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Concrete is a quasi-brittle building material that has low tensile strength. The process of its destruction under loading is inhomogeneous, due to the nature of the concrete structure mass, consisting of components with different physical and mechanical properties. Gradual deformation and destruction can be characterized as a process of formation and development of microcracks. The presence of different-sized components in concrete makes it possible to consider its structure as a multi-level system. In this system, each level is a matrix with its own structural inclusions, which play both a structure-forming role and the role of stress concentrators under the action of mechanical loads. The critical stress intensity factor is a good indicator of the crack resistance (fracture toughness) of a material. Nanoconcrete, from the point of view of a multilevel system, is a concrete composite with crack propagation inhibitors at the level of the cementing substance (carbon nanotubes are consi-dered as inhibitors). The presence of fiber fibers at subsequent scale levels allows us to consider concrete as a composite with multi-level dispersed reinforcement (nanofiber concrete). The paper discusses the change of concrete fracture toughness indicator (crack resistance) with dispersed reinforcement of the matrix at different structural levels. The presented for normal separation of notched cubes under eccentric compression with the determination of the stress intensity factor for concrete modified with carbon nanotubes acting as crack propagation inhibitors at the level of cementing substance (nanoconcrete), as well as for nanofiber concrete with dispersed reinforcement at the level of fine-grained concrete. Based on experimental studies by non-equilibrium methods of fracture mechanics, compositions of nanofiber-reinforced concrete of maximum crack resistance (fracture toughness) with different fiber concentrations and several types of matrices modified with nanocarbon additives are proposed in the paper.

The most common and reliable material without which modern construction is indispensable is concrete. The development of construction production is pushing for new solutions to improve the quality of concrete mix and concrete. The most demanded and significant indicators of a concrete mixture are the compressive strength and mobility of the concrete mixture. Every year, the volume of research on nanomaterials as modifying components of concrete is significantly increasing, and the results indicate the prospects for their use. Nanoparticles with a large specific surface are distinguished by chemical activity, can accelerate hydration and increase strength characteristics due to nucleation and subsequent formation of C–S–H and compaction of the material microstructure. Sol of nanosilica, which can be used instead of microsilica from industrial enterprises, and carbon nanomaterial have a wide reproduction base. This paper presents studies of these types of nanomaterials and the results of their application in cement concrete. Studies have shown that the effect is also observed with the introduction of an additive containing only one type of nanoparticles. The dependence of the obtained characteristics of cement concretes on the content of these nanomaterials has been established. It has been found that the best results were obtained with an additive in which the above-mentioned nanomaterials were used together. Compressive strength of heavy concrete samples, improved by the complex nanodispersed system, was 78.7 MPa, which exceeds the strength of the sample containing the CNT additive in a pair with a super-plasticizer by 37 %. The paper proposes the mechanism for action of the presented complex additive.

Using the statistical data for 2004-2018, the dynamics of forest fires and the number of hunting and fishing fauna in Irkutsk region and in one of its specially protected natural area - Olkhon district as part of the Baikal national Park were studied. Against the background of the positive dynamics of forest fire indicators, the dependence of the number of animals on their family, species and fires in adjacent areas and the region as a whole was established. The linear correlations confirmed the positive impact of fires on the population of deer (Cervidae), canids (Canidae), cats (Felidae), bears (Ursidae) and pheasants (Phasianidae), determined by the migration of animals from mountainous areas. The unstable and negative population dynamics was revealed for the Kunya family (Mustelidae).

Deep oxidation of hydrocarbons over platinum catalysts underlies the majority of processes for purification of industrial waste gases. Since waste gases usually contain carbon monoxide, it is important to investigate its effect on the oxidation kinetics of hydrocarbons. This paper considers results of the study on the oxidation kinetics of propane over a glass fiber platinum catalyst in the presence or absence of CO in the reaction mixture. It was found that at low temperatures the presence of CO strongly hinders the oxidation of propane, whereas upon temperature elevation this detrimental effect is replaced by the beneficial effect of CO. As shown by numerical modeling, this bidirectional effect can be attributed to the competitive adsorption of oxygen, propane and CO on the catalyst active sites.

