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Experimental study has been made of the ignition of a subcritical microwave discharge at pressures in the range 55–79 Torr with the initiation by pulsed laser radiation (58 mJ in a pulse). A rise of 36% in the critical pressure was obtained to form the discharge with the orientation of the laser beam along the vector of the microwave-field strength. Computer modeling has shown that upon the traversal of a focused laser beam, a highly conductive laser trail can be formed with a peak ionization degree as high as 10%, which, for a period of the order of 1 μs, locally enhances the electric microwave field up to supercritical values. [ABSTRACT FROM AUTHOR]

In this paper we carried out experimental study of a heat flux on the shocktube surface during passage of shock wave using a gradient sensor based on bismuth single crystal. The obtained experimental data were compared with numerical simulation results. It is shown that after passing through contact surface that separating the hot "plug" and pushing gas, the colder gas flow is mixed with the hot one. The heat transfer on the contact surface was evaluated. [ABSTRACT FROM AUTHOR]

The development and formation of X-ray crystallography of macromolecules, or protein crystallography, is one of the most important achievements of science in the 20th century. The possibility of establishing the three-dimensional structures of macromolecules of proteins and nucleic acids at atomic level has ensured the rapid development of molecular biology, biochemistry, bioengineering, and biotechnology and allowed researchers to reach the modern level of pharmacology. The review considers the results of studies of protein structures performed at the Shubnikov Institute of Crystallography of the Russian Academy of Sciences from the 1960s up to now. [ABSTRACT FROM AUTHOR]

The work is devoted to the study of high electron mobility transistor (HEMT) based on gallium nitride (GaN) in order to find the optimal composition and thickness of the buffer layer for the development of a power normally-off transistor with the highest possible breakdown voltage. The study was carried out using Sentaurus Device software (TCAD). The work shows the dependence of breakdown voltage on modifications made to the design. In particular, it has been established that to achieve breakdown voltages of the order of 1000 V, it is necessary to have an AlGaN buffer layer in GaN HEMT with a thickness of at least 4 µm, an aluminum mole fraction of about 5%, as well as doping with carbon or iron of the order of 1018 cm–3. Doping the AlGaN buffer layer with carbon (C) or iron (Fe) increased the potential barrier in the channel-buffer heterojunction, which led to an increase in the breakdown voltage of the HEMT. Increase the breakdown voltage to 900 V was possible by increasing concentration of C or Fe in the buffer layer from 1015 to 1017 cm–3. Breakdown voltage of the Fe-doped structure begins to exceed breakdown voltage of the C-doped structure, when impurity concentration continues to increase. The current-voltage characteristics of a С-doped transistor remain stable up to a concentration of 1019 cm–3 while the current in the conducting channel of a Fe-doped transistor decreases with increasing concentration. [ABSTRACT FROM AUTHOR]

In this paper, we report the preparation of high-purity 28Si silicon and 72Ge germanium isotopes and their volatile hydrides with controlled concentrations of the 29Si and 73Ge nonzero nuclear spin isotopes for producing Si/SiGe heterostructures for quantum computers employing the nuclear spin state as a qubit. We have prepared 28SiH4 and 28Si samples containing about 99.9, 99.99, and 99.999% 28Si as a major isotope and 340 ± 8, 41.1 ± 4.3, and 11.4 ± 0.1 ppm of the 29Si isotope. In addition, we obtained high-purity 72GeH4 and 72Ge samples containing about 99.9% 72Ge as a major isotope and 109.9 ± 9.6 ppm of the 73Ge isotope. [ABSTRACT FROM AUTHOR]

Searching for a specific inhibitor of pyrimidine nucleoside phosphorylase (PyNP) was a central objective of the work. The search was carried out by modeling protein–ligand complexes via molecular docking and molecular dynamics (MD), which make it possible to calculate the protein–ligand binding energy ΔGbind. The following compounds were selected as possible inhibitors: 2',3'-didehydro-3'-deoxythymidine (d4T), 1-(2-deoxy-2-fluoro-β-D-arabinofuranosyl)-5-ioduracil (fiauridine, FIAU), 1-(2-deoxy-2-fluoro-β-D-arabinofuranosyl)-5-uracil (FAU), and 2-pyrimidin-2-yl-1H-imidazole-4-carboxylic acid (PIA). A preliminary estimate of the binding energy was obtained by the linear interaction energy (LIE) method, and a more accurate calculation was carried out by the free energy perturbation (FEP) method in the GROMACS software package. The calculation results showed that PIA and d4T bind to the active site of Bacillus subtilis PyNP (BsPyNP) with higher affinities as compared with the other putative inhibitors. PIA binds less strongly to human thymidine phosphorylase (hTP). This was assumed to minimize the possible side effects of this compound used for therapeutic purposes. [ABSTRACT FROM AUTHOR]

