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In the paper, nanocomposites based on diisopropylammonium iodide (DIPAI.) and Al2O3 nanoparticles (sized 100 nm) have been synthesized with varying a volume fraction of the latter (0.05, 0.10, 0.20). Temperature dependences of the permittivity and a signal of differential thermal analysis of the samples (in the range of 300 – 400 K) were studied in heating and cooling modes. Their infrared spectra were recorded at room temperature as well. An analysis of the measured temperature dependences indicated a change in the sequence of phase transitions in nanocomposites compared with the pure DIPAI. The totality of the results obtained allowed us to conclude that a change in hydrogen bonds with the participation of amino groups manifested itself in the nanocomposite structure took place. This can lead to the appearance of a ferroelectric state in the DIPAI.

In order to make material with improved properties, nanocomposites based on nanoporous Al2O3 films (having different pore sizes) filled with ferroelectric, namely, caesium nitrate CsNO3, have been fabricated, and their electrophysical charactistics have been investigated. The film surfaces were tested by electron microscopy. Temperature dependences of the effective permittivity ε' and of the third harmonic coefficient were measured for the nanocomposites. The phase-transition points were determined by the maximum value of the dε'/dT derivative. The reduction in pore was found to lead to a decrease in the Curie temperature (by more than 30 K) and a phase transition blur. This phenomenon is associated with the influence of intrinsic size effects.

The paper proposes an iterative method for finding the natural frequencies of symmetric oscillations for a rectangular CFCF plate using two hyperbolic-trigonometric series in two coordinates. In this case, a resolving homogeneous infinite system of linear equations which contains the desired natural frequency as a parameter has been obtained. Instead of deriving and solving the frequency equation, it was proposed to use the sequential search for the desired frequency values (the "shooting method") in combination with the method of successive approximations. Numerical results were found for the first three symmetric eigenforms. The influence of the number of series terms and the number of iterations on the accuracy of the results was investigated. The obtained results were compared with those of other authors and the published experimental data.

In the paper, the temperature dependences of the differential thermal analysis signal, permittivity, and amplitude of the third harmonic of the (KNO3)1–х/Snx composites have been studied. It was shown that the temperature of the α → β phase transition decreased by 2 – 3 K in the potassium nitrates being parts of the composites, and the temperature of the γ → α phase transition decreased up to 360 K. This result can be explained within the framework of the Landau – Ginzburg theory, taking into account the shielding of potassium nitrate particles by tin metal particles.

Some samples of the (KNO3)1–х/(CsNO3)x composite with different x values have been prepared, and their temperature dependences of the differential thermal analysis signal, of the dielectric constant, and the amplitude of the third harmonic (to find an existence domain of the polar phase) were studied. The sample surfaces were investigated by scanning electron microscopy. An increase in the proportion of CsNO3 was revealed to lead to a decrease in the coefficient of nonlinearity of the composite and to narrowing of the existence domain’s temperature range of the KNO3 ferroelectric phase III. Also it was found that the composite properties nonlinearity at x beyond 0.5 was determined by the CsNO3 properties.

The paper presents the results of studies of the linear and nonlinear dielectric properties of (R) -3-quinuclidinol embedded in porous aluminum oxide with a pore size of 300 nm, in comparison with the properties of bulk (R) -3-quinuclidinol. A decrease in the Curie temperature in the nanocomposite, both upon heating and cooling, in comparison with a bulk sample is revealed. A decrease in the phase transition temperature can be interpreted on the basis of known theoretical models for ferroelectric small particles.

The paper presents the results of studies of the dielectric properties of (DIPAC)1-x/(PbTiO3)x composites with a volume fraction of lead titanate in composite x from 0.10 to 0.40. It was shown that the addition of lead titanate to diisopropylammonium chloride leads to an increase in the dielectric constant and the appearance of additional phase transitions during heating and cooling. The appearance of a new phase transition is explained in the framework of the Landau-Ginzburg theory, taking into account the dipole-dipole interaction between the components.

The results of a study of linear and nonlinear dielectric properties, as well as calorimetric measurements of a ferroelectric composite (C6H16NBr)1-x/(PbTiO3)x with a volume fraction of lead titanate particles in a composite x = 0.1, 0.2, 0.3, are presented. It was shown that the addi-tion of lead titanate particles to diisopropylammonium bromide leads to a change in the sequence of structural phase transitions in diisopropylammonium bromide, an increase in the effective di-electric constant and tanδ. In the temperature range of 150-138 ° C, there are two C6H16NBr phases (ferroelectric P21 and non-ferroelectric P212121), the ratio of which depends on the frac-tion of lead titanate particles in the composite.

