bluuebunny/crossref_metadata_2025 huggingface dataset:
Impact of Yoga on Immune Response with Special Reference to COVID- 19: A Review of Randomized Controlled Trials
Authors: Mishra Neha , Mishra Saurabh
Published: January 2023

Like other viruses, severe acute respiratory syndrome coronavirus-2 (SARS-CoV- 2) continuously evolves due to mutations during genome replication. These mutations lead to various new variants and may alter the pathogenicity, immune escape capacity, and re-infection risk. In addition, it is also evident that a compromised immune system increases the susceptibility and severity of the disease. Therefore, strengthening the immune system is considered to combat Covid. Yoga is an ancient practice used for strengthening the body and mind. There are abundant studies that focus on yoga's benefits for stress management; however, lesser studies observed the effects of yoga on the immune system. Therefore, the present study aims to compile randomized controlled studies on the role of yoga in immunity and COVID-19. Our finding reported moderate evidence for the benefits of yoga in the levels of inflammatory markers, such as C-reactive protein (CRP), and cytokines, such as interleukin (IL) and tumor necrosis factor-alpha (TNF-α). However, lesser shreds of evidence were observed on the effect of yoga on innate and adaptive immunity. Our finding reported a paucity of studies examining the impact of yoga on the immunity of Covid patients. Thus, its efficacy as a potential adjuvant to attenuate Covid-19 infection has yet to be proven. Further extensive studies are recommended to draw the inference on the impact of yoga on COVID-19.
Monitoreo de la salud estructural de un edificio residencial de muros de corte de hormigón armado en Lima, Perú, utilizando un sensor 4d raspberry shake
Authors: Sifuentes Jiménez Armando Israel , Suarez Antunez Mary Criss , Estacio Flores Lucio Eduardo
Published: January 2023

Lima, the capital of Peru, has not suffered from a great earthquake since 1746, making this a prone Mw 8.8 earthquake area according to seismological studies. In this context, seismic structural health monitoring presents an opportunity to assess rapidly buildings after a great earthquake and protect inhabitant from those buildings with high risk of collapse due to aftershocks. A basic seismic structural health monitoring arrangement of a fifteenth-floor residential building is presented using a low-cost sensor called Raspberry Shake 4D. The implemented sensor incorporates both a vertical velocity geophone and three orthogonally positioned microelectromechanical systems accelerometers. The building is a reinforced concrete shear walls structure located in Comas, north of Lima. More than thirty seismic events have been recorded, including the Mw 8.0 Lagunas earthquake (05/26/2019) and the Mw 5.8 (22/06/2021) with epicentral distances of 709 km and 94 km, respectively. Acceleration as high as 150 cm/s2 and as low as 2 cm/s2 have been recorded. It was possible to obtain fundamental frequencies of vibration in longitudinal and transversal directions of the building from the response calculated using the wavelet transform that have a good agreement with results of microtremor measurements performed at different floors. The computed scalograms for seismic records showed important values of energy amplitudes for the fundamental frequencies of the building. Finally, theoretical fundamental frequencies were obtained from a 3D finite element model and an elastic analysis.
Synthesis and Characterization of Cellulose Acetate and Nanocellulose Acetate from Sengon Agroindustrial Waste (Paraserianthes falcataria)
Authors:   Chemistry Department, Brawijaya University, Jl. Veteran 65145 Malang, Ikhtiarini Nur , Masruri Masruri ,   Chemistry Department, Brawijaya University, Jl. Veteran 65145 Malang, Mariyah Ulfa Siti ,   Chemistry Department, Brawijaya University, Jl. Veteran 65145 Malang, Widodo Widodo ,   Biology Department, Brawijaya University, Jl. Veteran 65145 Malang
Published: January 2023

Synthesis and characterization of cellulose acetate and nanocellulose acetate have been carried out. Cellulose was isolated from sengon wood powder waste using 6% NaOH solution and bleached with NaOCl. The cellulose was hydrolyzed with 60% formic acid to obtain nanocellulose. Cellulose and nanocellulose were then modified with acetic anhydride. The synthesized products were characterized by FTIR to identify organic functional groups, powder XRD to measure crystallinity, and SEM to observe surface morphology. Solubility tests in several types of solvents were also performed. The degree of substitution (DS) of cellulose acetate and nanocellulose acetate was carried out based on Indonesia’s SNI 0444:2009 method. The DS calculation show that the cellulose acetate and nanocellulose have DS of 2.9 and 2.1, respectively.
Iron Metal Ion Adsorption Capacity on Palm Oil Mill Effluent (POME) Using Montmorillonite Adsorbent
Authors:   Department of Chemistry, Faculty of Engineering, Universitas Samudra, Dayanti Mellanie Maria , Harmawan Tisna ,   Department of Chemistry, Faculty of Engineering, Universitas Samudra, Wahyuningsih Puji ,   Department of Chemistry, Faculty of Engineering, Universitas Samudra
Published: January 2023