The impurity composition of isotopically enriched germane 70GeH4 was studied for the first time by gas chromatography–mass spectrometry. Impurities were separated using capillary adsorption columns: GS-GasPro (60 m × 0.32 mm) packed with silica gel, GS-CarbonPLOT (25 m × 0.32 mm × 0.25 μm) packed with a carbon sorbent, and a column packed with poly(trimethylsilylpropyne) (25 m × 0.26 mm, df = 0.25 μm)). The use of these columns is shown to provide a high resolution of chromatographed substances. Impurities were identified by comparing their mass spectra with the data of the NIST library. Gases forming a part of the atmosphere, C1–C7 hydrocarbons, chlorine- and oxygen-containing hydrocarbons, sulfur-containing substances, and homologs and alkyl derivatives of germane were detected in germane. As a result of studying the composition of their mass spectra, the mass spectra of impurities 70GeC3H10 and 70GeC4H12, which are absent in the published sources, were obtained and described for the first time. The concentrations of impurities in high-purity germane, as well as their distribution over fractions isolated during the rectification purification of germane, were determined. The limits of detection of the identified substances were 2 ×10–7–1 × 10–4 mol %. [ABSTRACT FROM AUTHOR]

Single-crystal 70Ge germanium with high isotopic and chemical purity has been prepared by a hydride method. Germanium isotopes have been separated by centrifugation with the use of monogermane as a starting volatile substance. Isotopically enriched polycrystalline 70Ge has been prepared by pyrolyzing 70GeH4 monogermane. A 70Ge single crystal has been grown by the Czochralski technique. The resultant material has p-type conductivity and intrinsic resistivity at room temperature. The concentration of elemental impurities is under 10–6 to 10–5 wt %. The isotopic purity of the 70Ge single crystal is 99.926 at % and it contains a record low concentration of the odd isotope 73Ge: 0.00007 at %. [ABSTRACT FROM AUTHOR]

Uridine phosphorylases are known as key targets for the development of new anticancer and antiparasitic agents. Crystals of uridine phosphorylase from the pathogenic bacterium Vibrio cholerae were grown in microgravity by the capillary counter-diffusion method on board of the International Space Station. The three-dimensional structure of this enzyme was determined at atomic (1.04 Å) resolution (RCSB PDB ID: 6Z9Z). Alternative conformations of long fragments (β-strands and adjacent loops) of the protein molecule were found for the first time in the three-dimensional structure of uridine phosphorylase in the absence of specific bound ligands. Apparently, these alternative conformations are related to the enzyme function. Conformational analysis with Markov state models demonstrated that conformational rearrangements can occur in the ligand-free state of the enzyme. [ABSTRACT FROM AUTHOR]

The gradient heat flux sensor made of a bismuth single crystal is calibrated. The volt–watt sensitivity of the sensor is determined and the method of data processing based on the 1D heat conduction equation for a thin plate is proposed. This method is tested on experimental data obtained for the initiation of a laser discharge in a calm atmosphere and in a supersonic gas flow. [ABSTRACT FROM AUTHOR]

The high-resolution three-dimensional structure of uridine phosphorylase from the pathogenic bacterium Vibrio cholerae in complex with the competitive inhibitor 2,2'-anhydrouridine was determined by X-ray diffraction (RCSBPDB ID: 6RCA). The three-dimensional structure of this complex is compared with the previously determined structures of V. cholerae uridine phosphorylase in complex with the substrate (uridine) and S. typhimurium uridine phosphorylase in complex with 2,2'-anhydrouridine. The protein–inhibitor and protein–substrate binding free energies were calculated by the free-energy perturbation method. The number of stable hydrogen bonds between the 2,2'-anhydrouridine molecule and the active site of the enzyme is smaller and these bonds are longer compared to the natural substrate of the enzyme (uridine). However, calculations taking into account solvation energy of the molecule and the entropy effects showed that the binding of the inhibitor (2,2'-anhydrouridine) at the active site of the protein is energetically more favorable than the binding of the native substrate (uridine). These results may be useful in the design of new inhibitors with a higher selectivity for the binding sites of uridine phosphorylases. [ABSTRACT FROM AUTHOR]

