anomalous current existing only in the tunneling barrier due to the presence of the spin–orbit interaction in it are taken into account. We have considered the Rashba interaction that can be of intrinsic origin (noncentrosymmetric form of the barrier) or can be induced by an extraneous electric field emerging as a result of application of a potential difference to the barrier. Such a field can reach a value on the order of 109 W/m, which is close to intrinsic atomic fields. The Hall current has both linear and quadratic components in the voltage applied to the tunnel junction. The existence of the nonlinear Hall voltage corresponding to it has been illustrated experimentally in a CoFeB/MgO/Pt tunnel junction, in which the transverse (Hall) voltage has been measured in the Pt layer.
Peculiarities of Formation of Flat Inhomogeneous Structures in Nanoscale Magnetic Films
Authors: Magadeev E. B , Vakhitov R. M , Kanbekov R. R
Published: April 2024

Stability conditions are studied for vortex-like inhomogeneities in perforated ferromagnetic films with strong easy plane uniaxial anisotropy. It is shown that nontrivial magnetic structures characterized by the absence of out of plane magnetization can be observed at absolute values of the anisotropy constant exceeding a certain threshold value. Possible (analytical, numerical, and empirical) methods for calculating this threshold value are developed. Universal estimates of the minimum permissible value of the anisotropy constant are obtained in a number of important cases. Feasible scenarios for the loss of stability of the magnetic structure under the variation of the material parameters of the film are analyzed.
Influence of Polymerization Conditions on Magnetic Properties of a Ferrocomposite
Authors: Radushnov D. I , Solov'eva A. Yu , Elfimova E. A
Published: April 2024

This paper is devoted to a theoretical study of the magnetic properties of an ensemble of single-domain interacting magnetic nanoparticles embedded in an immobile polymer matrix. This model is typical for the description of magnetically active polymer ferrocomposites widely used in industrial and biomedical applications. A ferrocomposite is assumed to be produced by carrier medium solidification in a ferrofluid in an external magnetic field hp at a polymerization temperature Tp; after carrier fluid solidification, the nanoparticles retain the spatial distribution and orientation of their easy magnetization axes that they had before carrier medium solidification. The contribution of interparticle dipole–dipole interactions to the static magnetization of a ferrocomposite as a function of the magnetic field strength h and polymerization field hp has been studied separately. The effects of the polymerization temperature and the size of magnetic nanoparticles on the magnetic properties of a ferrocomposite have been analyzed. The analytical expressions for the magnetization and initial magnetic susceptibility presented in the paper make it possible to predict the magnetic properties of a ferrocomposite as a function of its intrinsic characteristics and synthesis conditions, which is a theoretical basis for the production of ferrocomposites with a predetermined magnetic response in a given magnetic field.
Investigation of Josephson Contacts Pb0.6In0.4/KFe2As2 and KFe2As2/KFe2As2 and Order Parameter Symmetry Check
Authors: Golubkov M. V , Stepanov V. A , Sadakov A. V , Usol'tsev A. S , Morozov I. V
Published: April 2024

The characteristics of point Josephson contacts Pb0.6In0.4/KFe2As2 and KFe2As2/KFe2As2 have been studied. The temperature dependences of characteristic contact voltages VC(T) and the dependences of the first current step amplitudes in I–V characteristics on the power of 7.6-GHz electromagnetic radiation have been measured. It has been found that VC(T) curves for all contacts can be described in terms of the SIS*IS contact model (S, I, and S* stand for superconductor, insulator, and superconductor with a lower critical temperature, respectively) for superconductors with the s-symmetry of order parameter. It has been proved that the current step oscillation period as a function of microwave power can be exactly approximated with the resistive model of contact with IS = ICsin(φ). Obtained data are consistent with the normal s-symmetry of order parameter.
Formation, Diffusion, and Growth of Gas Bubbles in γ-Uranium with the Excess of Interstitial Atoms: Relation between Molecular Dynamics and Kinetics
Authors: Lobashev E. A , Antropov A. S , Stegaylov V. V
Published: April 2024