Palm oil mill effluent (POME) is the most produced waste among other types of waste, which is around 60% in every 100% processing of fresh fruit bunches containing heavy metals, namely ferrous metal (Fe). Montmorillonite (MMT) is one of the best adsorbents used to reduce the concentration of Fe in POME. In addition, this mineral (MMT) also has a high cation fertilization capacity so that the space between layers of MMT is able to accommodate large amounts of cations and make MMT a unique material. In this review, the assurance of the mass variety of the MMT as adsorbent and the variety of the contact time on the adsorption capacity of Fe metal in POME was resolved utilizing a Atomic Absorption Spectrophotometer (AAS) and surface morphology analysis of MMT before and after adsorption using Scanning Electron Microscope (SEM). Based on the results of AAS analysis, the greater the mass of the adsorbent, the higher the amount of Fe adsorbed from the POME. Moreover, the longer the contact time between MMT and Fe, the higher the amount of Fe in the palm oil mill effluent adsorbed on the adsorbent surface. The best adsorption conditions occurred at an adsorbent mass of 8.5 g MMT in 50 mL adsorbate and a contact time of 5 hours with an adsorption capacity of 0.0383 mg/g. The results of the SEM showed the presence of empty spaces in the MMT before adsorption, in which after adsorption white granules occupies the empty spaces evenly on the surface of the MMT. The granules indicate the presence of Fe metals in the POME samples which are adsorbed on the MMT surface.
Synthesis of Struvite Crystal (MgNH4PO4.6H2O) from Laundry Waste to Consider its Potential as a Plant Fertilizer: Stirring and Processing Temperature Effect
Authors:   Department of Chemical Engineering, Faculty of Engineering, Universitas Pembangunan Nasional “Veteran”  Jawa Timur (UPN), Gunung Anyar, Surabaya 60294, Indonesia, Suci Perwitasari Dyah , Aini Fauziyah Nur ,   Department of Chemical Engineering, Faculty of Engineering, Universitas Pembangunan Nasional “Veteran”  Jawa Timur (UPN), Gunung Anyar, Surabaya 60294, Indonesia, Sampe Tola Pardi ,   Department of Food Technology, Faculty of Engineering, Universitas Pembangunan Nasional “Veteran” Jawa  Timur (UPN), Gunung Anyar, Surabaya 60294, Indonesia
Published: January 2023

This paper aimed to process phosphate from laundry waste to be struvite crystal by precipitation and crystallization methods. In general, phosphates are difficult to remove by conventional treatment technologies. Therefore, precipitation and crystallization methods can be an alternative choice for phosphate recovery. Precipitation and crystallization methods by adding KOH can serve to remove dissolved phosphate content in wastewater, as well as convert it into a solid form that can be reused as industrial raw materials. The research variables used were stirring temperature (25, 30, and 35 C) and stirring speed (100, 125, 150, and 200 rpm). By using X-ray Fluorescence (XRF) and Scanning Electron Microscope (SEM-EDX), the analysis showed that the highest percentage of phosphate removal was at a stirring speed of 100 rpm at 30°C, which was 47.5%. X-ray Diffraction (XRD) was also carried out on several samples and it was confirmed that the dominant crystal phase formed was a struvite (MgNH4PO4.6H2O) for all samples, and secondary phase magnesium phosphate hydrate (Mg3(PO4)2.8H2O was found in a stirring speed of 100 rpm at 30°C. The morphology of the struvite crystals formed resembles irregular flakes by using SEM.
Pyroelectric coefficient estimations for aluminum and gallium compounds
Authors: Davydov C. Yu.
Published: January 2023

Analytical expression for pyroelectric coefficient p for the compounds with wurtzit structure is given. Obtained values of p for AlN and GaN are in satisfactory agreement with the first-principles calculations. Pyroelectric effect in the uniform epitaxial films and heterostructures is discussed. Keywords: pyroelectric coefficient, wurtzite structure, monocrystal, thin film, heterostructure.
Thermodynamic Properties and Phase Transitions of Multiferroics (1-x)BiFeO-=SUB=-3-x-=/SUB=-PbFe-=SUB=-0.5-=/SUB=-Nb-=SUB=-0.5-=/SUB=-O-=SUB=-3-=/SUB=-
Authors: Kallaev S. N.  , Omarov Z. M.  , Bilalov A. R.  , Pavlenko A. V.
Published: January 2023

Studies of the heat capacity and dielectric properties of (1-x)BiFeO3-xPbFe0.5Nb0.5O3 ceramic multiferroics in the temperature range of 300-800 K were carried out. Based on studies of the temperature and concentration dependences of the heat capacity and dielectric constant, the phase transition temperatures of the (1-x)BiFeO3 system were determined. (1-x)PbFe0.5Nb0.5O3 with various x concentrations. It is shown that with an increase in the PbFe0.5Nb0.5O3 component, the temperatures of the ferroelectric and antiferromagnetic transitions in BiFeO3 shift to low temperatures. Taking into account structural studies, a "temperature-concentration" phase diagram has been constructed. Keywords: heat capacity, dielectric properties, ferromagnet, antiferromagnet, multiferroics.
Heat capacity of nanostructured SmFeO-=SUB=-3-=/SUB=-
Authors: Mitarov R. G.  , Kallaev S. N.  , Omarov Z. M.  , Khizriev M-Sh. C.  , Abdulvakhdov K. G.
Published: January 2023

The temperature dependence of the heat capacity of nanostructured SmFeO3 ceramics obtained by mechanical activation in the temperature range of 120-800 K has been studied. It has been shown that the excess heat capacity of mechanically activated ceramics is due to: displacements of iron and samarium ions and with a change in the angle between FeO6 oxygen octahedra. Keywords: multiferroics, heat capacity, samarium ferrite, Schottky heat capacity, nanostructured ceramics, mechanical activation.
The Effect Of A Strong Static Electric Field And Heating On Characteristics Of The High-Frequency Impedance Of Metal--Ferroelectric--Semiconductor Structures
Authors: Belorusov D.A.  , Goldman E.I.  , Chucheva G.V.
Published: January 2023