A number of historical anecdotes about the great Russian commander Alexander Vasilyevich Suvorov are considered in the article. Attention is focused on the fact that many of the named sources are not supported by documents, but are actively used by some authors when creating the biography of A. V. Suvorov. It is shown in the article that over time, the narratives built on the basis of historical anecdotes have undergone significant changes, they help reconstruct the key moments of the commander’s life and characterize his personality traits.

Results of testing nanofibrous-concrete test beams for axial tensile strength, for cleavage tensile strength, and for compressive strength have been given. Concrete matrices covering a broad spectrum of compressive-strength classes of concretes of construction grade were used as a basis. A macrolevel fiber (steel or polymeric) or a nanolevel fiber (carbon nanotubes) was made part of a concrete matrix. An increase of 80% in the axial tensile strength and of 145% in the cleavage tensile strength was recorded in the nanofibrous-concrete test pieces. Diagrams of axial tensile straining of the test pieces have been obtained.

Concrete is the most commonly used building material worldwide. One of its main disadvantages is the fragility of fracture and low crack resistance. The use of dispersed reinforcement of concrete composites is a promising direction in solving this type of problem. Dispersed fibers, evenly distributed over the entire volume of the material, create a spatial frame and contribute to the inhibition of developing cracks under the action of destructive forces. In order to increase the fracture toughness of concrete, dispersed fiber reinforcement is increasingly used in practice. The beginning of crack nucleation occurs at the nanoscale in the cement matrix. Thus, the use of nano-reinforcement with dispersed nanofibers can have a positive effect on the crack resistance of the cement composite. It is proposed to consider carbon nanotubes as such nanofibers. The presence of carbon nanofibers changes the microstructure and nanostructure of cement modified with carbon nanotubes. The result of the processes occurring in capillaries and cracks are deformations in the intergranular matrix, the free flow of which is prevented by rigid clinker grains and nanocarbon tubes, which creates a certain stress intensity at the tips of the separation cracks. The working hypothesis is confirmed that the required fracture toughness of structural concrete is provided by multi-level reinforcement: at the level of the crystalline aggregate of cement stone – carbon nanotubes, and at the level of fine-grained concrete – various macro-sized fibers (steel, polymer). Reinforcement of a crystalline joint with carbon nanotubes leads to an increase in the fracture toughness of the matrix (cement stone) by 20 %, compressive strength by 12 %, and tensile strength in bending by 20 %. When reinforcing at the level of fine-grained concrete, we obtain a composite – nanofibre-reinforced concrete with fracture toughness.

The tolerance factor is a good criterion to understand the structural transitions in Ln

The effects of temperature, time, and the composition of the solvent (water, HCl) on the processes of leaching of Na, Al, and Ca from sodium aluminosilicate fiberglass materials and also the physicochemical properties of the leached products were studied by inductively coupled plasma atomic emission spectroscopy, differentiating dissolution, and IR spectroscopy. It was found that, in water and aqueous HCl solutions, the process is dominated by the extraction of sodium from the glass because of the ion exchange of Na+ for H+. The Na leaching rate in H2O is limited by the ion-exchange rate on the glass fiber surface, and that in HCl is controlled by the Na diffusion in the bulk of the glass fiber. The structure of the leached glass fibers is formed by alternate sheets of several silicon–oxygen tetrahedra separated by narrow voids, which contain a considerable amount of molecular water and SiOH groups, characterized by the band of stretching vibrations of OH (ν = 3640 cm–1). In annealing, SiOH groups condense to release water; however, the ion-exchange properties of the fibers are partially conserved.

Samples of SO4/ZrO2/Al2O3 and Pt/Al2O3 Pt/Al2O3 catalysts and their physical mixtures are prepared, and the catalytic properties of the samples in n-hexane isomerization are studied. The considerable effect of the state of platinum on the catalytic performance of the samples is revealed. IR spectroscopy (COads), oxygen chemisorption, and oxygen-hydrogen titration show that the reduced catalysts contain ionic forms of platinum capable of adsorbing up to three hydrogen atoms per each surface atom of platinum. By means of H/D isotopic exchange, it is found that specific properties of ionic platinum are apparent in the formation of the hydride form of adsorbed hydrogen. It is speculated that the activity and stability of catalysts based on sulfated zirconia in n-hexane isomerization can be attributed to the involvement of ionic and metallic platinum in the activation of hydrogen. The results can be used to develop effective catalysts for the isomerization of C5–C6 gasoline fractions in order to obtain the isomerizate as a high-octane additive for modern gasolines.