The formation of gas nanobubbles through the merging of individual fission products of uranium is an important process for the evolution of nuclear fuels. The theoretical description of this process is very difficult because both the dynamics of individual atoms in the lattice and the kinetics of evolution of an ensemble of bubbles should be taken into account within a unified model. Such a model is constructed in this work on the basis of molecular dynamics simulations for xenon bubbles in bcc uranium in the case of the excess of interstitial atoms in the crystal matrix. The analysis is based on the molecular dynamics simulation of the nonequilibrium process of formation of xenon nanobubbles from individual Xe atoms dissolved in the crystal matrix. A relation between the size of bubbles and the number of gas atoms in them, as well as the dependence of the diffusion coefficient of bubbles on their radius and the number of interstitial atoms in the γ-U matrix, has been analyzed. A kinetic model of evolution of the ensemble of bubbles has been proposed to describe the molecular dynamics results and to extrapolate them to long times.
On the Problem of Bound States of Electron and Hole in Transition Metal Dichalcogenides
Authors: Krachkov P. A , Terekhov I. S
Published: April 2024

The interacting electron and hole in transition metal dichalcogenides are considered. To investigate the interaction the Bethe-Salpeter equation was obtained in the leading order in the interaction potential. It is shown that the behavior of the potential at short distances significantly affects the binding energy of the electron and the hole. We demonstrate that the expansion of the Bethe-Salpeter equation in the small coupling constant does not contain singular operators. Therefore, the binding energy of the electron and the hole does not contain the regularization parameter. Using the perturbation theory in the coupling constant we analytically calculated the energies of the ground and first excited states of the exiton. For arbitrary values of the coupling constant, the energies of the bound states of the electron and the hole are obtained numerically. The critical values of the coupling constant for the Coulomb potential and for the exponentially decreasing potential are also found numerically.
Shock-Wave Compression of Nitrogen Fluid in the Pressure Range 140–250 GPa
Authors: Zhernokletov M. V , Kovalev A. E , Novikov M. G , Gryaznov V. K , Iosilevskiy I. L , Shutov A. V
Published: April 2024

The results of a series of experiments on the shock compression of a dense nitrogen fluid, which is preliminarily statically compressed to an initial density ρ = 0.8, 0.65, and 0.5 g/cm3, to pressures of 140–230 GPa in hemispherical shock-wave generators are discussed. The experiments are carried out in continuation and development of the earlier series of experiments on the shock compression of liquid nitrogen to pressures of 100–330 GPa, which were performed at VNIIEF (Sarov) in 2008–2010. The purpose of our experiments is to verify and confirm the earlier revealed limiting compression of nitrogen to a limit close to an ideal gas (ρ/ρ0 ≈ 4.2) and the remarkable subsequent quasi-isochoric segment of the Hugoniot adiabat in the pressure range 100–330 GPa. The experimental data obtained are compared with the results of theoretical calculations performed with various models of the equation of state of a nonideal nitrogen plasma
Critical Point in the Curve of First-Order Magnetic Phase Transition
Authors: Valiev E. Z
Published: April 2024

A magnetic state diagram for ferromagnets exhibiting a first-order phase transition in a magnetic field has been calculated. Calculations have been made using the exchange-striction model of a ferromagnet. It has been shown that the curve of first-order magnetic phase transition ends up at a critical point (Hcr, Tcr) that is similar to the critical point of the liquid–gas transition on the (T, P) plane. Analytical expressions for thermodynamic quantities, namely, magnetic susceptibility, specific heat, and compressibility, which anomalously grow near the critical point, have been derived. Calculation results have been compared with available experimental data for La(Fe0.88Si0.12)13 ferromagnet, which experiences the first-order magnetic phase transition.
Vortices on the Free Surface of a Normal Helium He-I Layer in a Wide Cell
Authors: Levchenko A. A , Mezhov-deglin L. P , Pel'menev A. A
Published: April 2024

