An algorithm for calculation of the first and second heart sounds based on an oscillatory model with two degrees of freedom is proposed. The model takes into account elastic parameters of the aortic and pulmonary valves, blood flow in the nearby vessels, and their elastic oscillations. The force acting on the pulmonary valve during its closure was calculated on the basis of pressure differences in the right ventricle and pulmonary artery, which were determined from right heart catheterization data. The calculated heart sound profiles were compared with the measured phonocardiogram signals recorded during catheterization. A good correspondence of signals with optimal choice of valve and vascular parameters was shown. It was found out that the ratio of peaks, frequency and duration of heart tone signals are most sensitive to the value of pressure change rate during valve closure. It is shown that with the help of the developed model it is possible to predict the type of pressure profile in the right ventricle after drug administration for pulmonary hypertension. The results obtained using the algorithm can be used to gain a more detailed understanding of normal and abnormal heart tone generation in humans, and to develop new methods for diagnosing heart disease.
Show AbstractNumerical simulation was carried out for comparative study of iterative and functional-analytical algorithms for solving inverse scattering problem of sound speed and absorption reconstruction. The mathematical properties of these algorithms were previously described in works of R.G. Novikov for the Schrödinger equation. In the present paper, for the case of two-dimensional scalar Helmholtz equation, the efficiency of iterative algorithm in reconstructing medium-strength scatterers and the advantages of functional-analytic approach in reconstructing strong scatterers are demonstrated, which corresponds to the known theoretical estimates of these algorithms’ convergence. To improve the convergence of iterations, a filtering procedure in the space of wave vectors is used, which gradually takes into account the high-frequency components of the spatial spectrum of the scatterer function.
Show AbstractDespite years of research, there are still many open questions about the model of gamma-ray generation by these sources. It is assumed that the measurement of the linear polarization of radiation can provide an answer to a number of unresolved questions in the physics of phenomena. When registering gamma radiation with scintillation detectors, the problem of dead time also arises, during which the device is not able to register a newly received quantum of radiation. It begins to play a significant role when the gamma-ray flux approaches the inverse of the dead time of the detector. Such problems arise when registering terrestrial gamma-ray flashes and the most powerful cosmic gamma-ray bursts. However, by segmenting the detector, it is possible on the one hand to reduce the effect of dead time, and on the other hand to measure the polarization of radiation. In this paper, a simulation of the registration of radiation polarization by a segmented scintillation detector using the Geant4 software package is carried out.
Show AbstractIn this study, we studied the dispersion properties of slow magnetoacoustic (MA) waves propagating in a thermally active plasma. For plasma parameters corresponding to a “warm” coronal loop, the phase velocity of slow MA waves was calculated in the thin flow tube approximation as a function of the wave period for various scenarios of coronal heating. A heating scenario based on observations of decaying slow MA waves in long-lived coronal structures is considered. The presence of a magnetic field in the heating scenario led to the dependence of the modified tube velocity, the new long-wavelength limit of the phase velocity in the presence of thermal misbalance, on the exponent of the magnetic field. Also, a wave scenario of heating was considered, depending on the power index of the frequency spectrum of the emitter, which led to the instability of entropy waves and the stability of MA waves.
Show AbstractIn current work the dependences of the amlitude defect of КДПС-1К detector on mass and energy were determined. Energy calibrations were performed with the 226Ra α-source and calibrational measurement with 20Ne, 36Ar, 86Kr, 132Xe beams were performed at IC-100 cyclotron at FLNR JINR. The research was carried out to measure the effective thickness of "dead layer"of the semiconductor detector and a correction has been made for energy losses in this layer. The expression for estimating corrections for an amplitude defect when measuring reaction products energies the energy range from 20 to 100 MeV and mass from 20 to 132 a.m.u.
Show AbstractThe aim of the paper is measurement of NA62 experiment sensitivity towards the search for forbidden in Standard Model decay $\pi^{0}\rightarrow3\gamma$, that violates C-invariance principle, and allowed in Standard Model decay $\pi^{0}\rightarrow4\gamma$. Current upper limit on the probability of $\pi^{0}\rightarrow3\gamma$ ($\pi^{0}\rightarrow4\gamma$) decay is $3.1\times10^{-8}$ ($2\times10^{-8}$) with $90\%$ confidence level. In the paper $K^{+}\rightarrow\pi^{+}\pi^{0}$ decays are used as a source of $\pi^{0}$. The idea of selection of events with 3 products or 4 products after $\pi^{0}$ decay in NA62 detector was developed. NA62 detector and all physical processes were modelled with Monte Carlo method using Geant4. Single event sensitivity towards $\pi^{0}\rightarrow3\gamma$ ($\pi^{0}\rightarrow4\gamma$) decay without background events consideration is $\mathcal{O}(10^{-9})$, which is 1 order better than current upper limits. Consideration of background events for each decay leads to decline of sensitivity to the level of current limits.
Show AbstractThe main problem considered in this paper is the problem of reprocessing spent nuclear fuel (SNF). The minor actinides, which are the main contributors to the radioactivity of spent nuclear fuel, pose a great danger in the long term. One possible solution to this problem is to burn off the minor actinides by adding them to the fast-neutron reactor fuel. The main object of this study is the core of a fast reactor. The RBEC fast-neutron reactor was chosen as the prototype. The purpose of the work was to investigate the efficiency of using curium as a fraction to fuel the RBEC reactor. In the course of the study, a heterogeneous calculation model of the RBEC reactor core with curium as a fuel fraction was developed, and the neutron-physical characteristics of the core were calculated. These calculations were performed using the "Serpent" software package. As a result of the study, the neutron-physical characteristics of the core with modified fuel were calculated, and a comparison was made with the neutron-physical characteristics obtained for standard uranium-plutonium fuel. Keywords: fast reactor, reactor core, radioactive waste, spent nuclear fuel, minor actinides, curium, transmutation, fractions to the fuel, RBEC.