Studies have been carried out on the effect of heating and a strong field, but pre-breakdown, effects on high-frequency characteristics of the impedance of heteroepitaxial structures Ni-Ba0.8Sr0.2TiO3-pSi with a ferroelectric thickness of 50 nm. It was shown, that regardless of the polarity of the field stress, characteristics shifted towards a positive bias, and the width of hysteresis loops decreased; plateau levels remained virtually unchanged. Heating up to 121oC led to a change in levels of the upper plateau of characteristics: for the capacity it decreased, and for the conductivity it increased; branches on the loop not only narrowed and shifted, but changed places in comparison with the original dependence (loop reverse). These results can be explained: under the field action, by the generation of additional electronic states, localized in the buffer layer at the Si-Ba1-xSrxTiO3 interface, and by heating, by the appearance of delay effects due to the development of fluctuation processes, underlying the smearing of the phase transition from ferroelectric to paraelectric condition. Keywords: High-frequency field characteristics of the impedance, the field stress, hysteresis loops, the generation of additional localized electronic states, delay effects, fluctuation processes, smearing of the phase transition.
Elasticity of 3D and 2D XC (X = Si, Ge, Sn) compounds: Keating and Harrison models
Authors: Davydov C. Yu.
Published: January 2023

For the bulk and monolayer IV group carbides in the scope of Keating and/or Harrison models analytical expressions are obtained for second order elastic constants cij, sound velocities v, third order elastic constants cijk, pressure dependencies of cij and v, Grneisen constant, thermal expansion coefficient and temperature dependence of bulk moduli. It is shown that in the row of SiC-GeC-SnC values of all considered characteristics decrease while thermal expansion coefficient increases. All the model estimations are compared with experimental data and calculating results of other authors. Keywords: force constants, elastic constants, sound velocities, anharmonic characteristics.
Conditions of elastic mechanical stability and elastic properties of crystal structures with different symmetry
Authors: Gusev A. I.  , Sadovnikov S. I.
Published: January 2023

A critical analysis of the conditions of elastic stability of crystal structures of different symmetry as restrictions imposed on their elastic constants cij has been carried out. It is shown that the conditions of elastic stability of all crystals, except for cubic ones, are described by polynomials from the second to sixth powers of their elastic constants cij. Necessary and sufficient conditions for the elastic stability of crystals of different symmetry are presented explicitly. Keywords: Elastic stability, Symmetry, Elastic constants, Stability conditions.
Wideband EPR spectroscopy of Y-=SUB=-3-=/SUB=-Al-=SUB=-5-=/SUB=-O-=SUB=-12-=/SUB=- : Ho-=SUP=-3+-=/SUP=- crystals
Authors: Asatryan G.R.  , Shakurov G.S.  , Petrosyan AG.  , Kramushchenko D.D.  , Hovhannesyan K.L.
Published: January 2023

EPR spectra of Ho3+ impurity ions were recorded in single crystals of yttrium aluminum garnet (Y3Al5O12) in the frequency range of 114-170 GHz, at a temperature of 4.2 K. The measurement results indicate the substitution of Ho3+ ions for Y3+ ions in the dodecahedral position with D2 local symmetry. The magnitude of the g-factor, the hyperfine structure constant, and the energy interval between the main and the first excited nondegenerate sublevels of the main multiplet 5I8 are determined. Weak satellite signals have also been registered, the origin of which is associated with the formation of antisite defects in the environment of Ho3+ paramagnetic centers. Keywords: hyperfine interaction, rare earth ions, spin Hamiltonian, non-Kramers ion.
Electronic structure of vacancy-type defects in hexagonal boron nitride
Authors: Perevalov T. V.  , Gritsenko V. A.  , Bukhtiyarov A. V.  , Prosvirin I. P.
Published: January 2023

The electronic structure of vacancy-type defects in hexagonal boron nitride (h-BN) synthesized by chemical vapor deposition, promising for microelectronics, is studied. The research is carried out using X-ray photoelectron spectroscopy and a simulation within the density functional theory. It is shown that the h-BN bombardment with argon ions leads not only to the near-surface layer cleaning from organic pollutants, but also to the generation of a high intrinsic defects concentration, mainly boron-nitrogen divacances. The greater the boron-nitrogen divacances concentration is, the longer the bombardment time is. The boron-nitrogen divacansion in h-BN is a significantly more energetically favorable defect than that of isolated boron and nitrogen vacancies. It is concluded that the most probable diamagnetic vacancy-type defects capable of participating in localization and, as a consequence, in charge transport in h-BN films is the boron-nitrogen divacancy. Keywords: boron nitride (BN), photoelectron spectroscopy (XPS), quantum chemical simulation, density functional theory (DFT).
Effect of iso- and heterovalent cation substitutions on the superionic Faraday transition in fluorite-type modification β-PbF-=SUB=-2-=/SUB=-
Authors: Sorokin N. I.
Published: January 2023

The influence of isovalent substitutions of Pb2+-> Cd2+ and heterovalent substitutions of Pb2+-> Sc3+ on a superionic Faraday transition in Pb1-xCdxF2 (x=0.33) and Pb1-xScxF2+x (x=0.1) solid solutions based on the fluorite-type modification β-PbF2 with sp. gr. Fm 3 m has been studied. The Faraday phase transition can be characterized by the temperature Ttrλ corresponding to maximum on the heat capacity curve and temperature Ttrα corresponding to the beginning of the structural disorder anion sublattice. Both of these temperatures are found on the temperature conductivity dependence sigmadc(T) of β-PbF2, Pb0.67Cd0.33F2 and Pb0.9Sc0.1F2.1 crystals. The values of Ttrλ and Ttrα in solid solutions compared with β-PbF2 (Ttrλ=715±10 K, Ttrα = 597±12 K) decrease by 100-110 and 30-45 K for Pb0.67Cd0.33F2 and Pb0.9Sc0.1F2.1, respectively. Decreasing of temperature Ttrλ leads to an increase in temperature interval of existence of the superionic state. For T>Ttrλ the anionic conductivity of fluorite-type Pb0.67Cd0.33F2, Pb0.9Sc0.1F2.1, and β-PbF2 crystals reaches anomalously high values of sigmadc = 1-2 S/cm (873 K) at an ion transfer activation enthalpy equals to Hsigma~0.3 eV. Keywords: phase transitions, fluorides, fluorite structure, ionic conductivity, solid solutions.
Magnetovolume effects and thermal expansion in chiral helical ferromagnets Fe-=SUB=-1-x-=/SUB=-Co-=SUB=-x-=/SUB=-Si
Authors: Povzner A .A.  , Volkov A. G.  , Nogovitsyna T. A.  , Bessonov S. A.
Published: January 2023