A procedure is described for determining the isotopic composition of highly enriched silicon as elementary 28Si and initial 28SiF4 by a single collector double focusing sector field ICP MS over a wide range of isotope concentrations (more than 6 orders of magnitude). To expand the range of measured isotopic concentrations, the signals of the main and "impurity" isotopes were recorded in solutions of different concentrations. The determination of the matrix effects and mass discrimination factors was carried out using the isotopic dilution method. This procedure allowed us to reach the uncertainty of measuring the concentration of the main isotope of ten thousandths of a percent in enriching >99.999% on a high-resolution single-collector inductively coupled plasma mass spectrometer. [ABSTRACT FROM AUTHOR]

The formation dynamics of the parameters of a microwave discharge in air localized at electric field maxima created by a specially developed focusing system is investigated using numerical simulations within an extended hydrodynamic model. All main parameters of the microwave discharge plasma are determined. The results on neutral gas heating demonstrate good agreement with the earlier experimental results. [ABSTRACT FROM AUTHOR]

This paper examines sources of carbon impurities in polycrystalline monoisotopic 28Si prepared by a hydride method. Analytical data on the concentrations of carbon-containing impurities in volatile silicon compounds (28SiH4 and 28SiH4), process gases (Ar and H2), and polycrystalline 28Si are used to identify the major sources of carbon in the polycrystalline 28Si prepared by the hydride method. These are the starting 28SiH4 and calcium hydride used in 28SiH4 conversion into 28SiH4. The rate of carbon intake into polycrystalline silicon from the apparatus material during the monosilane pyrolysis process does not exceed 9 × 1011 cm-2 h-1. Polycrystalline silicon has been precipitated from monosilane with different concentrations of hydrocarbon impurities. At hydrocarbon concentrations in the range 10-4 to 10-3 mol %, the carbon concentration in the monosilane correlates with that in the silicon obtained from it. High-purity monosilane has been used to prepare polycrystalline 28Si samples with concentrations of carbon impurities in the range (0.8-2.3) × 1015 cm-3. Based on calculations of the carbon impurity distribution along the length of a zone-refined ingot, we examine the effect of the initial carbon concentration in the starting polycrystal on the yield of single-crystal monoisotopic 28Si. Requirements are formulated for the carbon concentration in polycrystalline 28Si which ensure a high yield of single crystals with parameters suitable for metrological applications. [ABSTRACT FROM AUTHOR]

The structure of bacterial uridine phosphorylase (UPh) belonging to the NP-I family in complex with 6-methyluracil was determined for the first time at 1.17 Å resolution. The structural features of bacterial UPh from the bacterium Vibrio cholerae (VchUPh) responsible for selectivity toward 6-methyluracil acting as a pseudosubstrate were revealed. The repulsion between the hydrophilic hydroxyl group of the active-site residue Thr93 of VchUPh and the hydrophobic methyl group of 6-methyluracil prevents the oxygen atom O4' of the ribose moiety and the phosphate oxygen atom O3P of ribose 1-phosphate from forming hydrogen bonds with OG1_Thr93, which are essential for the enzymatic reaction. This, apparently, makes VchUPh inactive in the enzymatic synthesis of 6-methyluridine from 6-methyluracil. Hence, Thr93 is the residue, the modification of which will allow VchUPh to catalyze the biotechnologically important synthesis of 6-methyluridine from 6-methyluracil. Taking into account high structural homology of the functionally significant regions of bacterial UPhs, this conclusion is also true for other bacterial UPhs. It was demonstrated that bacterial thymidine phosphorylases of the NP-II family cannot bind 6-methyluracil in a proper conformation required for the catalysis because of a close contact between the 6-methyl group and Phe210. [ABSTRACT FROM AUTHOR]

