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Abstract: Ni@C nanocomposites in a graphite-like carbon matrix and cobalt nanoparticles in carbon nanotubes were obtained by solid-phase pyrolysis of nickel phthalocyanine (NiC32N8H16) and cobalt phthalocyanine (CoC32N8H16). The metal concentrations in the carbon matrix in both cases in Ni/C and Co/C are the same—12 wt %. The structure and morphology of the obtained samples were studied by high-resolution scanning and transmission electron microscopy as well as X-ray diffraction. The capacitive and resistive characteristics of the obtained Ni/C and Co/C compounds as an electrode material for supercapacitors (SC) have been investigated. The specific capacitances measured by cyclic voltammetry are 12 F/g and 8 F/g for Ni/C and Co/C samples, respectively. The synthesized compounds can become a promising electrode material for super capacitors with an electrolyte solution of H2SO4. PubDate: 2022-03-01
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Abstract: Fraunhofer diffraction of light by a slit on an opaque screen located between a vacuum and a homogeneous anisotropic medium in the absence and in the presence of absorption at different orientations of the optical axis of the medium relative to the slit is considered. The well-known formula for the diffraction in a vacuum is generalized, with the inclusion of the case of diffraction into a uniaxial anisotropic medium in the absence of absorption. A formula is obtained that makes it possible to determine the directions of the diffraction minima and maxima taking into account this absorption. PubDate: 2022-03-01
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Abstract: Non deterministic polynomial complete problems are playing an essential role in nowadays communications, security and many other fields. One of the well-known NP-complete problems is the Examination Timetabling problem. Given the information about the courses and the students that have taken some of those courses as well as the time slots for the exams of those courses the problem asks if there is a timetable such that no student has two exams simultaneously. We are modeling this NP-complete problem as a system of particles with one dimensional motion. After adding some interactions between the particles based on the problem we are simulating the motion and arriving to an equilibrium. We then use the equilibrium state to group the particles together where each cluster represents a time slot. To discuss the physics of this model we use the Replica method to find the free energy functional of this system. A hypothesis is formulated that all or at least most numerical solutions for NP-complete problems can be brought to this model with some configuration of interactions between the particles. PubDate: 2022-03-01
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Abstract: Using the probe antenna of the applicator, radio frequency signals (RFS) of the human brain are recorded. A method for digital processing of recorded RFS in the LabVIEW environment using spectral and bispectral analysis is proposed. As a result of spectral analysis, it was revealed that the human brain emits RFR in the megaHertz range, and as evidenced by the results of bispectral analysis, some groups of spectral components of RFR of the brain exhibit an internal correlation. The results of these studies can be useful for identifying fast processes in the human brain, for understanding the nature of these processes, and, as a result, for the diagnosis and treatment of various human diseases associated with the brain. PubDate: 2022-03-01
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Abstract: The conductivity of single-crystal nanoplates of the Sb2Te3 topological insulator has been investigated. A sharp drop in resistance occurs in ultrathin Sb2Te3 nanoplates at a temperature of about 4 K, which is a manifestation of superconductivity. The results show that the presence of an optimal degree of disorder is a necessary condition for the onset of superconductivity. A superconductor-insulator transition, tunable by a magnetic field, is observed in these nanoplates. The temperature dependence of the magnetoresistance in fields below the critical value (B < BC) shows a successive transformation of a weak antilocalization anomaly into a superconducting transition. The value of the correlation length exponent ν = 0.75 ± 0.05 was obtained using the scaling theory. PubDate: 2022-03-01
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Abstract: The results of theoretical modeling of the dynamics of a charged large molecule in an aqueous solution under the influence of gravity, vertical electric field, and drag force are presented. Computations were carried out for the DNA molecule. It is shown that one can smoothly control the speed of movement of a molecule by an electric field so that it is possible to carry out accurate sequencing by the tunneling current method. It was also shown that the speed of movement of a molecule can be reduced to some decimal cm/s, which is equivalent to sequencing 105–106 nucleoids per second. PubDate: 2022-03-01
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Abstract: Single wall version of carbon nanotubes (SWCNTs) is promising for the detection of many important gases including gases exhaled by the organism. Properties of such CNT-noble metal sensors, detectors of gases exhaled by the organism, biosensors and other applications of CNT sensors in medicine are reported. Very promising is the realization of gas sensors based on metal oxides (especially SnO2) doped with CNTs. VOC sensors based on ruthenate multi-walled carbon nanotubes coated with tin-dioxide nanoparticles (MWCNTs/SnO2) nanocomposite structures were prepared and investigated in Yerevan State University (YSU) using three methods. The optimal conditions, operating temperature and the mass ratio of the components are established for the manufacturing of acetone and toluene as well as ethanol and methanol vapors detectors. The results of research works related to the study of MWCNT-SnO2 nanocomposite sensors of propylene glycol (PG), dimethylformamide (DMF) and formaldehyde (FA) vapors are also presented in this paper. The dependence of the sensor response on gas concentration is linear. PubDate: 2022-03-01