Show AbstractThe paper presents the results of studying the effect of axial profiling of the burnup absorber in the fuel rods of the fuel assemblies of the VVER-1200 reactor. Profiling was carried out by dividing the fuel rod into 5 equal zones in height, in which the shares of Gd were redistributed, based on data on the distribution of the neutron flux density along the height of the fuel rod of the original model. At the next stage, the concentrations of the remaining isotopes were recalculated so that the total number of nuclei of each isotope in the fuel element remained unchanged before and after the recalculation. Data were obtained on a decrease in the rate of reactivity loss, which allows us to put forward an assertion about the possibility of extending the fuel campaign. An assessment of the change in the conversion ratio was carried out, the influence of profiling on safety was investigated from the standpoint of reactivity effects, the proportion of delayed neutrons. The technology of fuel rod profiling did not have a significant effect on the CR and the proportion of delayed neutrons, the Doppler effect turned out to be almost identical, the density effect of reactivity at the beginning of the fuel campaign turned out to be more negative, at the end less. The accumulation of minor actinides (MA) is considered. The results showed that after profiling, the concentrations of MA increase. This aspect was justified by the calculation of the TVEG cell, which showed that after profiling, the neutron spectrum is warmed by 50%, as a result of which the rates of MA accumulation reactions increase. The data taken in parallel on the energy release in neighboring tablets at the boundaries of the profiling zones showed a significant gradient of energy release closer to the periphery, about 15%. This result requires a safety justification from the position of thermomechanics.
Show AbstractMonte Carlo generator HYDJET++ was used to study the azimuthal anisotropy of particles produced in Xe–Xe collisions at an energy of \sqrt{s_{NN}} = 5.44 TeV and Pb–Pb at an energy of 5.02 TeV per nucleon pair in the center mass frame. Obtained results are compared with the experimental data of the Compact Muon Solenoid (CMS) at the Large Hadron Collider (LHC) in European Council for Nuclear Research (CERN).
Show AbstractA promising alternative to uranium dioxide has been selected and its use for expanding the resource provision of the modern nuclear energy industry has been justified.Thorium-plutonium composite enriched by 7% in plutonium, loaded into fuel elements in the form of tablets, was used as fuel. To achieve the highest productivity, the water-fuel ratio has been changed to 1.2, which allows achieving a record campaign of 1287.5 days. Note that the installation works only in a supercritical state throughout the entire working cycle. The computational studies were performed using the verified calculation code WIMS-D5B (ENDF/B-Ⅶ.0) and modern constant software. The neutron-physical characteristics of the installation were modeled taking into account the changes in the internal structure of the microgranulated fuel caused by the controlled fission reaction and the subsequent migration of fission fragments. When calculating the reactor parameters, the power is assumed to be unchanged, equal to the maximum achievable.
Show AbstractThe paper considers the effect of the addition of americium dioxide to fuel on the neutronics of the fuel assembly of the reactor type VVER-1200 (model V-392M). The simulation was carried out with conditions of radial reflection and axial leakage. The rmultiplication factor, the power peaking factor, the conversion ratio, the proportion of delayed neutrons, and the change in the mass of americium in the fuel were estimated. Calculations were performed in the Serpent 2 software package. Jeff 3.1.1 constant software was used. Statistics of 107 neutron histories were considered. The statistical error of the multiplication coefficient is ~0.02%, the proportion of delayed neutrons is 0.1%, the reproduction coefficient is 0.05%, for uneven energy release and changes in the isotopic composition of the fuel, no assessment was made. The results showed preferential indicators when adding americium oxide to the fuel from the point of view of the evaluation of the reproduction coefficient, the reproduction coefficient. In contrast, the proportion of delayed neutrons worsened. The unevenness of the fuel assembly energy release has not undergone any changes. The neutron spectrum remained identical to the original fuel assembly. As a result, within the simulation, the possibility of burning Am241 in a thermal reactor was confirmed.
Show AbstractWithin the framework of the linear theory of long waves, on the basis of an accurate analytical solution of a one-dimensional problem, the features of the generation of gravitational surface waves during the movement of a non-deformable landslide body are investigated. Explicit expressions describing the energy of the waves, as well as the strength of the wave resistance, are obtained. It is established that the pumping of energy to the waves, and, consequently, the action of the wave resistance force, is limited in time. It is shown that the calculation of the wave resistance force by the instantaneous parameters of the body motion is impossible due to the fact that the magnitude of this force is determined by the prehistory of the movement of the landslide body. Estimates of the magnitude of the wave resistance force suggest that it can be comparable to the forces of "dry" and turbulent friction.
Show AbstractIn this paper, we investigated changes in the filtration properties and internal structure of underground gas storage (UGS) reservoir rocks caused by the impact of an irregular stress field during the implementation of the bottomhole zone permeability increase method - the directional unloading method. The research was conducted with the use of a ProCon X-Ray CT-MINI high-resolution scanner of the Institute for Problems in Mechanics RAS. Multiscale scans of UGS samples with a developed system of macrocracks formed after geomechanical modeling of the process of implementation of the directional unloading method were carried out. 3D structures of the rock interior were obtained, on the basis of which the numerical simulation of the pore and fracture filtration processes was carried out, the granulometric analysis of the matrix and fracture products was performed, and the changes in filtration properties were assessed. The results of the research confirm the effectiveness of the directional unloading method for the conditions of the studied field, allow for the selection of downhole equipment to solve the problems of sand production, and are also intended to extend the existing approaches to the nondestructive analysis of core material of UGS formations and can be used to create and refine the operational model of the UGS.
Show AbstractA numerical method has been used to solve the problem of the Riemann in the case of incomplete opening of the membrane between the regions of high and low gas pressure in a rectangular channel. To verify the numerical model, experiments were carried out to measure the pressure of the gas flow in the shock tube at the TRINITY RF Research Center. The qualitative and quantitative correspondence of the calculated dependencies and experimental data is demonstrated.