X-ray photoelectron spectroscopy (XPS) depth chemical and phase profiling of air-oxidized niobium nanofilms has been performed. It is found that oxide layer thicknesses depend on the initial thickness of the niobium nanofilm. The increase in thickness of the initial Nb nano-layer is due to increase in thickness of an oxidized layer. [ABSTRACT FROM AUTHOR]

Narrow atomically precise graphene nanoribbons hold great promise for electronic and optoelectronic applications, but the previously demonstrated nanoribbon-based devices typically suffer from low currents and mobilities. In this study, we explored the idea of lateral extension of graphene nanoribbons for improving their electrical conductivity. We started with a conventional chevron graphene nanoribbon, and designed its laterally extended variant. We synthesized these new graphene nanoribbons in solution and found that the lateral extension results in decrease of their electronic bandgap and improvement in the electrical conductivity of nanoribbon-based thin films. These films were employed in gas sensors and an electronic nose system, which showed improved responsivities to low molecular weight alcohols compared to similar sensors based on benchmark graphitic materials, such as graphene and reduced graphene oxide, and a reliable analyte recognition. This study shows the methodology for designing new atomically precise graphene nanoribbons with improved properties, their bottom-up synthesis, characterization, processing and implementation in electronic devices. [ABSTRACT FROM AUTHOR]

In many types of human tumor cells and infectious agents, the demand for pyrimidine nitrogen bases increases during the development of the disease, thus increasing the role of the enzyme uridine phosphorylase in metabolic processes. The rational use of uridine phosphorylase and its ligands in pharmaceutical and biotechnology industries requires knowledge of the structural basis for the substrate specificity of the target enzyme. This paper summarizes the results of the systematic study of the three-dimensional structure of uridine phosphorylase from the pathogenic bacterium Vibrio cholerae in complexes with substrates of enzymatic reactions-uridine, phosphate anion, thymidine, uracil, and thymine. These data, supplemented with the results of molecular modeling, were used to consider in detail the structural basis for the substrate specificity of uridine phosphorylases. It was shown for the first time that the formation of a hydrogen-bond network between the 2′-hydroxy group of uridine and atoms of the active-site residues of uridine phosphorylase leads to conformational changes of the ribose moiety of uridine, resulting in an increase in the reactivity of uridine compared to thymidine. Since the binding of thymidine to residues of uridine phosphorylase causes a smaller local strain of the β-N1-glycosidic bond in this the substrate compared to the uridine molecule, the β-N1-glycosidic bond in thymidine is more stable and less reactive than that in uridine. It was shown for the first time that the phosphate anion, which is the second substrate bound at the active site, interacts simultaneously with the residues of the β5-strand and the β1-strand through hydrogen bonding, thus securing the gate loop in a conformation [ABSTRACT FROM AUTHOR]

Pyrimidine nucleoside phosphorylases, which are widely used in the biotechnological production of nucleosides, have different substrate specificity for pyrimidine nucleosides. An interesting feature of these enzymes is that the three-dimensional structure of thymidine-specific nucleoside phosphorylase is similar to the structure of nonspecific pyrimidine nucleoside phosphorylase. The three-dimensional structures of thymidine phosphorylase from Salmonella typhimurium and nonspecific pyrimidine nucleoside phosphorylase from Bacillus subtilis in complexes with a sulfate anion were determined for the first time by X-ray crystallography. An analysis of the structural differences between these enzymes demonstrated that Lys108, which is involved in the phosphate binding in pyrimidine nucleoside phosphorylase, corresponds to Met111 in thymidine phosphorylases. This difference results in a decrease in the charge on one of the hydroxyl oxygens of the phosphate anion in thymidine phosphorylase and facilitates the catalysis through S2 nucleophilic substitution. Based on the results of X-ray crystallography, the virtual screening was performed for identifying a potent inhibitor (anticancer agent) of nonspecific pyrimidine nucleoside phosphorylase, which does not bind to thymidine phosphorylase. The molecular dynamics simulation revealed the stable binding of the discovered compound-2-pyrimidin-2-yl-1H-imidazole-4-carboxylic acid-to the active site of pyrimidine nucleoside phosphorylase. [ABSTRACT FROM AUTHOR]