Several composites were prepared by mechanochemical activation of the mixture of well-crystallized LaFeO3 and CeO2 (La:Ce = 0.1, 0.8), including following calcination at 900 °C, and characterized by means of XRD, XPS, HRTEM, EDX and UV–Vis DRS. Their tests as catalysts for N2O decomposition and CH4 oxidation at 700–900 °C showed non-additively high activity of calcined composites in both reactions. 16O/18O exchange was performed at 800 °C in LaFeO3, CeO2 and two composites (both calcined and non-calcined, La:Ce = 0.1) representing mainly unmodified CeO2 core covered by the finely dispersed LaFeO3, La and Fe oxides penetrating near surface layers of fluorite lattice. Namely calcined composite revealed the highest rate of oxygen transfer in the two-phase system “O 2 gas –surface–catalyst bulk” due to prominent increase of the rate of heteroexchange on the modified CeO2 surface at keeping unchanged the highest bulk oxygen mobility characterizing CeO2 that explained its activity in the reactions with oxygen participation.

This article is an attempt to elucidate the role of lattice oxygen mobility in catalytic activity of Sr-substituted ferrites at high temperatures. For this goal, three catalysts with close element (La, Sr, Fe) content but different phases and surface compositions: LaSrFeO 4 (surface)–La 0.4 Sr 0.6 FeO 3 ( LSF-N ), La 0.15 Sr 0.85 FeO 3 –La 0.7 Sr 0.3 FeO 3 ( LSF-C ) and LaSrFeO 4 have been studied in high temperature reactions of N 2 O decomposition, ammonia oxidation and methane combustion. The kinetics of 18 O/ 16 O oxygen exchange have been analyzed at 800 °C and 0.005 atm oxygen partial pressure, which is closely corresponding to the reaction conditions, and the rates of surface oxygen exchange and the coefficient of lattice oxygen diffusion have been evaluated. It allowed us to reveal the direct correlation between the surface exchange rate constant and the rate of N 2 O decomposition. For NH 3 oxidation, evidence of the same order of the samples activity both in surface oxygen exchange and ammonia oxidation reaction was shown. In methane oxidation it was found that activity correlates with the rate of exchange for 20 monolayers of oxygen atoms indicating the growing influence of lattice oxygen mobility. The results show that improvement of catalytic properties can be achieved when synthesizing “LaSrFeO 4 (surface)–La 0.4 Sr 0.6 FeO 3 ” composites. Such composites exhibit increased rate of surface oxygen exchange on retention of high lattice oxygen mobility, which can be attributed to formation of heterostructured interfaces.

Aim - to justify the use of custom-made ocular prostheses aimed at better functional and cosmetic outcomes.Cosmetic outcomes in 520 patients operated for either anophthalmia (89.1%), or ocular subatrophy (6.7%), or congenital micro-/anophthalmia have been analyzed. General and ophthalmic assessment was performed.Relationships were investigated between the results obtained in a particular patient, on the one hand, and primary etiology in his/her case, eye removal technique, postoperative management details, complications, treatments, and preventive measures, on the other. It has been found that, if aiming to avoid the development of anophthalmic syndrome, the choice of surgical technique should be done most carefully so that a muscle stump could be formed and primary prosthesis inserted. Indications for the use of complexly shaped ocular prostheses have been identified. We have also explored the possibilities for correction of cosmetic defects associated with the use of modified stock prostheses. Moreover, in this article particular attention is paid to the importance of cooperation between the oculoplastic surgeon and the ocularist in order to ensure timely orbital reconstruction.Indications for the use of custom-made ocular prostheses of complex shapes have been identified. The range of complications that may arise from their irrational use are discussed.Цель - обосновать использование индивидуальных форм протезов в целях повышения эффективности функционально-косметических результатов глазопротезирования. Материал и методы. Проведен анализ косметических результатов глазопротезирования у 520 пациентов, из них с анофтальмом - 89,1%, субатрофией глаза - 6,7%, врожденным микро- и анофтальмом - 4,2%. Использовались традиционные и специальные офтальмологические методы исследования. Результаты. Изучили взаимосвязь и зависимость полученных результатов от этиологии первичной патологии, характера оперативного вмешательства при удалении глаза, особенностей послеоперационной тактики ведения больных и развившихся осложнений, мероприятий по их профилактике и коррекции. Установлено, что ведущая роль в профилактике развития анофтальмического синдрома принадлежит выбору рационального метода операции с формированием объемной опорно-двигательной культи и адекватному первичному протезированию. Определены показания к использованию протезов сложных форм и возможности коррекции некоторых косметических недостатков при модификации изделий стандартных разновидностей. Акцентировано внимание на необходимости контакта между хирургом-офтальмопластиком и протезистом для своевременного проведения реконструктивных вмешательств в зоне орбиты. Заключение. Обоснованы показания к использованию протезов сложных индивидуальных форм и отражен характер осложнений, обусловленных их иррациональным применением.