Within the framework of the theory of band magnetism and the Heine model for the volume dependence of the electronic spectrum, an approach is being developed to study magneto-volume effects in chiral helical ferromagnets. Using Fe1-xCoxSi as an example, it was found that in the range of long-range order (at temperature T<Tc) the magnetovolume effect is determined by the amplitude of helicoidal spin spirals and leads to the experimentally observed negative volume thermal expansion coefficient. In the region of phase transitions of the first order (from Tc to Ts) prolonged in temperature, a new mechanism of the magnetovolume effect is established due to the spatial fluctuations of spin spirals arising due to the difference in the Hubbard potentials of iron and cobalt. It is shown that the considered volume effects lead not only to the experimentally observed negative volume thermal expansion coefficient (VCTE) in the chiral spin short-range order phase, but also to a noticeable increase in the transition temperature to the paramagnetic state (T>Ts). Keywords: helicoidal ferromagnetism, chirality, spin fluctuations, electronic and crystal structure, thermal expansion.
First-Principles Study of the Physical Properties of CuV-=SUB=-2-=/SUB=-S-=SUB=-4-=/SUB=- under Pressure
Authors: Rahman M Atikur.  , Lubna J. F.  , Sarker S.  , Khatun R.  , Saha S. Kumur.  , Rahaman M. Z.  , Hossain K. M.  , Rasheduzzaman M.  , Hasan M. Z.
Published: January 2023

The structural, electronic, mechanical, thermodynamic, and optical properties of CuV2S4 have been studied under pressure (0-50 GPa) by employing first-principles computation depending on the density functional theory. The optimized structural constraints are in good accord with the experimental results. By employing different pressure, the variation of single crystal elastic constant Cij as well as polycrystalline mechanical parameters are evaluated and discussed in detail. The increment of elastic constant with the increase in pressure guaranteed that CuV2S4 turn ought to be more resilient to shear distortion with pressure. The linear response of elastic moduli under pressure confirms that hardness of CuV2S4 rises with increasing pressure. The Pugh's ratio ensured the ductile nature of CuV2S4. Band structure and DOS calculations have been confirmed the electrically conductive nature of CuV2S4. The population analysis validates the presence of dominant covalent bonding. Optical properties, i.e., absorption, conductivity, reflectivity, and loss function are also explored with the variation of pressure. These optical functions demonstrate that the compound exhibits high reflectivity in the low-energy range, which assures the application of this compound as coating material. The thermodynamic properties are also investigated under pressure and discussed. Keywords: first-principles study, spinel-type compound CuV2S4, mechanical properties, electronic properties, optical and thermal properties.
A mechanism of pulse breakdown evolution in polymeric films
Authors: Semenov S. E.  , Kapralova V. M.  , Pakhotin V. A.  , Sudar N. T.
Published: January 2023

We present the results of an experimental study of the pulse electrical strength of polyethylene terephthalate and polypropylene films when they are subjected to a single electric pulse. It has been found that the breakdown of these films is possible both at the front and at the plateau of the pulse, and the probability of breakdown at the front increases with pulse amplitude. We recorded a jump in the durability of the films at the transition from breakdown at the front to breakdown at the pulse plateau. It is shown that the processes that prepare the film electrical breakdown develop faster at the pulsefront than at the plateau. We discuss a possible physical mechanism to explain this effect. Keywords: polymers, polypropylene, polyethylene terephthalate, pulsed electrical breakdown, electroluminescence.
Structural and spectral characteristics of La-=SUB=-0.99-x-=/SUB=-Y-=SUB=-x-=/SUB=-Eu-=SUB=-0.01-=/SUB=-BO-=SUB=-3-=/SUB=- orthoborates
Authors: Shmurak S. Z.  , Kedrov V. V.  , Kiselev A. P.  , Fursova T. N.  , Zver'kova I. I.
Published: January 2023

The structure, IR absorption, luminescence, and luminescence excitation spectra of La0.99-xYxEu0.01BO3 orthoborates synthesized at 970oC were studied at 0≤ x≤0.99. An increase in x leads to a sequential change of the structural state of these compounds. At 0≤ x≤0.1, the samples are single-phase and have the aragonite structure. Within the range of 0.1<x≤0.8, the samples are two-phase: the vaterite phase is observed along with the aragonite structure. At 0.8<x≤0.99, the samples are single-phase and have the vaterite structure. Correspondence between the structure and spectral characteristics of these compounds was established. It is demonstrated that with an increase in the Y3+ concentration, the vaterite phase is formed first in the bulk of microcrystals having the aragonite structure and then in the entire sample. It is shown for the first time that a band with the maximum of 469 nm is observed in the luminescence excitation spectrum (LES) of samples having the vaterite structure and is absent in samples having the aragonite structure. It is revealed that a band in the luminescence spectrum, corresponding to the ^5D_0->^7F0 electron transition, as well as 469 nm-band in the LES, can be an indicator of the structural state of the sample. Keywords: rare earth orthoborates, X-ray diffraction analysis, crystal structure, IR spectroscopy, luminescence spectra.
Paramagnetic centers in chromium-doped scandium orthosilicate
Authors: Vazhenin V. A.  , Potapov A. P.  , Fokin A. V.  , Artyomov M. Yu.  , Isaev V. A.
Published: January 2023