This study is the first attempt to investigate the influence of severe plastic deformation (SPD) treatment on material surface behavior under intensive erosive conditions. Samples of aluminum alloy 1235 (99.3 Al) before and after high-pressure torsion (HPT) were subjected to intensive erosion by corundum particles accelerated via air flow in a small-scale wind tunnel. Velocity of particles varied from 40 to 200 m/s, while particle average diameter was around 100 μm. Surface roughness measurements provided possibility to compare surface properties of both materials after erosion tests. Moreover, SPD processing appeared to increase noticeably the threshold velocity of the surface damaging process. Additionally, structural analysis of the fracture surfaces of the tested samples was carried out. [ABSTRACT FROM AUTHOR]

Uridine phosphorylases play an essential role in the cellular metabolism of some antibacterial agents. Acute infectious diseases (bubonic plague, yersiniosis, pseudotuberculosis, etc., caused by bacteria of the genus Yersinia) are treated using both sulfanilamide medicines and antibiotics, including trimethoprim. The action of an antibiotic on a bacterial cell is determined primarily by the character of its interactions with cellular components, including those which are not targets (for example, with pyrimidine phosphorylases). This type of interaction should be taken into account in designing drugs. The three-dimensional structure of uridine phosphorylase from the bacterium Yersinia pseudotuberculosis ( YptUPh) with the free active site was determined for the first time by X-ray crystallography and refined at 1.40 Å resolution (DPI = 0.062 Å; ID PDB: 4OF4). The structure of the complex of YptUPh with the bacteriostatic drug trimethoprim was studied by molecular docking and molecular dynamics methods. The trimethoprim molecule was shown to be buffered by the enzyme YptUPh, resulting in a decrease in the efficiency of the treatment of infectious diseases caused by bacteria of the genus Yersinia with trimethoprim. [ABSTRACT FROM AUTHOR]

Pseudotuberculosis and bubonic plague are acute infectious diseases caused by the bacteria Yersinia pseudotuberculosis and Yersinia pestis. These diseases are treated, in particular, with trimethoprim and its modified analogues. However, uridine phosphorylases (pyrimidine nucleoside phosphorylases) that are present in bacterial cells neutralize the action of trimethoprim and its modified analogues on the cells. In order to reveal the character of the interaction of the drug with bacterial uridine phosphorylase, the atomic structure of the unligated molecule of uridine-specific pyrimidine nucleoside phosphorylase from Yersinia pseudotuberculosis ( YptUPh) was determined by X-ray diffraction at 1.7 Å resolution with high reliability ( R = 16.2, R = 19.4%; r.m.s.d. of bond lengths and bond angles are 0.006 Å and 1.005°, respectively; DPI = 0.107 Å). The atoms of the amino acid residues of the functionally important secondary-structure elements-the loop L9 and the helix H8-of the enzyme YptUPh were located. The three-dimensional structure of the complex of YptUPh with modified trimethoprim-referred to as 53I-was determined by the computer simulation. It was shown that 53I is a pseudosubstrate of uridine phosphorylases, and its pyrimidine-2,4-diamine group is located in the phosphate-binding site of the enzyme YptUPh. [ABSTRACT FROM AUTHOR]

The article discusses the study on the synthesis of monoisotopic 73GeH4 and 74GeH4 monogermanes with ≈99.9 percent isotope and chemical compounds' chemical elements of 10–5 mol %. The study involves monogermanes synthesis featuring their quantification of impurity composition and deep purification. Result shows that the content of impurities in the monogermanes does not surpass to 10–5 mol %.

Methods of calibrating secondary standard plasma radiators, based on the use of a synchrotron with an intense magnetic field, are developed, which enable problems of both vacuum coupling of the acceleration chamber and the plasma radiator to be solved, and also enable the degree of polarization of the synchronous radiation to be taken into account. It is shown that a comparison of the characteristics of the synchrotron radiation of the storage ring and of the electron synchrotron in the visible region using a telescope and cooled CCD matrix ensures that the relative synchrotron spectrum is absolute. [ABSTRACT FROM AUTHOR]