Show AbstractThe numerical simulation of adaptive system operation with two sequentially located 18-channel adaptive mirrors with size of 46x56 mm2 in the problem of the phase correction of the laser beam in size of 15x22 mm2 has been carried out. The control of the adaptive mirrors has been realized by the stochastic parallel gradient algorithm. A set of 36 Gaussian functions with a width d=1.73 cm was used to model the response functions of adaptive mirrors. The radiation power within the diffraction angle is the criterion functional of the algorithm. Two variants of system operation have been considered: in the first variant the mirrors have the joint control unit and the criterion functional sensor, and in the second variant each mirror is situated in the independent contour. The similar adaptive systems can be applied to the correction of phase distortions of the radiation caused by strong turbulence of the atmosphere. It is shown, that the efficiency of correction of phase aberrations by such adaptive system is high in the case of the independent contours at supplying on the first adaptive mirror relatively small stochastic voltages. The mutual influence of adaptive mirrors on each other's work during correction is investigated.
Show AbstractBy ab initio modeling method for the lattices of ices Ih, III, and lattices of hydrates sI, sH the densities of electronic states were obtained, electronic εel and ionic εion contributions to the static dielectric tensor were calculated. Ices Ih, III and hydrate sH show a dedicated axis of the dielectric tensor εel, and hydrate sI demonstrates isotropy of εel. The inclusion of Xe and CH4 in the sI hydrate stabilizes the lattice and increases the values of the dielectric tensors εel and εion, due to increased polarizability. The study of the dielectric functions ε'(ω) and ε"(ω) shows the presence of active absorption at energies of 5 ÷ 20 eV, and an optical gap EOG ≈ 5 eV.
Show AbstractThe article presents the results of finite element modeling of a pyroelectric accelerator based on a single crystal of lithium tantalate. The influence of the charge distribution on the crystal surface on the characteristics of the electron flow is considered. A model using an axially symmetric charge distribution obtained by interpolating the experimental dependence leads to the expected effects of self-focusing and monoenergicity of the flow. Attention is also paid to the model "triangular"\; distribution. This distribution can be caused by the structure of the lithium tantalate domain walls when its temperature changes. Simulation results for both distributions are discussed.
Show AbstractThe paper presents a method for decomposing a signal into components of a known shape in the form of N- and U-waves obtained by partial reflection of infrasound from thin inhomogeneous layers of the atmosphere. A mathematical model of the signal is proposed as the sum of incoming waves with different amplitudes and phases, as well as random noise. The completeness of the system of functions consisting of such waves is shown. The method allows to separate components of a known shape from the signal and determine their parameters. The proposed method can be used to search for components of arbitrary shape in the signal.
Show AbstractThe paper evaluates the structural, electrophysical and mechanical properties of IV-B dioxides and the HfxA1-xO2 compound (A = Zr, Ti) by the density functional theory method in the Quantum ESPRESSO software package. It is established that orthorhombic TiO2 titanium dioxide does not exhibit ferroelectric properties, has a narrow band gap and a high value of dielectric permittivity compared with orthorhombic hafnium and zirconium dioxides. The introduction of zirconium atoms into the hafnium dioxide unit cell does not cause significant changes in the structure, leads to a decrease in the band gap and an increase in residual polarization. Compounds of the type HfxZr1-xO2 (x = 0.25, 0.5) have a high value of the elastic modulus, compared with stoichiometric HfO2 and ZrO2.
Show AbstractThis paper investigates the construction of an intelligent system for planning the trajectory of a mobile robot in an environment with obstacles. To solve this problem, the authors propose to use a modified particle swarm optimization (PSO) algorithm. The modification involves three aspects. The first aspect introduces two parameters as detectors to find a particle that cannot improve its personal optimum and global optimum in a predetermined number of successive iterations, and replaces it with a rebuilt one. The second changes the velocity constraint and thus increases the diversity of the population. The third introduces a variable parameter ω, which balances the global and local search abilities. This modification increases the diversity of the population by balancing the global and local search capabilities, and avoids stagnation and local optimization problems without losing the fast convergence property of PSO. Modeling and analysis of the obtained data allow us to conclude that the proposed modified PSO algorithm is effective for planning the trajectory of a mobile robot in an environment with obstacles.
Show AbstractThe paper proposes a mathematical model of silver nanoparticles biokinetics in an organism of laboratory mice using the concept of physiologically based pharmacokinetic modeling and previously obtained by high-precision method of instrumental neutron activation analysis of the experimental data. Analytical and numerical solutions for this model were calculated. The applicability of different assumptions is considered and justified. The obtained solutions were analyzed and the biokinetic constants of transition rates, plateau times, mass contents of stable equilibrium were calculated. Numerical parameters have been compared with previously obtained parameters in another paper on the biokinetics of silver nanoparticles of the same brand. It is concluded that the proposed approach is well applicable to the modeling of silver nanoparticles biokinetics in a living organism.
Show AbstractThe article is devoted to the study of the effect of a two-micron fiber laser on biological tissue. The paper describes the results of experiments conducted using continuous and ultrashort pulse laser radiation with energies from 1.5 to 20 J in a spectral range of 2 microns on biological tissue. Experimental dependences of the depth and diameter of the impact zone on energy were obtained, and it was also found that the diameter and depth of the ablation and coagulation zone are fixed at an impact energy of ∼10 J in the pulsed mode. In general, the results of the work can be used to optimize procedures for the treatment of biological tissue using laser exposure.
Show AbstractThis article substantiates in detail the need to expand the use of esCCO technology in order to determine the state of human health, especially when he is in critical condition or close to it. In such situations, getting information about cardiac output quickly and accurately is an important factor for doctors to make decisions and ensure optimal medical care. The advantage of esCCO technology is its ability to provide the necessary information in a shorter period of time than using other methods. This allows doctors to quickly assess changes in cardiac output and take appropriate measures to normalize the patient's condition. The article also discusses the features of using esCCO technology to determine the state of human health in various situations where changes in cardiac output play a key role. Examples of recording various parameters necessary for calculating cardiac output using the esCCO method were presented, as well as experimental data demonstrating changes in cardiac output over time. Expanding the use of esCCO technology in medical practice is an important step in the development of modern medicine aimed at improving the efficiency and quality of medical care.