The EPR spectrum of single crystals of scandium orthosilicate doped with chromium was studied in the X-band. In the crystallographic and local coordinate systems, the parameters of the spin Hamiltonians of two Cr3+ centers that have replaced scandium in the nonequivalent triclinic positions and demonstrate orthorhombic symmetry in the principal axes are determined. The spectrum of the Gd3+ center localized in one of scandium position was discovered and studied, and the parameters of the fine structure of its ground state were determined. In the studied crystals, EPR signals of unidentified paramagnetic centers also were observed. Keywords: scandium orthosilicate, impurity ions, paramagnetic resonance.
Magnetocaloric effect in amorphous-crystalline microcircuits PrDyFeCoB
Authors: Dvoreckaia E. V.  , Sidorov V. L.  , Koplak O. V.  , Korolev D. V.  , Piskorsky V. P.  , Valeev R. A.  , Morgunov R. B.
Published: January 2023

In amorphous-crystalline PrDyFeCoB microconductors obtained by ultrafast melt cooling, a negative magnetocaloric effect was detected at 200-250 K (with heat release when the magnetic field is turned on), as well as a positive magnetocaloric effect in the temperature range of 300-340 K (with heat absorption when the magnetic field is turned on). It is established that there are no phase transitions of the first kind in the studied temperature range, which indicates that both of the detected effects are associated with a change in the magnetic part of the entropy. The transition at 200-250 K is due to the presence of metamagnetic states induced by a magnetic field in the spin-glass state of the amorphous part of the PrDyFeCoB alloy, and with their transition to the ferrimagnetic state. The transition at 300-340 K is spin-reorientation, and it occurs in crystalline inclusions identified in the amorphous matrix. Keywords: spin-reorientation transition, spin glass, magnetocaloric effect, entropy. Keywords: spin-reorientation transition, spin glass, magnetocaloric effect, entropy.
The influence of transverse π-π-bridging on formation properties of high-modulus fibers of carbon nanotubes
Authors: Kozlov G.V.  , Dolbin I. V.
Published: January 2023

The theoretical model, treating increasing of elastic modulus of fibers from carbon nanotubes at introduction of transverse π-π-bridging between separate nanotubes in fiber. It has been shown that on elastic modulus of fiber three factors influenced, namely, elastic modulus of starting nanotubes, level of interactions between separate nanotubes in fiber and its aspect ratio, i.e. the ratio of fiber length to its diameter. In transition point of the indicated interactions from repulsion to attraction the elastic modulus of fiber achieves the value of corresponding parameter individual carbon nanotube and in region of attractive interactions exceeds it. The structure of fibers, characterized by their fractal dimension, is basic factor for stiffness of fibers of carbon nanotubes. Keywords: fiber, carbon nanotubes, π-π-bridging, nanotubes interactions, structure, elastic modulus, fractal dimension.
Estimating the Dimensions of Nanocrystalline Elements of the Polyethylene Structure by Differential Scanning Calorimetry
Authors: Egorov V. M.  , Borisov A. K.  , Marikhin V. A.  , Myasnikova L. P.  , Gurieva S. A.  , Ivankova E. M.
Published: January 2023

A method is proposed for calculating the dimension distribution of nanocrystalline elements of the lamellar and fibrillar morphologies of a polymer. Calorimetric data were used to calculate the distribution of the longitudinal size of these elements in lamellae and microfibrils of ultrahigh molecular weight polyethylene. The calculation results are consistent with the data obtained by the X-ray method.. Keywords: heat capacity, dimension effect, lamella, microfibril, polyethylene.
Energy analysis of magnetic structures of the ground state of the Potts model with competing exchange interactions
Authors: Ramazanov M.K.  , Murtazaev A.K.  , Magomedov M.A.  , Kurbanova D.R.  , Ramazanov K.M.  , Khizriev M.-Sh.S.
Published: January 2023

Based on the Wang--Landau algorithm, the Monte Carlo method was used to study the magnetic structures of the ground state and the thermodynamic properties of the two-dimensional Potts model with the number of spin states q=4 on a triangular lattice, taking into account the exchange interactions of the first J1 and second J2 nearest neighbors. The studies were carried out for the value of the interaction of the second nearest neighbors in the range -2.0≤ J2≤0.0. The magnetic structures of the ground state are constructed in the interval considered. An energy analysis of the magnetic structures of the ground state has been carried out. A phase diagram of the dependence of the critical temperature on the value of J2 is constructed. It is shown that taking into account the interactions of the second nearest neighbors leads to the appearance of frustrations and violation of the magnetic ordering. Keywords: Frustrations, magnetic structures, Monte Carlo method, Potts model.
On the derivation of the Belomestnykh--Tesleva's formula
Authors: Darmaev M.V.  , Sangadiev S.Sh.  , Mashanov A.A.  , Kim T.B.
Published: January 2023

The Belomestnykh--Tesleva's formula is interesting in that it establishes an unambiguous relationship between the Poisson's ratio and the Gruneisen's parameter. The derivation of this formula from the generally accepted Gruneisen's equation is discussed. The Belomestnykh--Tesleva's formula, obtained earlier from other assumptions, is derived using the theory of elasticity and the Leontiev's equation. For a number of silicate glasses and glassy metaphosphates of alkaline earth metals, the proposed approach finds a fairly satisfactory agreement with the experimental data. Keywords: Gruneisen's equation, Gruneisen's parameter, Poisson's ratio, shear modulus, isothermal bulk modulus, acoustic wave velocities.
Anomalous structural transformations of Gd-=SUB=-2-=/SUB=-O-=SUB=-3-=/SUB=- nanopowders obtained in the combustion mode by the glycine-nitrate method
Authors: Shmytko I. M.  , Kedrov V. V.
Published: January 2023