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Abstract: This work describes the methodological part of the analysis on the study of the near-threshold quasi-real photoproduction of vector mesons on nucleons. The analysis uses experimental data obtained at the CLAS12 (Cebaf Large Acceptance Spectrometer) of the CEBAF (Current Beam Accelerator Facility) of the Jefferson Laboratory (USA). The experimental data on the scattering of 10.6 GeV electrons by a liquid hydrogen target is investigated. The work describes methods for the selection and identification of the final states of completely exclusive near-threshold reactions of (Eγ ≥ 8.2 GeV) quasi-real (Q2 ≈ 0) photoproduction of J/ѱ mesons. A step-by-step description of the mechanism for identifying the selection of the final state of a lepton pair and the recoil nucleon is presented. It is shown how the parameters of the distributions of kinematic quantities characteristic of the reactions under study change in the course of the analysis. PubDate: 2022-03-01
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Abstract: The tunneling passage of a microparticle with a spin through a three-dimensional delta potential embedded in a quantum wire with a characteristic effect of dimensional quantization is considered. This effect results in multichannel scattering, which does not occur in one-dimensional problems. The particle is also affected by a magnetic field directed along the wire which generally takes unequal constant values on both sides of the barrier. Analytical expressions for the scattering coefficients and the spin polarization coefficient of multichannel scattering are obtained. Several special cases of the obtained formulas are considered. The dependences of the mentioned coefficients on the particle energy, the parameters of the potential barrier and nanotube, and the magnetic field are investigated in a single-channel approximation in detail. PubDate: 2022-03-01
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Abstract: The paper proposes a new type of gas flowmeters based on measurements of the deformations of the thermal field of the heater in the presence of a flow using vibrating wires. The advantage of such flowmeters as compared with the known ones using a similar thermal principle of operation is the improved accuracy of temperature measurements compared to resistance thermometers or thermocouples. The use of thin wires can also increase the speed of flowmeters. The use of wires 20–30 mm long allows the creation of wide-aperture inlet holes for gas streams. A natural property of the developed flowmeters is also in their bidirectionality. A sample of a flowmeter based on vibrating wires was made and the calibration experiments were carried out. An experiment was carried out in which a flowmeter was used to measure the acceleration. PubDate: 2022-03-01
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Abstract: A direct current streamlined loop formed by two diametrically opposite spirals of a linear or ribbon wire is a deflector for nonrelativistic electrons and a spiral undulator for relativistic electrons. In this work, analytical expressions are obtained for the three components of magnetic induction inside a two-wire spiral line (TSL), which differ significantly from similar expressions used in scientific works. In particular, in the paraxial region, where electrons interact with the magnetic field, the radial component of the magnetic induction is not an increasing function of the radial coordinate, but a decreasing one. This result is important because the description of the physical characteristics of a free-electron laser or deflector requires taking into account the exact trajectories of the bunch electrons. The obtained correct formulas for the potential of the magnetic field and the components of the magnetic induction are also necessary to determine the values of the resonant frequencies of electromagnetic waves excited by a quasi-stationary sinusoidal voltage inside the TSL. PubDate: 2022-03-01
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Abstract: The X-ray Laue asymmetrical diffraction in a perfect crystal with a plane entrance surface is considered taking into account the third-order nonlinear response of a crystal. Using the exact solutions, the rocking curve dependence on the angular departure from the exact Bragg direction and the intensity of the incident wave is investigated. The dependence of rocking curves on the asymmetry degree of diffraction geometry is studied. The obtained results can be used in the preparation of X-ray beams with the given parameters and for object investigations as well. PubDate: 2022-03-01
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Abstract: Based on the linear electron accelerator LUE-75 of the A.I. Alikhanyan National Scientific Laboratory a technique for obtaining controlled primary electron beams with an intensity of 10–20 electrons per second in the energy range 15–75 MeV for elementary particle detectors calibration was developed and used. Joint work with the V.P. Dzhelepov Laboratory of Nuclear Problems (JINR, Dubna, RF) showed the efficiency of the technique. PubDate: 2022-03-01