Show AbstractDue to the complexity of the chemical and molecular composition of oil, it is usually used to identify four main components: asphaltenes, resins, paraffins and oils. According to the accepted methods of GOST 11851085, M 01-12-81 paraffins are extracted not directly from oil as, for example, asphaltenes, but from pre-separated oils. In this study, results of research by NMR of benzene and alcohol-benzene resins extracted from oil according to the standardized procedure of GOST 11858-66 were carried out. It was found that benzene resins show hysteresis in NMR characteristics that is typical of systems with the first order phase transition, while alcoholtobenzene resins show no hysteresis over the temperature range from minus 80 to plus 65 degrees Celsius accurate to the experimental error. It has been suggested that as a result of peculiarities of interaction between resins and paraffins, the paraffins are extracted from oil mainly in the composition of benzene resins.
Show AbstractThis paper considers a broad-area surface-emitting laser with a vertical resonator (VCSEL) controlled by external optical radiation, which provides the presence of optical bistability in the system. The stability of the spatially homogeneous near-axis mode of laser generation is investigated. Interaction of a large number of transverse modes leads to modulation instability, as a result of which spatial patterns, solitons and irregular dynamics can be formed. Conditions for the existence of bistable modes on the background of modulation instability are investigated. A curve of a homogeneous stationary solution is constructed and the correlation between its bistability and the presence of instabilities is shown. The system of differential equations was solved numerically to confirm the effect of switching between the stationary values in the bistable region. It is obtained that the growth of the Henry factor value increases the areas of modulation instability and plane wave instability, which can also be realized in this system.
Show AbstractThe paper shows the possibility of using convolutional neural networks for a laser beam wavefront reconstruction by measuring the intensity distribution in the transverse plane at some distance behind the focusing system. The optimal distance from the focusing system to the measurement plane is determined at which the error for the rms devation of Zernike polynomials amplitudes decreases sharply. A neural network has been trained on a computer-generated samples of beams with various types of aberrations to reconstruct the wavefront of real beams in the presence of noise
Show AbstractThe creation of highly efficient semiconductor lasers in the spectral range 1300-1550 nm is one of the important practical problems of modern quantum electronics. The leading direction in the use of such lasers is the transmission of information over an optical fiber. The improvement of these devices requires an increase in the output power, the level of which for lasers in the considered spectral range is largely determined by the design of the quantum-well active region. In particular, the introduction of elastic stresses into quantum wells of the active region helps to reduce the intensity of the Auger recombination processes and favors an increase in the output power and temperature stability. This work is aimed at finding ways to create quantum wells with an increased level of elastic stresses emitting in the region of 1300-1550 nm. The article takes into account the effect of elastic stresses on the radiation wavelength, calculates the geometry of quantum wells that provide the emission wavelength of 1300-1550 nm, determines the critical thickness of such quantum wells, above which the generation of misfit dislocations begins. Approaches for compensating elastic stresses in quantum wells have also been studied, and it has been shown that the use of barrier layers with elastic stresses of the opposite sign makes it possible to push back the generation threshold of misfit dislocations and improve the radiative efficiency.
Show AbstractIn this study, the need to develop a compact mobile high-resolution digital microscope for the research is substantiated. Disadvantages of modern mobile digital microscopes designs are considered. The requirements for providing the necessary characteristics in a compact microscope in terms of resolution, image contrast and size are determined. The design of the low-cost compact mobile digital microscope is developed and assembled. The condition to ensure necessary magnification is introduced. According to this condition, various parameters of the microscope are evaluated and compared with laboratory microscopes parameters. The results of studies of different objects are presented with the resolution from 2 μm to 90 nm.
Show AbstractThe features of the implementation of the educational module on statistical optics are considered, taking into account the development of new scientific areas, special attention is paid to the urgent task of updating and expanding methodological materials devoted to the study of speckle structures with Rayleigh and non-Rayleigh statistics. A description is given of a new problem in a special optical workshop created for the experimental study of the properties of speckle-like light fields.
Show AbstractThe problems that arise during the express control of hydrocarbon media and their mixtures are considered. Especially noted the problems with the control of volatile hydrocarbon media that are used as fuel (gasoline, kerosene, diesel fuel, etc.). The requirements to the methods for express control and devices for their implementation are defined. The features of control of volatile hydrocarbon media and their mixtures using small-size refractometers working on the effect of total internal reflection are considered. It is shown that when using these devices, it is impossible to obtain data to determine the state of the mixture of volatile hydrocarbon media, its composition and the concentration of the components. A new method for determining the components in the mixture of volatile hydrocarbon media and data on the ratio between the concentrations of the components in it has been developed. The design of a small-size refractometer, which makes it possible to measure the refractive index in visible light, for the implementation of this method is presented. The dependences of the density change on the temperature T for different grades of gasoline for determining the composition and concentration in a three-component mixture of volatile hydrocarbon media have been established. The results of studies of various volatile hydrocarbon media and their mixtures are presented.
Show AbstractThe article grounds a necessity of liquid media control using refractometer. A method for monitoring liquid media, including mixtures, using refractometric measurements is proposed. A system of equations has been developed to determine the composition of the medium, which consists of components that have not reacted chemically. The results of experimental studies are presented.
Show AbstractThe article analyzes the main malfunctions of cars that occur during operation on the North-Western Railways. Faulty wheelset treads were identified as one of the major problems in the early stages of car repairs. An overview of modern methods for measuring surfaces using laser technology is presented. The article discusses the principles of operation of laser profilometers, their main components, as well as methods for processing the obtained data. The application of laser profilometers in various fields such as industry, construction, medicine and science are described. The advantages and disadvantages of laser profilometers compared to other surface measurement methods are also discussed. To reduce the stopping time of passing trains, it is proposed to introduce laser profilers on the railway tracks. As a template is applied to a real wheel for measurements during the technical inspection of a rolling stock car, so in the proposed method, measurements are made at points according to the template. The technical result is an increase in the accuracy of measurements by minimizing the human factor, global digitalization of technological processes and automation of rolling stock control along the route. In the course of the work, data obtained from measurements of various profiles of the surfaces of freight cars, including wheelsets, were analyzed in comparison with reference profiles.