The structural states of Gd2O3 and Gd2O3 : 2% Eu3+ synthesized by the glycine-nitrate method were studied. As a result of this synthesis, in addition to the known cubic modification of gadolinium oxide, two new previously unknown phases are formed. The first phase is formed during prolonged exposure at room temperature of the initial nanocrystalline cubic structure obtained at a synthesis temperature of 650oC. The second phase has orthorhombic syngony and is formed during either long-term synthesis at a temperature of 650oC, or short-term syntheses at a higher temperature. Both phases pass into the traditional cubic modification during further high-temperature annealing. In addition, the effect of structural "infection" was found, which consists in the fact that during annealing of the cubic phase of Gd2O3 doped with Eu3+ ions in the range of 800-1100oC, its partial transition into the monoclinic phase occurs, which disappears with a further increase in the annealing temperature. Keywords: synthesis of Gd2O3, glycine-nitrate method, nanocrystalline state, X-ray diffraction research methods, phase transitions.
Morphological features of micro- and nanoporous silver and copper films synthesized by the substitution reaction method
Authors: Bezrukov P. A.  , Nashchekin A. V.  , Nikonorov N. V.  , Sidorov A. I.
Published: January 2023

The results of a study of the structural features of thin silver and copper films synthesized by the chemical substitution reaction are presented. Silver films were obtained by immersing copper substrates in a solution of silver nitrate. Copper films were synthesized by immersing iron and tin-plated iron substrates in a copper sulfate solution. The study of the morphology and composition of the synthesized layers was carried out using a scanning electron microscope. It has been shown that metal nanoporous layers up to 1 μm thick are formed on the substrates as early as 2-3 s after the start of the reaction. The layers consist of microcrystalline hexagonal plates and micro- and nanodendrites. As the reaction time increases, the layers become denser. In this case, the minimum pore size is 20 nm. The synthesized nanoporous films can be used for photocatalytic decomposition of water and enhancement of Raman scattering. Keywords: morphology, porous film, silver, copper, substitution reaction.
Effect of gold intercalation on the electronic structure of graphene on Co-Si/SiC(0001)
Authors: Rybkina A. A.  , Filnov S. O.  , Glazkova D. A.  , Vilkov O. Yu.  , Bokai K. A.  , Pudikov D. A.  , Shikin A. M.  , Rybkin A. G.
Published: January 2023

Graphene grown on an ultrathin CoSi/CoSi2 silicide layer atop a SiC(0001) substrate and intercalated by Au was studied. Intercalation of Au was found to occur at a temperature of 500oC, and it is accompanied by the formation of gold silicide under graphene with a stoichiometry close to Au2Si. The study of the electronic structure of the system in the region of the (K) point of the surface Brillouin zone revealed the quasi-freestanding character of graphene with a linear spectrum of π states and a Dirac point near the Fermi level. Photoelectron microscopy revealed the homogeneity of the work function along the surface of the sample on a micrometer scale. Keywords: Graphene, magneto-spin-orbit graphene, intercalation, photoelectron spectroscopy, electronic structure.
Magnetization induced second harmonic generation in thin films with ferromagnet/antiferromagnet interfaces
Authors: Radovskaia V. V.  , Maydykovskiy A. I.  , Novikov V. B.  , Kopylov D. A.  , Gusev N. S.  , Pashen'kin I. Yu.  , Murzina T. V.
Published: January 2023

We experimentally studied the generation of optical second harmonic (SH) and magneto-optical effects at the SH frequency in thin films consisting of ferromagnetic and antiferromagnetic materials, including exchange-bonded layers, one of which is pinned with an antiferromagnetic layer. As expected, the loops of the linear magneto-optical Kerr effect are shifted relative to the zero magnetic field value, which reflects the presence of a pronounced exchange interaction in such structures. It is shown that in the case of the nonlinear Kerr magneto-optical effect this effect is also present, but it is significantly smaller than in the nonlinear case, and leads to the observation of only one hysteresis loop instead of two. The studied dependence of the magneto-optical response at the TH frequency on the probing laser radiation power demonstrates that its growth leads to a decrease in the magnetic hysteresis loop shift of the TH. Keywords: magnetization-induced SHG, ferromagnet/antiferromagnet interface, pinned structure, thin films
Superconducting thin films and tunnel junctions based on aluminum
Authors: Tarasov M. A.  , Chekushkin A. M.  , Fominsky M. Yu.  , Zaharov D. M.  , Lomov A. A.  , Devitsky O. V.  , Gunbina A. A.  , Sohina E. T.  , Edelman V. S.
Published: January 2023

The features of conductivity in aluminum films produced by various methods are described depending on the presence of impurities, film thickness, and deposition conditions. The results of measuring the surface properties and crystal structure of fabricated films of aluminum, aluminum oxide, and aluminum nitride by X-ray diffraction and atomic force microscopy are presented. SIS, SIN, NIN junctions based on aluminum were fabricated using both shadow evaporation and magnetron sputtering. The current-voltage characteristics were measured. The prospects for improving the characteristics of aluminum SIS junctions, SQUID amplifiers, and SINIS detectors operating at temperatures of about 100 mK are discussed. Keywords: aluminum thin films, surface roughness, atomically smooth films, tunnel junctions.
Energy of formation of intrinsic defects and their clusters in the powellite CaMoO-=SUB=-4-=/SUB=-
Authors: Dudnikova V. D.  , Antonov D. I.  , Zharikov E. V.  , Eremin N. N.
Published: January 2023