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Abstract: The electroconvection (EC) phenomenon arising in nematic liquid crystals (NLC) of type E7 under the influence of an external electric field was recorded by the method of X-ray interferometry. The character of the refractive indices of the ordinary (no) and extraordinary (ne) waves is studied, and the moment of the appearance of EC in the NLC is determined. It is shown that the phenomenon of electroconvection occurs when no and ne coincide. It is also shown that in the E7 type NLC, where there are no free charge carriers, under the influence of an external electromagnetic field an EC phenomenon can occur as a consequence of the formation of bound charges. PubDate: 2021-10-01 DOI: 10.3103/S1068337221040083
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Abstract: In the present work single crystals of yttrium orthoaluminate (YAlO3) activated with Yb3+ ions and additional nonisovalent Li+ and Hf4+ impurities were grown. Comparative measurements of spectral characteristics of crystals including those exposed to gamma-ray irradiation were carried out to reveal the functional role of additional impurities. On the basis of the results obtained, the mechanisms of incorporation and charge compensation mechanisms of Li+ and Hf4+ ions in YAlO3:Yb are considered and the efficiency of using these impurities is shown to obtain crystals with a low concentration of anion vacancies and associated color centers. PubDate: 2021-10-01 DOI: 10.3103/S1068337221040125
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Abstract: The bandwidth in the system of the nonlinear optical crystal partially filling the cross-section of a rectangular metal waveguide is investigated. Partial filling of a metal waveguide with a nonlinear optical crystal is used to ensure the phase matching for an effective generation of THz radiation in a nonlinear crystal when it is illuminated with the femtosecond optical laser pulse. The critical wavelengths of a metal waveguide with a central symmetric arrangement of crystal plates in the waveguide are numerically calculated depending on the degree of partial filling and the dielectric permittivity of the crystal. It is shown that partial filling of the waveguide with crystal results in an expansion of the bandwidth of the fundamental mode of the odd type Н10, without improving the propagation conditions for the nearest higher even mode Н20, but on the contrary, at a certain degree of filling with the crystal excludes its occurrence. PubDate: 2021-10-01 DOI: 10.3103/S1068337221040113
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Abstract: The results of studies of many types of semiconductor H2O2 sensors are discussed in this review of 185 articles about hydrogen peroxide. The properties of electrochemical detectors, sensors based on organic and inorganic materials, graphene, and nano-sensors are analyzed. Optical and fluorescent sensors, detectors made of porous materials, quantum dots, fibers, and spheres are briefly discussed. The results of our studies in the YSU of hydrogen peroxide sensors made from solid solutions of carbon nanotubes with semiconducting metal oxides are also presented in the review. The fundamentals of the manufacture of biomarkers of respiration containing hydrogen peroxide vapors, which make it possible to judge the degree of a person’s illness with various respiratory diseases (asthma, lung cancer, etc.), are discussed. PubDate: 2021-10-01 DOI: 10.3103/S1068337221040046
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Abstract: The work is devoted to the study of the behavior of heterogeneous biopolymers during the melting of the secondary structure. A random bimodal biopolymer is generated. Each component corresponds to its transfer matrix of GMPC, by multiplying these transfer matrices the free energy of the system is calculated. It is shown that for a length of 5000 repeating units, the reduced free energy does not depend on the realization of the system (primary structure). The corresponding denaturation curves show that the transition point is well defined as a linear combination of the corresponding homopolymers, but the profile of the curves depends on the implementation. The behavior of the number of junctions between the helical and coiled states is calculated. An unexpected result is obtained that the racemic heteropolymer with a length of 5000 repeated units is divided into about 10 sections during the melting process. We associate this with the behavior of correlation in the system, which will be investigated further. PubDate: 2021-10-01 DOI: 10.3103/S106833722104006X
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Abstract: A consistent approach is developed to the description of a scalar wave field generated by a system of point coherently emitting sources. In particular, the problem of the maxima and minima of the intensity of the superposition field under the conditions of Fraunhofer diffraction is discussed. The problem of determining the serial number of the wave field maxima is investigated. Generalization of the classical result related to interference, when an initial phase shift is present at two sources, is carried out. PubDate: 2021-10-01 DOI: 10.3103/S1068337221040095
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Abstract: A device based on a three-block Fresnel zone plate interferometer is proposed for hard X‑ray phase-contrast imaging. The device combines a low requirement for the coherence of the initial radiation (the interferometer operates in the amplitude division mode) with an optical magnification of the image. A numerical simulation of the image formation is carried out, taking into account the limited source–interferometer distance, the size and spectral width of the X-ray source. The calculations show that the proposed set-up can be used as a phase-contrast microscope using laboratory hard X-ray sources. PubDate: 2021-10-01 DOI: 10.3103/S1068337221040058
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