Show AbstractThe terahertz (THz) frequency range in the electromagnetic radiation spectrum occupies an intermediate position between the infrared and microwave ranges and the radiation within it has the properties of both, i.e. it has a low divergence and is able to penetrate through non-metallic materials. Currently, the existing THz radiation receivers are inert, have low spatial resolution and high cost, which raises the question of finding suitable affordable analogues. The solution may be the use of matrix photodetectors based on charge-coupled structures (CCD) and metal-oxide-semiconductor (CMOS) structures operating in the mode of tunneling photoelectrons into the conduction band due to an external laser source. The paper considers the features of registration of modulated electromagnetic radiation in the extended millimeter and submillimeter wavelength ranges using CCD and CMOS matrices.
Show AbstractPolar liquid crystal mesophases are of great interest from both fundamental and applied perspectives. Ferrielectric liquid crystals encompass various polar mesophases, the common drawback of which is the narrow temperature range of existence (within 10 °C) and high melting temperatures (above 60 °C). This paper presents a ferroelectric liquid crystal mixture with a mesophase existence range from -3 °C to +47 °C. It is shown that this mixture is currently the lowest-voltage quadratic liquid crystal electro-optic medium, with a Kerr orientation effect coefficient reaching 1500 nm/V2. Thus, based on the presented mixture, it is possible to create electro-optically controllable half-wave plates with a control voltage of approximately 1.3 V and electro-optic response times of 150 μs.
Show AbstractThe dependences of the photoluminescence of two types of carbon dots synthesized by the hydrothermal method and the Hummers method on the characteristics of various solvents were achieved. As a result of the analysis of the obtained photoluminescence spectra of suspensions of both types of carbon dots in all used solvents, a significant effect of the acidity, basicity, and relative polarity of the solvent on the intensity and Stokes shift of the photoluminescence of carbon dots was revealed. The results obtained are explained by the processes of change in the chemical and electrical properties of carbon dots when interacting with media with different physicochemical characteristics.
Show AbstractThe results of an experimental study of the effect of gold and silver nanoparticles (NPs) on the optical absorption and luminescence of erythrosine molecules in a polyvinyl alcohol (PVA) film are presented. It is shown that the presence of plasmonic NPs leads to an increase of the light absorption by molecules, a reduction of the phosphorescence lifetime and a non-monotonic change of the fluorescence and phosphorescence intensity of molecules depending on the concentration of NPs. As the NPs concentration increases, an increase of the lumines-cence intensity is first observed, which after reaching the maximum is replaced by a decrease.
Show AbstractThe article is devoted to the study of the formation of apodized laser beams by jagged diaphragms. The formation of beams by square and rectangular diaphragms with different types of jagged structure is considered. The possibility of forming apodized beams with a filling factor of up to 87% and a peak to average energy density ratio of less than 1% is shown. The preservation of the spatial structure of the formed beams during their propagation from the plane of rebuilding the image of the toothed diaphragm is studied. The possibility of using toothed rectangular diaphragms in the system of aperture division of a laser beam is shown.
Show AbstractThe necessity of developing optical systems for adjusting the position of the laser radiation axis on a photodetector module for an aerial fiber-optic communication line is substantiated. The design of an optical system for adjusting the axis of laser radiation on a photodetector module in a plane perpendicular to the laser radiation has been developed. The operation of an optical system for controlling the position of the laser radiation axis on the photosensitive layer of the photodetector is simulated. The optimal parameters of the system components are determined and control methods are proposed that allow achieving the necessary accuracy and stability of the radiation direction. Experimental studies aimed at correcting the position of the plates relative to the direction of the axis of laser radiation and changing their refractive index by changing the voltage are presented. The efficiency of the developed optical system is confirmed and the optimal parameters of its optical elements are determined.
Show AbstractIn this work, the methods of Raman spectroscopy, dynamic light scattering (DLS), and absorption spectroscopy in the ultraviolet region were used to study aqueous solutions in which the synthesis of ZnS nanoparticles was carried out by co-precipitation. It was found that more than 99% of the synthesized nanoparticles were 41 ± 3 nm in size, and aqueous suspensions of ZnS nanoparticles had an absorption band in the region of 315 nm. As a result of studying the processes in the reaction medium by Raman spectroscopy, it was found that the band of stretching vibrations of HS - ions in the region with a maximum of 2572 cm-1 is an identification sign of the synthesis of nanoparticles: it is possible to determine the stage and completion of the synthesis of ZnS nanoparticles by its intensity. The results obtained make it possible to develop a non-contact and express method for diagnosing the reaction medium during the synthesis of nanoparticles in them.
Show AbstractThe necessity of increasing the metrological characteristics of the quantum frequency standard on rubium-87 atoms is substantiated. It is noted that the main destabilizing factor that reduces the accuracy of frequency determination is temperature. To control it in the quantum frequency standard, thermostating and thermoregulation are used. It is established that the currently used systems for laser and optical components cannot provide the necessary temperature stability, which is required to improve the metrological characteristics of the quantum standard. A new circuit of a quantum frequency standard temperature controller with a rubidium gas cell using a PID controller has been developed, and its operation in the Micro-Cap environment has been simulated. Transient processes in the circuit of the thermostat are analyzed. A decrease in the influence of temperature on the optical components and characteristics of the laser in the quantum frequency standard was found.
Show AbstractThe magnetoresistance mechanisms of Bi$_{1.1-x}$Sn$_x$Sb$_{0.9}$Te$_2$S (x = 0.02 and 0.04) topological insulators were investigated. The studied crystals have suppressed bulk conductivity, which al-lows us to study the low temperature effects that occur in the surface conducting states. In the measurements by four-probe DC resistance measurements the quantum correction improving conductivity in low fields (H > 1 kOe) was detected. This quantum correction corresponds to the case of weak antilocalization. The parameter of the phase coherence length 𝑙ϕ was extracted and its temperature dependence was determined. It was found that an external magnetic field (H > 1 kOe) activation gap appears in the energy spectrum of surface current carriers in Bi$_{1.1-x}$Sn$_x$Sb$_{0.9}$Te$_2$S (x = 0.02 and 0.04) TI. The energy of the activation gap was estimated and its dependence on the stannum concentration and the applied magnetic field was determined: 𝛥 of the order of 2 meV for Bi$_{1.06}$Sn$_{0.04}$Sb$_{0.9}$Te$_2$S and 60 μeV for Bi$_{1.08}$Sn$_{0.02}$Sb$_{0.9}$Te$_2$S at H = 5 kOe.