The appearance of a thermogravitational convective flow in the bulk of a layer of normal liquid helium He-I h ≈ 1–3 cm deep in a wide cylindrical cell, which is heated from above in the gravity field in the temperature range Tλ ≤ T ≤ Tm, is accompanied by the excitation of a vortex flow on the free surface of the liquid. Here Tλ = 2.1768 K is the temperature of transition of liquid 4He from the superfluid He-II to the normal He-I state at the saturated vapor pressure, and Tm ≈ 2.183 K is the temperature at which the He-I density passes through a maximum. Bulk convection serves as a source of energy pumped into the vortex system on the surface of He-I. The nonlinear interaction of vortices on the surface with each other and with convective vortex flows in the bulk of the layer leads to the formation of two large-scale vortices (vortex dipole) on the surface of He-I, and their sizes are limited to the diameter of the working cell and several times exceed the layer depth. This behavior corresponds to the transition from the vortex flow mode on “deep water” (vortices on the surface of a three-dimensional liquid layer) to vortices on the surface of “shallow water” (vortices on the surface of a two-dimensional layer) in time. When the layer is heated further above Tm, the convective flows in the bulk decay quickly, but the vortex motion on the surface of a two-dimensional He-I layer is retained. In the absence of energy pumping from the bulk, the total energy of the vortex system on the surface of a shallow water layer decreases in time according to a near-power law because of the nonlinear interaction of large-scale vortices with each other and friction against the cell walls. As a result, during long-term observations, small-scale vortices with sizes comparable to or less than the layer depth again begin to prevail on the surface of He-I, which corresponds to the transition from a two-dimensional to a three-dimensional liquid layer. The energy of the vortex flow on the surface of a deep water layer decreases according to a near-exponential law. Thus, long-term observations of the dynamic phenomena on the free surface of an He-I layer several centimeters deep in a wide temperature range above Tλ allowed us, for the first time, to study the excitation, evolution, and decay of the vortex flows on the surface of a deep or shallow water layer in one experiment.
Terahertz Time-Domain Spectroscopy (THz-TDS) of LED Heterostructures with Three and Five InxGa1 – xN/GaN Quantum Wells
Authors: Burmistrov E. R , Avakyants L. P
Published: April 2024

Using terahertz time-domain spectroscopy (THz-TDS), we have detected resonance frequencies of plasmon oscillations excited in heterostructures with multiple InxGa1 – xN/GaN quantum wells by laser pulses with a duration of 130 fs in the temperature range from 90 to 170 K. The fast Fourier transform of temporal forms of terahertz pulses has made it possible to obtain frequency spectra of the power and of the phase shift of terahertz radiation, the interpretation of which has allowed us to estimate the quasi-momentum relaxation time (τ = 10–12 s), mobility (μ = 4 × 103 cm2/(V s)), and effective mass (m* = 0.45m) of majority charge carriers in these heterostructures. Based on the frequency spectra of power and phase shift of terahertz radiation, we have obtained the temperature dependences of the effective mass and relaxation time of the quasi-momentum of a 2D electron gas (2DEG). The 2DEG mobility value obtained by the THz-TDS method is in good agreement with the Hall measurement data.
Finite Time Effects in Single and Double Compton Scattering
Authors: Dubrovich V. K , Zalyalyutdinov T. A
Published: April 2024

The process of Compton scattering by a free electron with subsequent reemission of one or two photons is considered in the assumption of finite interaction time. The corresponding cross sections are obtained in the framework of relativistic quantum electrodynamics using a modified form of fermion propagator with complex transmitted momentum. It is shown that finite time effects can be observable at sufficiently low energies of scattered photons. The proposed method also regularizes arising infrared divergence in the cross section of the double Compton effect. Possible experimental verification of considered theoretical approach is discussed.
Structure of Ion–Molecular H+(H2O)n (n = 2–6) Complexes and the Thermodynamic Characteristics of Proton Hydration in Gas Atmosphere
Authors: Reshetnyak V. V. , Reshetnyak O. B , Filippov A. V.
Published: April 2024

The isomers of ion–molecular H+(H2O)ncomplexes including up to six water molecules have been studied using quantum chemistry methods. The atomic positions in the isomers corresponding to the global and deepest local minima of potential energy are calculated using the basin-hopping algorithm. The activation energies of some configuration transformations are estimated. The thermodynamic characteristics of the clustering and decomposition of complexes are determined in a harmonic approximation, and they are in good agreement with experimental data. The possibility of simplifying the theoretical investigation of reactions by averaging the thermodynamic characteristics over various channels for energetically close isomers is shown. A weak dependence of the entropy of a reaction on the complex size has been found. A simplified model is proposed to explain the calculation results, and its use for estimating the entropies of complex clustering and decomposition reactions gives good agreement with the experimental results.
Analysis of the Result of the Neutrino-4 Experiment Together with Other Experiments on the Search for Sterile Neutrinos within the 3 + 1 Neutrino Model
Authors: Serebrov A. P. , Samoylov R. M. , Chaykovskiy M. E.
Published: April 2024