Study of the dynamics of isotope transfer under steady state reaction conditions, the so called steady state isotopic transient kinetic analysis ( SSITKA ), is successfully employed in the investigation of different physical and chemical processes that occur on the surface of solids and in their lattice. The theoretical basis of SSITKA was initially developed and used to study the mechanism of catalytic reactions [1 – 4] . SSITKA applications were later extended to the reactions complicated by mass transfer processes as well as for the characterization of the catalyst acidity. Such a technique is based on the analysis of the isotope responses that result from the stepwise change of isotopic composition of the feed gas at equilibrium. Whereas most of methods used for the identifi cation of reaction intermediates or catalyst characterization operate at low temperature and pressure, such measurements can be performed in the conditions of interest that successfully solves the well known problems associated with “ pressure and temperature gaps. ” Therefore, the reliability of measured characteristics is substantially increased. This chapter includes a discussion of the general principles of SSITKA as well as the experimental and theoretical approaches that are used to study the isotopic transient kinetics, reactions of label transfer as applied to the problem to be solved. The dynamic features of the experimental setup that includes the stepwise disturbing system of feed gas fl ows, catalytic reactors, and mass spectrometric analysis are considered in detail. As a result, the reactor and mass spectrometers that are most convenient for dynamic isotopic studies were selected. The theoretical study of isotopic transient kinetics allowed for the separation of fi ve basic reaction pathways, which serve as elementary “ bricks ” to build virtually any reaction mechanism. It is shown that the key features of the reaction mechanism can be revealed directly from the shape of isotope response curves, while the detailed characteristics can be derived from numerical modeling by fi tting the experimental data with calculated ones. By the example of various catalytic reactions (ethylene epoxidation over Ag, deNOx with methane on Co ZSM 5, Fischer – Tropsch synthesis over Co based systems), we show how the reaction mechanism was revealed and the concentrations of key intermediates and reaction rate coeffi cients were estimated using different isotope labels ( 18 O, 15 N, 13 C, etc.). A single instance of transient isotopic kinetic study for the evaluation of mass transfer parameters of NO and water diffusion into the bulk of Pt containing fi berglass catalyst is discussed. Our experience helped to elucidate the mechanism of oxygen transport in oxides with perovskite and fl uorite lattice at high temperatures (up to 900 ° C). All kinetic parameters including the diffusion coeffi cients were obtained. The probability of H/D exchange for the quantifi cation of Br o nsted acidity in fi berglass materials is also discussed.

Radically different dependences of the activity of La1 − xSrxMnO3 (x = 0−0.5) perovskites in methane oxidation on the degree of substitution of strontium for lanthanum are observed for low and high temperatures. Unsubstituted LaMnO3 exhibits the highest activity in the temperature range from 300 to 500°C, while the sample with the maximum degree of substitution (La0.5Sr0.5MnO3) shows the highest activity at higher temperatures of 700–900°C. In the low temperature region, the activity of La1t - xSrxMnO3 is determined by the amount of weakly bound (overstoichiometric) oxygen, which is formed in cation-deficient lattices and is characterized by a thermal desorption peak with Tmax = 705°C. At higher temperatures (800–900°C), the strongly bound oxygen of the catalyst lattice is involved in the formation of the reaction products under both unsteady- and steady-state conditions. As a consequence, the catalytic activity in methane oxidation correlates with the apparent rate constant of oxygen diffusion in the oxide bulk.