Show AbstractAnalytical description of the effects occurring in the chain of Josephson junctions experimentally investigated in [1] within the resistive model for each of the junctions requires a complete analysis of the dynamics of the solitary contact under the action of the current source. We present the results of the bifurcation analysis of the above system in the region of large effective transition resistance, including the description of the circumstances of the heteroclinic loop failure. A diagram of the macroscopic dynamics modes of the solitary transition is obtained. Asymptotic decompositions in time and phase harmonics are constructed. The results of the analysis of peculiarities and sources of irregularity of the expansion by temporal harmonics are outlined, including specification of the type of peculiarities.
Show AbstractIn this work, we study the change in the electrical characteristics of LED structures based on InGaN/GaN, caused by the flow of a large current in a pulsed mode. Stable switching between high-conductivity (resistive) and low-conductivity (diode) states, accompanied by a change in the current transfer mechanism, is found. The movement of mobile defects and the formation of conducting filaments (channels) in the space charge region are considered as the main switching mechanism.
Show AbstractRecently, self-organizing networks of nanoparticles and nanowires have shown promise as systems for neuromorphic reservoir computing. The advantages of such systems are high energy efficiency, absence of necessity for connections between elements within networks, scalability, availability of synthesis technologies, etc. In this work, we calculate the conductance of tunneling contacts between nanoparticles and study the molecular dynamics of the destruction of filamentous compounds. Experimental studies of a percolation memristive network of silver nanoparticles are presented. Using cyclic voltammetry, switching between the capacitive and memristive states of the network is demonstrated and its features are considered.
Show AbstractIn this work, the photoelectric properties of Co3O4/Zn composites with different contents of zinc atoms in the range from 0 to 33 mole percent by cation (mol%) were studied. The composites were obtained by electrospinning and consisted of nanofibers 150–200 nm in diameter with a nanocrystalline structure. The possibility of increasing the dark conductivity and photoconductivity of Co3O4/Zn composites by adding zinc atoms to the structure has been demonstrated. It has been found that the kinetics of the rise and fall of photoconductivity when samples are illuminated with ultraviolet radiation can be approximated by the sum of two exponentials. This indicates the existence of two different processes that determine the recombination of nonequilibrium charge carriers in the material. It is shown that one of these processes can be associated with the adsorption and desorption of molecules on the surface of nanofibers. The ability to carry out adsorption and desorption due to illumination of Co3O4/Zn composites makes them promising for use in gas sensors.
Show AbstractWe present an overview of the recently obtained results for prospects for light dark matter search in experiments at the future Super c-tau factory in models of a leptophilic scalar and a dark photon. The collider sensitivity curves at the 90 % C.L. in the mass range of mediators up to several GeV demonstrate the power of the future electron-positron collider for dark matter manifestations' search. A self-consistent dark matter model containing an additional scalar and a massive vector is proposed, and exact terms for the interactions between additional bosons and fermionic fields of the Standard Model are obtained.The limiting case of small mixing and small masses of the dark vector is considered.
Show AbstractWithin the framework of the perturbative quantum field-theoretical approach with the distance-dependent propagator, neutrino oscillations in matter are considered. In the approximation of two neutrino flavors, the distance-dependent propagator is constructed that describes the propagation of neutrinos in a stationary non-polarized homogeneous medium. Using this propagator, the corresponding probability of the neutrino oscillation process is found, where the neutrinos are detected through the weak charged- and neutral-current interactions. It is shown that the results coincide with those obtained in the framework of the standard quantum-mechanical description. Several specific examples of processes are considered and the MSW effect is discussed.
Show AbstractRecently, the LHCb collaboration established an upper experimental limit on the branching fraction of the rare radiative decay of the Ξ−b baryon: Br(Ξ−b → Ξ− γ)< 1.3x10^{-4}. The measured value is below the branching fraction predicted within the light-cone sum rules. In this paper, the process Ξ−b → Ξ− γ is investigated in the framework of the relativistic quark model, based on the quasi-potential approach in quantum field theory. Form factors are calculated with the consistent consideration of the relativistic effects. The obtained result for the decay branching fraction is below the upper experimental limit set by the LHCb, and is also consistent with some other theoretical calculations within error bars.
Show AbstractMasses of the ground and excited states of fully heavy tetraquarks with open charm and/or bottom are calculated on the basis of the relativistic diquark-antidiquark picture of tetraquarks. In the framework of the quasipotential approach the relativistic potential of the diquark-antidiquark interaction is constructed with the account of both spin-dependent and spin-independent contributions. It is shown, that in the considered asymmetric in composition systems, there is a significant mixing of states of tetraquarks with the same quantum numbers, but different full spins of the tetraquark. The predicted values of the masses of such tetraquarks are compared with the decay thresholds for a pair of heavy mesons. The possibility of experimental observation of such tetraquarks is discussed.
Show AbstractSemileptonic decays of $D$- and $D_s$-mesons into orbitally excited states of strange and light mesons are studied in detail within the framework of the relativistic quark model based on the quasipotential approach and quantum chromodynamics. The form factors that parameterize the matrix elements of the weak current between meson states are calculated with consistent allowance for relativistic effects. Their dependence on the square of the transferred momentum is explicitly defined throughout the accessible kinematic region. Using the helical amplitude method, differential decay widths, branching fraction, various asymmetries and polarization characteristics, which can be measured experimentally, are calculated. The results obtained are in good agreement with the available experimental data.
Show AbstractThe Higgs sector of minimal supersymmetry with explicitly CP violation is considered under the assumption that the lightest neutral Higgs boson without definite CP parity is associated with the observed scalar. The analysis of the alignment limit leads to two possibilities for its realization: 1) the condition $\beta-\alpha \simeq \pi/2$ , known in the CP-conserving limit, is supplemented by $c_1 \simeq 0$, $k_1 \xi_1^{I} =1$; 2) the masses of the Higgs bosons are not decoupled and of the order of the electroweak scale, and $m_H^2 \simeq m_{h_1}^2$, $c_2 \simeq -c_1 \tg (\beta - \alpha)$, $k_1 \xi^{\rm II}_1 \xi^{\rm II}_2 \xi^{\rm II}_3 =1$. CP-violating effects in the alignment limit and the values of CP mixing angle $\alpha_{\rm cp}$ are discussed.