Endonucleases (EC 3.1) are enzymes of the hydrolase class that catalyze the hydrolytic cleavage of deoxyribonucleic and ribonucleic acids at any region of the polynucleotide chain. Endonucleases are widely used both in biotechnological processes and in veterinary medicine as antiviral agents. Medical applications of endonucleases in human cancer therapy hold promise. The results of X-ray diffraction studies of the spatial organization of endonucleases and their complexes and the mechanism of their action are analyzed and generalized. An analysis of the structural studies of this class of enzymes showed that the specific binding of enzymes to nucleic acids is characterized by interactions with nitrogen bases and the nucleotide backbone, whereas the nonspecific binding of enzymes is generally characterized by interactions only with the nucleic-acid backbone. It should be taken into account that the specificity can be modulated by metal ions and certain low-molecular-weight organic compounds. To test the hypotheses about specific and nonspecific nucleic-acid-binding proteins, it is necessary to perform additional studies of atomic-resolution three-dimensional structures of enzyme-nucleic-acid complexes by methods of structural biology. [ABSTRACT FROM AUTHOR]

Possibility of performing a mechanically activated synthesis of pure monosilane by the reaction of calcium hydride with silicon tetrafluoride in a rotating flow-through reactor containing milling bodies was analyzed. A number of operation parameters of the grinding reactor were theoretically evaluated and experimentally determined. [ABSTRACT FROM AUTHOR]

The three-dimensional structure of unligated laccase from Cerrena maxima was established by X-ray diffraction at 1.76-Å resolution; Rwork = 18.07%, Rfree = 21.71%, rmsd of bond lengths, bond angles, and chiral angles are 0.008 Å, 1.19°, and 0.077°, respectively. The coordinate error for the refined structure estimated from the Luzzati plot is 0.195 Å. The maximum average error in the atomic coordinates is 0.047 Å. A total of 99.4% of amino-acid residues of the polypeptide chain are in the most favorable, allowable, and accessible regions of the Ramachandran plot. The three-dimensional structures of the complexes of laccase from C. maxima with molecular oxygen and hydrogen peroxide were determined by the molecular simulation. These data provide insight into the structural aspect of the mechanism of the enzymatic cycle. The structure factors and the refined atomic coordinates were deposited in the Protein Data Bank (PDB-ID code is 3DIV). [ABSTRACT FROM AUTHOR]

The influence of severe plastic deformation on the material surface is investigated under highspeed erosion conditions. The AD1 aluminum alloy was tested with the structure changed by severe plastic torsional deformation. [ABSTRACT FROM AUTHOR]

The composition and contents of metallic impurities (in nonvolatile form) in isotopically unmodified and 76Ge-depleted germanium tetrafluoride samples were determined by chemical atomic emission spectrometry. The germanium tetrafluoride samples were then converted to germanium dioxide. The impurity compositions of the resultant germanium dioxide samples were determined by laser mass spectrometry, atomic emission spectrometry, inductively coupled plasma mass spectrometry, and spark source mass spectrometry. [ABSTRACT FROM AUTHOR]

The synthesis of silane by reacting silicon tetrafluoride and calcium hydride is shown to proceed as a propagating wave. The main parameters of the process, namely, the propagation velocity, the reaction front temperature, and calcium conversion, are determined. The mathematical model of wave propagation for an exothermic reaction in a porous medium with purging a gaseous oxidant describes qualitatively the major laws of the process. [ABSTRACT FROM AUTHOR]

Uridine phosphorylase ( UPh) belongs to pyrimidine nucleoside phosphorylases. This enzyme catalyzes cleavage of the C-N glycoside bond in uridine to form uracil and ribose-1’-phosphate. Uridine phosphorylase supplies cells with nucleotide precursors by catalyzing the phosphorolysis of purine and pyrimidine nucleosides. This is an alternative to de novo nucleotide synthesis. The three-dimensional structure of native uridine phosphorylase from Salmonella typhimurium ( StUPh) in a new crystal form was solved and refined at 1.90 Å resolution ( R st = 20.37%; R free = 24.69%; the rmsd of bond lengths and bond angles are 0.009 Å and 1.223°, respectively). A homodimer containing two asynchronously functioning active sites was demonstrated to be the minimum structural unit necessary for function of the hexameric StUPh molecule ( L 33 L 2). Each active site is formed by amino acid residues of both subunits. [ABSTRACT FROM AUTHOR]

A mathematical model of heat and mass transfer in vacuum oscillating drying of lumber in which the drying process is made up of alternating stages of warming up and vacuum treatment has been developed. At the stage of warming up, it has been proposed to use a superheated steam to intensify heat and mass transfer processes and to relax stresses occurring at the stage of vacuum treatment. [ABSTRACT FROM AUTHOR]