The work presents the results of studying the mechanism of oxygen transport for a new promising class of oxygen-containing electrolytes based on lanthanum silicate with an apatite structure using impedance spectroscopy and isotopic oxygen heteroexchange. At 1000 K, in the case of samples with an optimum composition including codoped Fe and Al, σ ∼ 3 × 10−3 to 10−2 S/cm and D* reaches ∼10−8 cm2/s, which is close to the values of YSZ and Ce0.9Gd0.1O2 − δ (GDC). Lower energies of conductivity activation and oxygen diffusion for doped apatites (∼0.5–0.8 eV instead of ∼1 eV for GDC) and also equivalence as regards exchange of all oxygen atoms within apatite agree with the model, in which oxygen mobility is determined by a nonlinear cooperative migration process of oxygen atoms with fast exchange between interstitial and regular sites.

Results are given for testing the strength of formed elliptical dishes of titanium grade VT1-0 with thinning to 44% in the transition area. It is concluded from tests that thinning to 20% in the transition area does not affect the dish strength as a whole.

The kinetics of hydrogen isotopic exchange over fiberglass materials and reference samples (SiO 2 , H 3 PO 4 /SiO 2 , and HZSM-5) was studied at 500 °C under the dynamic adsorption–desorption equilibrium. The concentrations and H/D-exchange rates of different Bronsted acid sites (BAS) were determined using the numerical modeling of isotope exchange dynamics. The correlation between H/D-exchange rate of reference samples and their acidity determined by FTIR spectroscopy of adsorbed CO was established. Based on this correlation, the strength of BAS in fiberglass materials was shown to be comparable to that of HZSM-5 zeolite.

The dynamics of 18O isotope exchange between NO or H2O and a catalyst and the dynamics of 18O label transfer from NO to H2O have been studied under conditions of sorption-desorption equilibrium. The occurrence of a reaction of oxygen exchange between NO and water sorbed in the bulk of the catalyst was detected. This reaction occurs at platinum sites with the participation of acid sites of the glass matrix. The rate constants of the reaction of NO with platinum sites and the diffusion coefficients of water in the bulk of the glass matrix are evaluated.

The dynamics of 13 C transfer from methane to carbon dioxide was studied under the steady-state reaction conditions of selective NO reduction with methane on a CoZSM-5 catalyst at various reactant (NO, CH 4 , and O 2 ) concentrations and temperatures. It was found that the reaction occurs by a two-pathway mech- anism with the participation of Co 2+ sites (or CoO x clusters) and paired Co 2+ -OH sites localized at the boundary between the clusters and the zeolite; in this case, the rate of the reaction at boundary sites was higher by more than one order of magnitude. Based on the numerical simulation of isotopic response curves, the concentrations of intermediate compounds and the rate constants of particular steps were evaluated; differences in the kinetics via the above reaction pathways were found and analyzed.

The problem of the motion of the cathode spot of a vacuum arc electrical discharge in a magnetic field applied tangential to the cathode surface is considered. The treatment is based on concepts of the nonstationary, cyclical nature of processes occurring in the cathode spot and the key role of return electrons falling out of the near-cathode plasma back onto the cathode.

In accordance with structural data and numerical analysis of relaxation curves, a detailed scheme for the reaction of o-xylene oxidation is suggested.

Diffusion and solubility coefficients of O2, SO2 and SO3 in the active component of vanadium catalysts have been determined by a high-speed relaxation method. Processes of their dissolution are shown to be quasi-equilibrium with respect to catalytic reactions.

Based on numerical analysis of experimental data, the main ideas of the reaction mechanism have been confirmed and kinetic principles of the non-steady=state reaction have been determined.

An investigation of the energy spectra of the ions of a moving plasma enables one to determine a number of important plasma characteristics, such as the energy of directed motion of a plasma blob, the ion temperature, the plasma potential, the ion density and, very important, to estimate the percentage content of impurity ions in the plasma. The analysis of the measured energy spectra is considered for two cases: (1) An isotropic energy distribution of the ions in the centre of mass system of a plasma blob. (2) An anisotropic ion distribution with T/sub /// not=Tperpendicular to , which can occur for high velocity plasma blobs, when the formation time and the time of flight are less than tau ii.