Show AbstractRare Higgs boson decays into a quarkonium-pair are theoretically investigated. The main production mechanisms have been studied in detail as well as their interference within the Standard Model. The one-loop corrections to the decay widths have been taken into account. Such research is potentially of interest in terms of Higgs boson decay modes observation on future facilities.
Show AbstractIn this work, a theoretical study of the ponderomotive magnetic force of interaction between two halves of a long rod cylindrical magnet, uniformly magnetized perpendicular to the cylinder axis, depending on the influence of the magnetic field of two other similar magnets arranged symmetrically, is carried out. It is shown that the bonding force of these halves depends significantly on the configuration and arrangement of the magnets.
Show AbstractThe temperature behaviour of the energy quantities --- kinetic energy and potential energy components --- is studied in the temperature range below 0.25 eV in the semimetal phase of the extended Hubbard model. It has been established that the collective properties of electronic excitations exhibit various features and depend on temperature. The quantities of energy and order parameters are used for the analysis. The technical difficulties of modeling are mentioned as well as the ways to overcome them.
Show AbstractWe consider diffraction radiation (ODR) arising from the uniform and rectilinear motion of an electron near three interacting nanoparticles. It is shown that as a result of the interaction, the characteristics of radiation from such a system change significantly. The calculation in the dipole approximation of the electric field strength, as well as the spectral-angular distribution of the ODR energy, was carried out. The calculated spectral and angular characteristics of radiation are analyzed. Conditions are obtained under which the interaction significantly affects the radiation efficiency. These results are compared with the results obtained by introducing the effective polarizability of a cluster of particles. The possibility of calculating the radiation field for an arbitrary number of interacting nanoparticles is shown. An algorithm for generalizing the problem to a large number of nanoparticles is proposed.
Show AbstractThe measurement process in the deterministic de Broglie-Bohm theory is investigated. The simplest devices for measuring coordinates and momentum are modeled, while both the measurement device and the quantum system are described by the same unified laws. Thus, the problem with the probability distribution in the momentum space, posed in the works \cite{kurt,naun,heim}, is solved. The trajectories of de Broglie particles are calculated numerically. The restoration of the Heisenberg uncertainty principle is qualitatively verified when the coordinate and momentum are measured alternately.
Show AbstractThe $SU(2)_L \times U(1)$ gauge model with an extended lepton sector by three right-handed Majorana sterile neutrinos is considered. Diagonalization of the full $6\times6$ mass matrix of active and sterile neutrinos was carried out. There are two main scenarios that do not contradict cosmological restrictions on sterile dark matter neutrinos: <<exponential mixing>>, in which complex-valued parameters of the mixing matrix can amplify its components by several orders of magnitude, and <<minimal mixing>>, in which there are only masses and mixing parameters of active neutrinos, as well as masses of sterile neutrinos. Two heavy sterile neutrinos with quasi-degenerate masses up to 5 GeV can induce the deviation of lepton universality violation parameter in the decays of $pi^+$ and $K^+$ mesons from the the Standard Model value. Contours are obtained for the permissible values of this parameter within the framework of two mixing scenarios, taking into account the lifetime boundary for heavy neutral lepton from Big Bang nucleosynthesis in the Universe. When calculating the decay width of heavy neutral leptons in the framework of the model with six Majorana neutrinos, three active and three heavy, both two-particle and three-particle lepton decays, essential for masses below the mass of the pion, were taken into account. For the second scenario, a mass region of $460 \text{~MeV} <M< 485$ MeV has been found that allows violation of lepton universality in charged kaon decays at the level observed in the experiment.
Show AbstractMultiple magnetic and kinetic solar wind plasma parameters are used to detect coronal mass ejections (CMEs) as they travel through the heliosphere. There are various interplanetary CME (ICME) catalogues, but due to differences between their ICME identification criteria they can significantly vary. In this paper we analyze Richardson & Cane and CMC CME Scoreboard ICME catalogues and the SRI RAS solar wind types catalogue, and propose an algorith of merging them. A unified catalogue is constructed for 2010 to 2022. The resulting catalogue is completed with data from the OMNI database. Analysis of the unified catalogue demonstrated high accuracy when merging events present in multiple catalogues and a tendency of events defined in all three initial catalogues to demonstrate greater duration, speed and geoeffectiveness. The catalogue is presented on SINP MSU’s Space Weather Exchange website: https://swx.sinp.msu.ru/tools/icme_list.php.
Show AbstractSmall Imaging Telescope (SIT) is a part of the TAIGA astrophysical complex located in the Tunka Valley (Republic of Buryatia, Russia), 50 km from Lake Baikal. The main feature of this prototype is the use of silicon photomultipliers (SiPM) as the sensitive element of the detection camera. This paper presents the results of the calibration procedure of the prototype camera in the context of the the dependence between "the number of photoelectrons and the number of ADC readings" at different temperatures and voltage values for individual SiPMs. The calibration was done using the data obtained by the telescope.
Show AbstractThe TAIGA Astrophysical complex (Tunka Advanced Instrument for cosmic ray and Gamma Astronomy) is located in the Tunka Valley at a distance of 50 km from Lake Baikal and is designed to solve problems of gamma astronomy and high-energy cosmic ray physics. The combined operation (hybrid approach) of atmospheric Cherenkov telescopes of the TAIGA-IACT (Imaging Atmospheric Cherenkov Telescope) and wide-angle Cherenkov detectors of the TAIGA-HiSCORE (High Sensitivity COsmic Rays and gamma Explorer) installation is aimed at registering gamma quanta with energies of more than 40 TeV. According to the data of the TAIGA-HiSCORE installation, information about the direction of arrival of the SHAL and the energy of the primary particle is restored by means of amplitude-time analysis. According to the TAIGA-IACT installation, events from gamma quanta from the hadron background are distinguished with high accuracy by analyzing the image obtained in the telescope camera from the Cherenkov light. The paper describes a technique for reconstructing the parameters of extensive air showers (EAS) induced by high-energy gamma quanta, the results of processing experimental data from the observation of the Crab Nebula source (for 3 seasons in the period 2019-2022, more than 150 hours of observations) obtained by the hybrid method.