The problem of cantilever plate stability has been little studied due to the difficulty of solving the corresponding boundary problem. The known approximate solutions mainly concern only the first critical load. In this paper, stability of an elastic rectangular cantilever plate under the action of uniform pressure applied to its edge opposite to the clamped edge is investigated. Under such conditions, thin canopies of buildings made of new materials can be found at sharp gusts of wind in longitudinal direction. At present, cantilever nanoplates are widely used as key components of sensors to create nanoscale transistors where they are exposed to magnetic fields in the plate plane. The aim of the study is to obtain the critical force spectrum and corresponding forms of supercritical equilibrium. The deflection function is selected as a sum of two hyperbolic trigonometric series with adding special compensating summands to the main symmetric solution for the free terms of the decomposition of the functions in the Fourier series by cosines. The fulfillment of all conditions of the boundary problem leads to an infinite homogeneous system of linear algebraic equations with regard to unknown series coefficients. The task of the study is to create a numerical algorithm that allows finding eigenvalues of the resolving system with high accuracy. The search for critical loads (eigenvalues) giving a nontrivial solution of this system is carried out by brute force search of compressive load value in combination with the method of sequential approximations. For the plates with different side ratios, the spectrum of the first three critical loads is obtained, at which new forms of equilibrium emerge. An antisymmetric solution is obtained and studied. 3D images of the corresponding forms are presented.

The process of thermocatalytic conversion of pine ethanol lignin in supercritical ethanol was studied over NiCu/SiO2 and NiCuMo/SiO2 catalysts bearing 8.8 and 11.7 wt.% of Mo. The structure and composition of ethanol lignin and the products of its thermocatalytic conversion were characterized via 2D-HSQC NMR spectroscopy, GC-MC. The main aromatic monomers among the liquid products of ethanol lignin conversion were alkyl derivatives of guaiacol (propyl guaiacol, ethyl guaiacol and methyl guaiacol). The total of the monomers yield in this case was 12.1 wt.%. The temperature elevation up to 350 °C led to a slight decrease in the yield (to 11.8 wt.%) and a change in the composition of monomeric compounds. Alkyl derivatives of pyrocatechol, phenol and benzene were observed to form due to deoxygenation processes. The ratio of the yields of these compounds depended on the catalyst, namely, on the content of Mo in the catalyst composition. Thus, the distribution of monomeric compounds used in various industries can be controlled by varying the catalyst composition and the process conditions. [ABSTRACT FROM AUTHOR]

The present work reports the experimental results of studying linear and nonlinear dielectric properties of a ferroelectric nanocomposite from RbNO3 embedded in pores of an Al2O3 matrix. The dielectric relaxation times were determined above and below the phase transition temperature of pure RbNO3 (436 K). It was shown that for RbNO3 incorporated into nanosized pores of the Al2O3 matrix, a decrease in the phase transition temperature and a change in relaxation times were observed. [ABSTRACT FROM AUTHOR]

Shapes of a square Kirchhoff plate with a clamped edge are obtained and analyzed, before and after losing stability in the case of a compound bending (uniform transverse loading in combination with edge compressive loading), as well as equilibrium forms and critical loadings only with clamping in the plate’s surface. Hyperbolic trigonometric series are used for solving. It was established that transverse loading causing small deformations does not affect the plate’s stability. The range of the critical state corresponds with an unlimited increase in bends of interior points of a plate. As critical loading, we suggest taking the one at which the bends at the plate’s center tend to infinity the most rapidly. As balanced loading, we suggest taking the one at which the plate acquires a new stable equilibrium form. A range of critical and balanced loadings of a square plate with a clamped edge was presented. The corresponding 3D forms of supercritical equilibrium of the given plate were obtained. A comparison with the results of other authors is given.