Atomistic simulation of powellite crystals has been carried out. A system of parameters of interatomic potentials is proposed for the calculation of point defects in powellite. The formation energies of intrinsic defects and their clusters, which are spatially related combinations of defects, are estimated. The most favorable localization of interstitial calcium and oxygen ions was determined. The formation energies of the Frenkel and Schottky defects are calculated. It was shown that the most energetically preferred in stoichiometric powellite are the oxygen Frenkel defects. Defects arising from deviations from stoichiometry are considered. It is established that the clustering of defects allows to reduce the energy of their formation by 15-20%. Keywords: powellite, tungstates and molybdates, atomistic simulation, intrinsic defects.
The study of phonon thermal conductivity of CoSi-CoGe solid solutions using ab initio lattice dynamics
Authors: Pshenay-Severin D. A.  , Konstantinov P. P.  , Burkov A. T.
Published: January 2023

Lattice thermal conductivity of solid solutions based on cobalt monosilicide and monogermanide was studied. Electrical and thermal conductivities of CoSi and solid solutions of CoGexSi1-x (x=0.03 and 0.07) were experimentally measured in the temperature range of 80-350 K. Phonon spectra and thermal conductivity in CoGexSi1-x solid solutions were calculated using ab initio lattice dynamics. The results of calculations are in good agreement with the results of measurements obtained in the present work and with the literature data. It was shown that already at a content of 10-15 at.% of Ge, the lattice thermal conductivity decreases by about a factor of 2 compared with pure cobalt monosilicide, and at a germanium content of about 70 at.%, the decrease can reach 3.5 times. Keywords: lattice thermal conductivity, thermoelectrics, first principle lattice dynamics.
Features of structure distortion at a phase transition in diluted YBaCo-=SUB=-4-y-=/SUB=-Zn-=SUB=-y-=/SUB=-O-=SUB=-7+x-=/SUB=- (y=0, 0.3) cobaltites
Authors: Kazei Z. A.  , Snegirev V. V.  , Stolyarenko M. S.  , Kamilov K. I.  , Khanov L. N.
Published: January 2023

Experimental studies of the lattice parameters, thermal expansion, and elastic characteristics in the range of the structural phase transition in the YBaCo4-yZnyO7+x series of cobaltites with diamagnetic dilution of the cobalt subsystem have been carried out. It has been found that for stoichiometric samples annealed in vacuum, the parameter Delta a/a shows no features during the structural transition, while the parameters Delta b/b and Delta c/c experience similar jumps of different signs. This leads to a jump in anisotropic (rhombic) εo~-4·10-3 and isotropic (volume change) Delta V/V~ -1·10-3 deformations. Upon substitution with Zn ions, the orthorhombic distortion of the structure changes slightly, and the jump in the volume anomaly (linear thermal expansion) changes sign. Structure distortion in stoichiometric samples is accompanied by characteristic anomalies in the Young's modulus Delta E(T)/E0 and internal friction in the TS range, while for nonstoichiometric quenched samples, the anomalies completely disappear. The diamagnetic substitution with Zn ions leads to a sharp decrease and then complete disappearance of the jump in the curve Delta E(T)/E0. This may be due to a change in the ratio of isotropic and anisotropic deformation during the structural transition upon a small substitution in the cobalt subsystem. Keywords: frustrated systems, cobaltites, structural phase transitions, lattice parameters, isotropic deformation, anisotropic deformation, thermal expansion, Young's modulus, internal friction.
The effect of hydrogen on the mechanical properties of metals under conditions of high-speed deformation
Authors: Malashenko V. V.
Published: January 2023

The movement of an ensemble of edge dislocations in metals with a high hydrogen content under conditions of high-speed deformation (high strain rate deformation) is theoretically analyzed. Within the framework of the theory of dynamic interaction of defects (DVD) (DID), an analytical expression is obtained for the dependence of the dynamic yield strength on the concentration of hydrogen atoms. Keywords: dislocations, hydrogen, high-speed deformation, metals.
Quantum mechanical calculation of electronic band structure of helically periodic systems: a case of nanotubes and nanohelicenes
Authors: Porsev V. V.  , Evarestov R. A.
Published: January 2023

A method for obtaining electronic bands in the helical Brillouin zone based on the results of high-level quantum mechanical calculations using the CRYSTAL17 software package is considered. Using the example of a carbon nanotube of chirality (4,1), the preference of helical Brillouin zone in comparison with the translational Brillouin zone is shown. For nanohelicene, a system which is helically periodic only, bands of electronic states were obtained corresponding to the structure closest to the energy minimum. In addition, the evolution of the electronic bands of nanohelicene depending on torsion distortions is presented. Keywords: line symmetry groups, electron bands, nanohelicene, carbon nanotube.
Spin and charge fluctuations in solid solutions of titanium substitution by iron group metals
Authors: Povzner A. A.  , Volkov A. G.  , Zaitseva N. A.
Published: January 2023

Topological electronic transitions from omega- to alpha-phase and from alpha- to beta-phase that occur with an increase in the concentration of substitution atoms in solid solutions of titanium with iron group metals are considered. It is found that due to the difference in the potentials of the Hubbard repulsion of titanium and substitution atoms, as well as temperature Bose excitations, spin and charge fluctuations of the electron density increase in the topological alpha phase. Accounting for fluctuations makes it possible to describe the concentration increase in the entropy of the phases of the titanium alloys under consideration at different temperatures. The amplification of electronic fluctuations with increasing temperature and concentration shifts the chemical potential beyond the topological area of the electronic spectrum, thereby suppressing the alpha phase and inducing an electronic transition to the beta phase. Using the example of calculations of the entropy of titanium substitution alloys with iron at different temperatures, a diagram of their structural phases is constructed, which is consistent with the available experimental data. Keywords: solid solutions, topological electronic transitions, spin and charge fluctuations, entropy, structural phases.
Structures and phase transitions in Fe-Ga-Al alloys
Authors: Balagurov A. M.  , Bobrikov. I. A.  , Sumnikov S. V.  , Yerzhanov B.  , Chubov D. G  , Palacheva V. V.  , Golovin I. S.
Published: January 2023