An Erratum to this paper has been published: https://doi.org/10.1134/S1063774521070270 [ABSTRACT FROM AUTHOR]

A method of producing refractories from Kovdor deposit natural baddeleyite concentrate, with the use of natural grain-size powders (less than 0.5 mm) obtained after concentration of the residues of iron ore concentrate, has been developed. To obtain parts of natural baddeleyite by combining stabilization with firing, it is necessary to add previously synthesized calcium zirconate as a stabilizing addition and a firing addition of AlO to improve firing and increase the strength properties. The production of sectors of natural grain-size baddeleyite has been introduced at the Borovichi Refractory Combine. Such parts have found use as the thermal insulation lining of continuous furnaces with a service temperature on the refractory surface of 2000°C. [ABSTRACT FROM AUTHOR]

It was found that the North-Onezhsk bauxites are promising raw materials for the production of highly resistant ladle bricks. We developed and mastered a technology in the BKO conditions for making ladle brick using these bauxites containing up to 6% iron oxides. In the lining of the steel ladles made with the use of bauxite chamotte, the bricks wear out 30-40% less than with ordinary ladle brick produced by BKO and the Chasov Yarsk Combine. [ABSTRACT FROM AUTHOR]

The results of measurements of the drag of axisymmetric bodies with smooth and ribbed central cylindrical sections and affinely similar trailing edges of various lengths are given. The experimental data were obtained for zero angle of attack and the numbers M=0.25–0.85 and Re=107–2.4·107 (calculated on the basis of the length of the body without the trailing section). The trailing-edge flow separation was visualized by the oil film method. It is shown that ribbing can lead to a decrease in drag due not only to a reduction in turbulent friction but also to reduction of the separation zone on the smooth trailing section of the body. [ABSTRACT FROM AUTHOR]

Sensitized photooxidation of a series of compounds with an anthracene structure in a block poly(methyl methacrylate) (PMMA) containing a tetrapyrrole pigment (TPP) or anthraquinone dyes as spectral sensitizers, was studied. The values of changes in the molar refraction at λ equal to 441 and 633 nm were determined experimentally. They satisfactorily agreed with the theoretical values calculated from dispersional relationships. The initial quantum yields of the photooxidation (ϕox) of the anthracene compounds were measured both in solution and in PMMA blocks. The lack of correlation between the ϕox values in the solid polymers and in the liquid solution indicates the dominating role of the polymeric matrix in determining the effectiveness of photooxidation process taking place. In the selection of the optimal polymerization conditions for the synthesis of the polymeric blocks, the values of ϕox of certain anthracene compounds can be up to 1. In the series of the anthraquinone dyes used, 1,4-dihydroxy and 2-aminoanthraquinones, whose ϕox reaches the values of 0.2-0.25 have the highest sensitizing ability. [ABSTRACT FROM AUTHOR]

Hydrocarbon impurities in silicon tetrafluoride originate from the sodium hexafluorosilicate used as a precursor for the preparation of SiF through the thermal decomposition of NaSiF. We have studied the fraction of C-C hydrocarbons released as a function of temperature during the thermal decomposition of sodium hexafluorosilicate. The lighter hydrocarbons-methane, ethane, and ethylene-are shown to be released at lower temperatures. One source of hydrocarbon impurities in sodium hexafluorosilicate is the sodium carbonate used to prepare it. [ABSTRACT FROM AUTHOR]

The possibility of the reduction of hexafluorodisiloxane by calcium hydride in the synthesis of silane from silicon tetrafluoride has been studied. This reaction is shown to be not decisive for oxygen contamination of silane. The most likely reason for the appearance of impurity SiOH in 'fluoride' silane is the Ca(OH)-catalyzed reaction of silane with trace water. The concentration of impurity SiOH in silane at the stage of synthesis may be efficiently decreased by the preliminary purging of calcium hydride with a hydrogen (grade A) flow. [ABSTRACT FROM AUTHOR]

The article focuses on a study carried out to produce and purify silanes, 29SiH4 and 30SiH4, of high isotopic and chemical purity. It states that higher chemical purity with a higher content of the main isotope are required to study the chemical properties of silanes. It describes how the silanes were analyzed by gas chromatography method and the isotopic composition of silanes was determined by laser mass spectrometry.