This study calculates and analyzes torsion moments of a rectangular panel with clamped edges as an element of ship structures under the action of uniform pressure with allowance for transverse shear deformation and examines the contribution of the corresponding shear stresses to the general stress state. In order to solve this problem, the method of infinite superposition of corrective functions of bending and stresses is applied. It involves an iterative process of mutually correcting the discrepancies from the said functions while meeting all boundary conditions. A particular solution for the bending function in the form of a quadratic polynomial is chosen as the initial approximation. It is established that torsion moment series diverge at the corner points of the plate going into infinity, which yields infinite values for the shear stresses at these points as well. Results of torsion moment calculation for square plates with different width ratios are provided. A 3D distribution diagram of moments is obtained. The computational experiment confirms the correctness of theoretical conclusions about infinite torsion moments at the corner points of the plate. Comparison with bending moments shows that torsion moments cannot be ignored during the assessment of the stress-strain state. The behavior of torsion moments near the corner points is qualitatively different from the simplified Kirchhoff theory, where they turn into zero.

Noble metal-based catalysts are widely used to intensify the processes of reductive fractionation of lignocellulose biomass. In the present investigation, we proposed for the first time using the inexpensive NiCuMo/SiO2 catalyst to replace Ru-, Pt-, and Pd-containing catalysts in the process of reductive fractionation of abies wood into bioliquids and cellulose products. The optimal conditions of abies wood hydrogenation were selected to provide the effective depolymerization of wood lignin (250 °C, 3 h, initial H2 pressure 4 MPa). The composition and structure of the liquid and solid products of wood hydrogenation were established. The NiCuMo/SiO2 catalyst increases the yield of bioliquids (from 36 to 42 wt%) and the content of alkyl derivatives of methoxyphenols, predominantly 4-propylguaiacol and 4-propanolguaiacol. A decrease in the molecular mass and polydispersity (from 1870 and 3.01 to 1370 Da and 2.66, respectively) of the liquid products and a threefold increase (from 9.7 to 36.8 wt%) in the contents of monomer and dimer phenol compounds were observed in the presence of the catalyst. The solid product of catalytic hydrogenation of abies wood contains up to 73.2 wt% of cellulose. The composition and structure of the solid product were established using IRS, XRD, elemental and chemical analysis. The data obtained show that the catalyst NiCuMo/SiO2 can successfully replace noble metal catalysts in the process of abies wood reductive fractionation into bioliquids and cellulose. [ABSTRACT FROM AUTHOR]

Hydrothermal transformation of microcrystalline cellulose (isolated from birch wood) under the influence of Al2O3-B2O3 mixed oxide solid acid catalysts was studied at temperatures of 180 and 215 °C (catalyst and cellulose were mix-milled in an AGO-2 planetary mill). At 180 °C, during the first hour, the average accumulation rates of glucose and 5 hydroxymethylfurfural attain 1030 and 320 mg of product per gram catalyst per hour, respectively. This activity exceeds typical values for sulfonated carbons bearing a similar concentration of acid groups (2.5 times faster glucose accumulation, 4.4 times faster 5-hydroxymethylfurfural accumulation). However, rapid accumulation of unhydrolyzed cellooligosaccharides in the reaction solution causes inhibition of the hydrolysis process after the first hour, probably via oligosaccharide chemisorption on the catalytically active acid sites, which leads to their deactivation. After the process at 180 °C, the catalysts can be washed with water and used again without significant loss of the catalytic performance; after four consecutive runs with the same catalyst, the combined yield of glucose, 5-hydroxymethylfurfural and furfural decreases by 15% compared with the first run. While the catalysts show considerable activity toward acid conversion of glucose into 5-hydroxymethyl furfural, the commonly observed next stage of such conversion into levulinic acid notably does not occur at 180 °C and proceeds at 215 °C. [ABSTRACT FROM AUTHOR]

The operating parameters of present-day engines depend on many factors, including the lubrication system. The lubrication system not only reduces friction between the surfaces of moving parts, but also contributes to their cooling and cleans engine parts from carbon deposits and impurities. High environmental requirements are also imposed on the quality of the lubricants, while maintaining their specifications. To that end, various additives are added to lubricating oil. The paper studies the effect of fine powders (enamels) on the wear of friction pairs in laboratory tests. The tests are mainly carried out for all-season synthetic and mineral oils in demand. Such criteria as wear of a roller and upper and lower bearings, specific wear of friction pairs, moment load, and temperature are selected as the effectiveness evaluation criteria of the use of enamels and nanomaterials. Experimental studies show a high efficiency of using enamels as additives to reduce friction and increase the load-carrying capacity of oils. The temperature in the friction layer is reduced by 10-20%, depending on the enamel concentration in the oil. The enamel acts as a third body with a lower friction coefficient and energy to failure, which increases the actual contact area of the friction pairs. The results of the study can be applied in the development of motor oils with fine enamel as an additive. [ABSTRACT FROM AUTHOR]