The correspondence of the results obtained in the Neutrino-4 experiment with the results of the NEOS, DANSS, STEREO, and PROSPECT experiments at reactors, the MiniBooNE, LSND, and MicroBoone experiments at accelerators, and the IceCube and BEST experiments with a51Cr neutrino source is analyzed. The agreement between the results of the Neutrino-4 experiment, the BEST experiment, and the gallium anomaly on the mixing angle is discussed. The discrepancy between the results of the listed direct experiments with the results of the reactor anomaly, as well as with constraints from solar and cosmological data, is discussed. It is shown that the results of these direct experiments on the search for sterile neutrinos and the IceCube experiment do not contradict the Neutrino-4 experiment within the 3+1 neutrino model within 3σ contours of experimental errors. The sterile neutrino parameters from the Neutrino-4 and BEST experiments make it possible to estimate the sterile neutrino mass asm4= (2.70 ± 0.22) eV and the effective mass of the electron neutrino asm4νe= (0.86 ± 0.21) eV. The matrix of the absolute values of the 3 + 1 neutrino model mixing parameters and the mixing scheme are presented.
Classification and Dynamics of Ultralean Hydrogen–Air Flames in Horizontal Cylindrical Hele–Shaw Cells
Authors: Moskalev P. V. , Denisenko V. P. , Kirillov I. A.
Published: April 2024

Using the successively inverted projection method, we studied the dynamics of ultralean hydrogen–air flames propagating freely in a horizontal cylindrical Hele–Shaw cell. To quantify the two revealed characteristics of the flame dynamics—the dependence of the average flame velocities on time and the dependence of the initial flame velocity on the stoichiometry of the initial hydrogen–air mixture—we proposed time and stoichiometric scaling relations. The first relation approximates the dependence of the path of the flame front in hydrogen–air mixtures with an initial hydrogen concentration exceeding a certain critical value. The second relation approximates the dependencies of the initial flame front velocities on the hydrogen concentration. The general relationships for topologically different types of ultralean hydrogen–air flames can be interpreted as additional evidence of the presence of a general mechanism for the transition from discrete fronts of isolated drifting ball flames to a quasi-continuous deflagration flame front through a cascade of bifurcations.
Nonlinear Electro-Hydrodynamics of Liquid Crystals
Authors: Pikina E. S. , Muratov A. R. , Kats E. I. , Lebedev V. V.
Published: April 2024

We present nonlinear dynamic equations for nematic and smecticAliquid crystals in the presence of an alternating electric field and explain their derivation in detail. The local electric field acting in any liquid-crystalline system is expressed as a sum of external electric field, the fields originating from feedback of liquid crystal order parameter, and a field, created by charged impurities. The system tends to decrease the total electric field, because it lowers the energy density. This basically nonlinear problem is not a pure academic interest. In the realm of liquid crystals and their applications, utilized nowadays modern experimental techniques have progressed to the point where even small deviations from the linear behavior can be observed and measured with a high accuracy. We follow hydrodynamic approach which is the macroscopic description of condensed matter systems in the low frequency and long wavelength limit. Nonlinear hydrodynamic equations are well established to describe simple fluids. Similar approaches (with degrees of freedom related to the broken orientational or translational symmetry included) have been used also for liquid crystals. However to study behavior of strongly perturbed (well above the thresholds of various electro-hydrodynamic instabilities) liquid crystals, the nonlinear equations should include soft electromagnetic degrees of freedom as well. There are many examples of such instabilities, e.g., classical Carr-Helfrich instability triggered by the competitive electric and viscous torques, flexoelectric instability, and so one. Therefore the self-consistent derivation of the complete set of the nonlinear electro-hydrodynamic equations for liquid crystals became an actual task. The aim of our work is to present these equations, which is a mandatory step to handle any nonlinear phenomenon in liquid crystals.
Melting Scenarios of Two-Dimensional Systems: Possibilities of Computer Simulation
Authors: RYZHOV V. N. , Gayduk E. A. , Tareeva E. E. , Fomin Yu. D. , Tsiok E. N.
Published: April 2024