Show AbstractA method for restoring the high energy cosmic rays mass composition (1-100 PeV) based on attribution mass for each shower event using the SPHERE-2 Cherenkov radiation detector is presented. To estimate the errors in determining the mass, the simulated events of extensive air showers Cherenkov light without taking into account the background of the night sky was used. To simulate artificial events, various models of the nucleus-nucleus interaction are used, the predictions of which can differ markedly. The mass restoring procedure is based on two models of hadronic interaction, which are very different from each other in the energy range of 1–100 PeV. These are the QGSJET-01 and QGSJETII-04 models. Thus, the independence of data processing from the choice of the nuclear interaction model is ensured. The developed method for restoring the mass composition can be applied to any experiment of the SPHERE type.
Show AbstractThe article is concerned to the inverse problem solution of the propagation of galactic cosmic rays (GCR) from a close source (supernova) to an observer by means of constructing a model of cosmic ray transport with an anisotropic diffusion tensor. A model of the contribution of a point source to the background spectrum of cosmic rays is considered, the best fit for the approximation of the observed proton spectra according to the data of NUCLEON, CALET and PAMELA is carried out. According to the estimated distances, a possible interpretation of the CR (cosmic ray) knee in the region of 10 TeV is presented. An assumption is made about possible candidates causing a change in the observed spectrum.
Show AbstractReconstruction of the direction of arrival of a high atmospheric atmosphere (EAS) is one of the goals of the SPHERE experiment. A new method is presented for the recovery of direction, it compares the time delays of photons in the PMT, transferred to the snow, with the model delays of the curved front of the EAS CR. The analyzed events are initiated by nuclei (H, N, Fe) arriving at zenith (10º, 15º, 20º) and azimuth angles (0-360º) with primary energies of 10 PeV and 30 PeV. This method gives average errors of about 3º for primary energies of 10 PeV at 500 m and 900 m, and about 2º for 30 PeV on average for two heights.
Show AbstractSmall Imaging Telescope (SIT) - a prototype of a wide-angle telescope with an aperture of about 0.1~m$^2$, equipped with a SiPM matrix, which has a number of advantages over PMTs. This paper presents the data analysis for this telescope, which operates in conjunction with the HiSCORE complex. Events for the years 2019–2022 were analyzed. A total of about 7 million trigger frames were analyzed, among which about 5~million EAS events were detected. The analysis was carried out in several steps: initial tuning of the frames using a synchro pulse, search for events and their cleaning according to the method given in the work.
Show AbstractGalactic cosmic rays play an important role in cosmic physics. Despite numerous studies in the field of the magnetic fields of the Galaxy, the understanding of the structure of magnetic lines remains insufficient for predicting the trajectories of high-energy cosmic particles in various configurations of galactic magnetic fields. In this work, the magnetic field is studied numerically by constructing its two-component model and its further qualitative and statistical analysis. At a qualitative level, the results of modeling a random isotropic field, where the magnetic lines are located close to each other, are presented. In this case, a regular structure is observed (see Section 2.2). It is shown that when simulating an isotropic random field, a diffusion mode of motion is observed. When a regular component of a certain intensity is added, the longitudinal mode of transport becomes ballistic.
Show AbstractIn the PAMELA experiment, the anomalous effect of increasing the positron fraction in the total electron-positron flux of galactic cosmic rays at energies above ~ 10 GeV was found for the first time. In the AMS-02 experiment, the positron flux was extended to the TeV region of energies. These measurements confirmed the unusual positron spectrum behavior at high energies. At the moment, various theories of production and acceleration of positrons to such energies are actively discussed. To test these theoretical models, independent measurements of positron and electron fluxes at energies ~ 1 TeV and above are necessary. In the present work we studied the applicability of the technique for detecting positrons and electrons in the TeV energy range by means of their synchrotron radiation in the Earth's magnetic field. We simulated the detection of positrons and electrons using this technique at different orbits and latitudes. It was shown that polar regions provide greater detection efficiency. Based on current data on the total electron-positron flux of cosmic rays in the TeV energy range, it was obtained that the high-latitude orbit of the planned Russian Orbital Service Station provides greater statistics than that of the International Space Station. The calibration dependences allowing to reconstruct the energies of charged particles from their synchrotron photon registration are analyzed.
Show AbstractThe structure and temperature stability of the magnetic properties of the Gd0.81Zr0.19(Co0.7Cu0.1Fe0.2)5.16 alloys after various heat treatment are investigated. It is shown that the heat treatment regimes determine the parameters of the nanostructure and the temperature stability of the magnetic properties of the alloys. The AFM studies of the surface of the Gd0.81Zr0.19(Co0.7Cu0.1Fe0.2)5.16 alloy samples showed that a cellular nanostructure is formed after annealing at 800°C, while the nanostructure parameter (cell size) of quenched and slowly cooled samples differ by 50%. The temperature specific magnetization studies show that the hysteresis characteristics (remanence magnetization and coercive force) of the alloys have temperature stability up to 500 K (227°C). It was found that thermal cycling of the Gd0.81Zr0.19(Co0.7Cu0.1Fe0.2)5.16 alloy in the range from 300 to 600 K (27–327°C) does not lead to changes in its magnetic properties at room temperatures. The second full heat treatment of the destructured sample after heating up to 1000 K (727°C), leads to a partial recovery of hysteresis properties, a change in the phase components of the alloy, and the destruction of the order of the nanostructure.
Show AbstractThe development of nanotechnologies give rise to the nanoelectromechanical devices, in which mechanical movements are induced and detected electrically. Many antiferromagnetics are characterized by a magnetoelectric effect, so it seems interesting to investigate how pronounced magnetomechanical effects are in magnetoelectric films, micro and nano-particles. In this paper, the possibility of the existence of an electrically induced magnetomechanical effect in antiferromagnetics is investigated, its evaluation for samples of different geometries is made, and methods for recording and enhancing the effect, including the detection of the resonance effect using a probe microscope, are discussed.
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