Evolution of structural phases and microstructural cast state of Fe100-(x+y)GaxAly compositions in the range of 17≤(x+y)≤39 at.% was studied in neutron diffraction experiments performed with high resolution and in continuous temperature scanning mode when heated to ~ 900oC and subsequent cooling. It is established that the structures of the cast states of triple alloys in the studied range of Ga and Al content basically repeat the structure of the double compositions Fe100-xGax up to x~ 30 and Fe100-yAly up to y~ 50. Namely, only cubic phases (A2, D03 and B2) are observed in them, and hexagonal (A3, D019) and monoclinic (such as Fe13Ga9 or α-Fe6Ga5) there are no phases characteristic of the Fe-Ga system. The expansion of the range of formation of cubic phases formed on the basis of the BCC cell in ternary alloys in comparison with Fe100-xGax indicates the role of Al in the stabilization of these structures. Keywords: alloys Fe-Ga, Fe-Al, Fe-Ga-Al, structural phase transitions, neutron diffraction, magnetostriction.
Electronic band structure, charge density distribution and chemical bonding in molecular crystals of chalcogens
Authors: Orlov V. G.  , Sergeev G. S.
Published: January 2023

The electronic band structure and the charge density distribution are theoretically studied in rhombohedral and monoclinic selenium, rhombohedral and orthorhombic sulphur with the aim to classify types of chemical bonding in molecular crystals of chalcogens. It is found that valence s- and lower in energy p-electrons contribute mainly in covalent bonds between nearest neighboring atoms in ring-shaped molecules, while all types of valence p-electrons provide bonding between rings of atoms in crystals. Parameters of critical points and the character of the charge density distribution in their vicinity point to coexistence of a number of types of chemical bonding in molecular crystals of Se and S: covalent, semimetallic and one more type, characterizing by the charge density fluctuations. Van der Waals forces, being important for finding equilibrium lattice parameters, have little impact on the charge density distribution and on the chemical bonding in crystals of chalcogens. Keywords: chalcogens, molecular crystals, electronic band structure, types of chemical bonding.
Magnetodielectric effect insingle crystals sequence of Pb-=SUB=-2-=/SUB=-Fe-=SUB=-2-x-=/SUB=-Mn-=SUB=-x-=/SUB=-Ge-=SUB=-2-=/SUB=-O-=SUB=-9-=/SUB=- (x=0-0.4)
Authors: Freydman A. L.  , Pankats A. I.  , Skorobogatov S. A.  , Horoshiy I. N.  , Kolkov M. I.
Published: January 2023

In this work, the magnetodielectric response have been studied in a series of single crystals of Pb2Fe2-xMnxGe2O9 with substitution x from 0 to 0.43. The research results showed that an increase in x leads to a change in the orientation of the antiferromagnetism vector in a zero magnetic field. The application of an external magnetic field leads to spin-flop and spin-reorientation magnetic transitions, which are accompanied by anomalies in the behavior of the permittivity.When Fe3+ ions are replaced by Mn3+ ions, the response of the magnetic subsystem to an external magnetic field changes, which is naturally reflected in the change in the magnetodielectric response. The permittivity changes stepwise when the magnetic subsystem passes into a state with a nonzero vector of the weakly ferromagnetic moment, or when its magnitude and orientation change due to a spin-flop transition. The latter indicates that a sharp change in polarizability is a consequence of a change in the contribution of the exchange energy, as well as the contribution of the Dzyaloshinskii-Moriya term, due to a change in the skew angle between two interacting magnetic moments. Keywords: magnetodielectric effect, phase transition, week ferromagnetism.
Crystal structure and thermodynamic properties of germanate CuEu-=SUB=-2-=/SUB=-Ge-=SUB=-2-=/SUB=-O-=SUB=-8-=/SUB=-
Authors: Denisova L. T.  , Molokeev M. S.  , Irtyugo L. A.  , Belousova N. V.  , Denisov V. M.
Published: January 2023

Copper-europium germanate CuEu2Ge2O8 was obtained from the initial CuO, Eu2O3 and GeO2 oxides using solid-phase synthesis by annealing in air in the temperature range of 1223-1273 K. Its crystal structure was determined (space group Cm). The influence of temperature on high-temperature heat capacity of the synthesized germanate was studied by the differential scanning calorimetry method. It was found that the dependence of heat capacity on temperature has an extreme value related to a phase transition. The thermodynamic properties were calculated based on the experimental data about heat capacity. Keywords: copper-europium germanate, solid-phase synthesis, crystal structure, thermodynamic properties.
A weak manifestation of the field effect in metal-dielectric-semiconductor structures with a ferroelectric insulating layer Ba-=SUB=-x-=/SUB=-Sr-=SUB=-1-x-=/SUB=-TiO-=SUB=-3-=/SUB=-
Authors: Belorusov D. A.  , Goldman E. I.  , Chucheva G. V.
Published: January 2023

High-frequency measurements of the capacitance and conductivity of Ni-Ba0.8Sr0.2TiO_3-Pt and Ni-Ba0.8Sr0.2TiO_3-Si objects with a ferroelectric thickness of 120 nm in the paraelectric phase were carried out. It is shown that in the entire range of external voltages, the electric field practically does not penetrate Si. The conclusion made earlier about the reasons for the weak manifestation of the field effect is confirmed --- the polarization of the ferroelectric layer is almost completely shielded by the charges of electronic traps at the Ba0.8Sr0.2TiO_3-Si contact. It is noted that a sharp decrease due to passivation of the activity of surface traps will allow implementing transistors based on metal-BST-Si structures with a working surface channel of non-basic charge carriers and will ensure the construction of high-quality FeRAM non-volatile memory cells. Keywords: metal-dielectric-semiconductor-structures, metal-dielectric-metal-structures, ferroelectric films of the composition Ba0.8Sr0.2TiO3, high-frequency impedance.