Modern theories of melting of two-dimensional systems are discussed that are mainly based on the concepts of the Berezinskii–Kosterlitz–Thouless (BKT) theory of phase transitions in two-dimensional systems with continuous symmetry. Today there exist three basic scenarios of melting of two-dimensional crystals. First of all, this is the Berezinskii–Kosterlitz–Thouless–Halperin–Nelson–Young (BKTHNY) theory, in which two-dimensional crystals are melted through two BKT-type continuous transitions with an intermediate hexatic phase. In this case a first-order phase transition can also occur. The third scenario has recently been proposed by Bernard and Krauth (BK), in which melting can occur through a BKT-type transition; in this case the hexatic phase–isotropic fluid transition is a first-order transition. The review presents a critical analysis of the approaches used to determine the parameters and the type of transition by computer simulation methods.
Scalable Heteronuclear Architecture of Neutral Atoms Based on EIT
Authors: Faruk A. M. , Beterov I. I. , Pen Syuy , Ryabtsev I. I.
Published: April 2024

Based on our recent paper [arXiv:2206.12176 (2022)], we propose a scalable heteronuclear architecture of parallel implementation of CNOT gates in arrays of alkali-metal neutral atoms for quantum information processing. We considered a scheme where we perform CNOT gates in a parallel manner within the array, while they are performed sequentially between the pairs of neighboring qubits by coherently transporting an array of atoms of one atomic species (ancilla qubits) using an array of mobile optical dipole traps generated by a 2D acousto-optic deflector (AOD). The atoms of the second atomic species (data qubits) are kept in the array of static optical dipole traps generated by spatial light modulator (SLM). The moving ancillas remain in the superposition of their logical ground states without loss of coherence, while their transportation paths avoid overlaps with the spatial positions of data atoms. We numerically optimized the system parameters to achieve the fidelity for parallelly implemented CNOT gates aroundF=95%for the experimentally feasible conditions. Our design can be useful implementation of surface codes for quantum error correction. Renyi entropy and mutual information are also investigated to characterize the gate performance.
A Quantum Algorithm for Solving the Travelling Salesman Problem by Quantum Phase Estimation and Quantum Search
Authors: Tszyun'si Ch. , Beterov I. I.
Published: April 2024

A quantum algorithm for solving the traveling salesman problem by the quantum phase estimation and quantum search method is considered. An approach is developed that was previously proposed for solving this problem. A quantum register is used to encode the eigenstates of a unitary operator whose phase determines the length of each possible route. The quantum phase estimation algorithm is used to estimate the length of a route. Then, to find the minimum route length, the measured values of length are encoded into the states of the second quantum register, and the search for the optimal route is carried out using a modified Grover algorithm. Numerical simulation of the proposed quantum algorithm is carried out using the Qiskit library for one and two iterations of the modified Grover algorithm.
Satellites of the Dipole-Forbidden Transitions to the Low-Lying 2S1/2 and 2D3/2,5/2 Excited States of K, Rb, and Cs Atoms in the Spectra of Gas-Phase Mixtures with CF4
Authors: Alekseev V. A. , Vartanyan T. A. , Pazgalev A. S. , Serdobintsev P. Yu.
Published: April 2024

The luminescence excitation spectra of theD1resonance line of atoms K, Rb, and Cs in gas mixtures with CF4are found to contain satellite transitions, which correspond to the transition of an atom to the states (n– 1)d2D3/2,5/2and (n+ 1)s2S1/2, wheren= 4, 5, and 6 for K, Rb, and Cs, respectively, with the simultaneous excitation of CF4molecule vibrations at the IR active mode frequency ν3with a quantum energy of 1283 cm–1. These satellite transitions are A(ns2S1/2) + CF4(ν3= 0) +hν → A((n– 1)d2D3/2,5/2) + CF4(ν3= 1) and A(ns2S1/2) + CF4(ν3= 0) +hν → A((n+ 1)s2S1/2) + CF4(ν3= 1), where A = K, Rb, and Cs. The appearance of an optical coupling between the upper and lower states of these asymptotically (atRA−CF4→ ∞) forbidden transitions is shown to be caused by the interaction of the dipole moment of the ν3= 1 ↔ ν3= 0 vibrational transition in the CF4molecule with the dipole moments of the electronic transitionsnp2P1/2,3/2↔ (n– 1)d2D3/2,5/2andnp2P1/2,3/2↔ (n+ 1)s2S1/2in an alkali metal atom; as a result of this interaction, the upper state of the satellite transition acquires admixtures of the A(np2P1/2,3/2)CF4(ν3= 0) resonance states.
Coherent Backscattering Peak for Radiation with Low Spatial Coherence
Authors: Kuz'min V. L. , Val'kov A. Yu. , Zhavoronkov Yu. A.
Published: April 2024

The theory is developed and numerical simulation is performed for the coherent backscattering effect in a strongly inhomogeneous random medium with a finite spatial coherence length. It is shown using the Monte Carlo method that the limitation imposed on the number of scattering events corresponds to lowering of incident radiation coherence and leads to angular broadening of the backscattering peak, extending the possibility of using coherent backscattering in biomedical applications. Based on the diagrammatic technique, the modeling of coherent backscattering is developed for the first time beyond the frames of the ladder approximation.
Single Electron Capture in Collisions of Fast Ions with Molecular Hydrogen in the Impact Parameter Representation
Authors: Goryaev F. F.
Published: April 2024

A theoretical method for evaluating the single-electron capture (SEC) cross sections in collisions of fast ions with a ground-state H2molecule is presented. The scattering problem for ion-molecule collisions is formulated in the impact parameter representation using the relation between the quantum-mechanical amplitude and quasi-classical impact parameter one. The capture amplitudes and corresponding probabilities of capture to (nlm) states of an incident ion are derived within the framework of the Brinkman–Kramers approximation. The general expressions for the SEC probability amplitudes ton-states, summed overlandmquantum numbers, are deduced, from which the corresponding SEC probabilities can be then calculated using a procedure of multichannel normalization. The dependence of the differential cross sections, integrated over projectile impact parameters, on the molecular orientation for charge exchange in H++ H2collisions is considered and compared with measurements and other calculations. Total SEC cross sections, integrated over the molecular orientations and summed overn-states for several bare and dressed ions, are calculated and compared with available experimental data and results of calculations by means of other theoretical methods.
On Estimation Methods of Depolarization Losses for Ultracold Neutrons in Magnetic Traps
Authors: Klyushnikov G. N. , Serebrov A. P.
Published: April 2024

The problem of finding the depolarization losses of neutrons is investigated in connection with the need to determine the systematic error for experiments with magnetic storage of ultracold neutrons in traps. In this paper, we consider three methods to estimate the neutrons depolarization probability: classical, quantum mechanical and approximate one. They are used to estimate the depolarization probability of ultracold neutrons in two magnetic traps: the trap developed in Los Alamos National Laboratory (LANL) and the one designed in the neutron physics laboratory of “NRC Kurchatov Institute”—PNPI. It is shown that all three methods are successfully used to estimate depolarization. This is of particular importance to compare of theoretical predictions with the results of measurement in experiments to determine the neutron lifetime.
Periodic Variations of the Radon Concentration Measured by the Large Volume Detector at the Gran Sasso Underground Laboratory
Authors: Agafonova N. Yu. , Dobrynina E. A. , Filimonova N. A. , Shakir'yanova I. R.
Published: April 2024

Time series of gamma-ray photons from natural radioactivity measured with the Large Volume Detector (LVD) at the Gran Sasso underground laboratory (Laboratori Nazionali del Gran Sasso, Italy) have been analyzed. The instrument is used to detect neutrinos from gravitational collapses of stellar cores in the Galaxy. The background of the experiment is due to neutrons and gamma-ray photons from the decays of daughter nuclei of uranium and thorium. An analysis of periodic variations of the number of gamma-ray photons caused by the radon concentration in the underground laboratory has shown the presence of diurnal, weekly, monthly, and annual modulations. Data collected from 2004 to 2021, including a period of low activity in the hall of the Gran Sasso laboratory during the COVID-19 pandemic, have been reported.