Получение пористых полимерных композитов

В данной работе мы экспериментально убедились в целесообразности использования метода прессования форм из композита с примесью NaCl с последующим удалением соли для получения пористой структуры композитов

Accumulation of heavy metals in birch and pine forest roadside phytocenoses in the south of Tyumen region

We conducted a complex investigation of anthropogenic roadside phytocoenoses. For the study, 8 plots (birch and pine forests) were selected, close to roads in the south of Tyumen region within the five administrative districts: Uporovsky, Zavodoukovsky, Yalutorovskiy, Yarkovsky, and Tobolsk. As a result of the studies, 75 species of vascular plants from 21 families were noted in the plant communities. It was found that the majority of the total projective cover of the plant communities was provided by synanthropic species. In the synanthropic fraction of the flora, 33 species belonging to 11 families were identified, those with the most species being: Scrophulariaceae, Compositeae, Rubiaceae, Poaceae, Fabaceae, Polygonaceae, Umbellíferae. The index of synanthropization of the flora of the studied phytocenoses is in the range from 43% to 64%. Among the identified pollutants accumulated in the phytocenoses, the group of heavy metals was identified (Cr, Cu, Ni, Pb, Sr, Zn). Needles of Pinus sylvestris L. mainly accumulate Cr, Cu, Ni, Sr. The greatest concentration of Pb and Zn was found in the leaves of Betula pendula Roth. The content of other heavy metals in the leaves of Betula pendula Roth. during the growing season was relatively stable. Accumulation of heavy metals in the studied components of forest ecosystems can be displayed structurally: soil > leaves < phytomass (birch forests), soil < needles > phytomass (pine forests). Methodological approaches to conducting a complex of long-term observations of natural ecosystems have been formulated, substantiated and justified. To evaluate the absorption efficiency of heavy metals, the biological absorption coefficient was calculated. The obtained results can be used as a control in the study of migration and accumulation of heavy metals and for assessing the degree of anthropogenic load on phytocenoses of roadside ecosystems and predict the extent of probable changes in them. The forecast of the results will facilitate the elaboration of a necessary system of measures aimed at increasing the stability of plant communities

Mathematical modeling of three-layer beam hydroelastic oscillations

The problem of hydroelastic oscillations of three-layer beam interacting with viscous liquid layer is set up and analytically solved. The problem presents the equation system of a three-layer beam and Navier-Stokes equations. The following boundary conditions are chosen: the no-slip conditions, the conditions for pressure at the edges, the simply supported edges conditions. The problem is solved for the steady-state harmonic regime. The frequency dependent distribution functions of the beam deflection are constructed. The given function allows investigating the resonance hydroelastic oscillations of a three-layer beam, as well as its deflected mode

Optical spectra, crystal-field parameters, and magnetic susceptibility of the new multiferroic NdFe3(BO3)4

We report high-resolution optical absorption spectra for NdFe3(BO3)4 trigonal single crystal which is known to exhibit a giant magnetoelectric effect below the temperature of magnetic ordering TN = 33 K. The analysis of the temperature-dependent polarized spectra reveals the energies and, in some cases, symmetries and exchange splittings of Nd3+ 84 Kramers doublets. We perform crystal-field calculations starting from the exchange-charge model, obtain a set of six real crystal-field parameters, and calculate wave functions and magnetic g-factors. In particular, the values g(perpendicular) = 2.385, g(parallel) = 1.376 were found for the Nd3+ ground-state doublet. We obtain Bloc=7.88 T and |JFN|= 0.48 K for the values of the local effective magnetic field at liquid helium temperatures at the Nd3+ site and the Nd - Fe exchange integral, respectively, using the experimentally measured Nd3+ ground-state splitting of 8.8 cm-1. To check reliability of our set of crystal field parameters we model the magnetic susceptibility data from literature. A dimer containing two nearest-neighbor iron ions in the spiral chain is considered to partly account for quasi-one-dimensional properties of iron borates, and then the mean-field approximation is used. The results of calculations with the exchange parameters for Fe3+ ions Jnn = -6.25 K (intra-chain interactions) and Jnnn = -1.92 K (inter-chain interactions) obtained from fitting agree well with the experimental data.Comment: 13 pages, 8 figures, 2 table

Sustainable import substitution in Russia : institutional conditions and efficiency imperatives

The article is devoted to the essence and relevance of import substitution as an effective strategy of Russian economy’s development within the sanctions’ constraint of Western countries. Authors scoped out the institutional features of sustainable import substitution as an object of the study. Authors highlighted the set of objective factors verifying the economic viability of import substitution and potential threats of these measures as well. Authors arranged the evaluation and analytical tools for studying the dependence on imports’ level in the context of certain industries, goods, and spheres of activity. Moreover, authors clarified the pattern for estimating the need for import substitution in a certain business entity, suggested the institutional conditions and determinants facilitating the best performance of import substitution in Russia. Special attention is given to the viability of choosing the appropriate model, developing tools, and mechanisms for implementing a comprehensive program of import substitution in Russia in the context of a multi-level policy including the following ones: enterprise - industry (cluster) – country’s economy. As a result, authors concluded that the policy of preemptive emerging markets-oriented import substitution aimed at improving the global economic security of Russian economy is crucial for a sustainable balanced development.peer-reviewe

Polystyrene-based nanocomposites with different fillers: fabrication and mechanical properties

The paper presents a comprehensive analysis of elastic properties of polystyrene-based nanocomposites filled with different types of inclusions: small spherical particles (SiO2 and Al2O3), alumosilicates (montmorillonite, halloysite natural tubules and Mica) and carbon nanofillers (carbon black and multi-walled carbon nanotubes). Composites were fabricated by melt technology. The analysis of composite melts showed that the introduction of Montmorillonite, Multi-walled carbon nanotubes, and Al2O3 particles provided an increase in melt viscosity by an average of 2 to 5 orders of magnitude over the pure polystyrene. Block samples of composites with different filler concentrations were prepared, and their linear and nonlinear elastic properties were studied. The introduction of more rigid particles led to a more profound increase in the elastic modulus of the composite, with the highest rise of about 80% obtained with carbon fillers. Carbon black particles provided also an enhanced strength at break of about 20% higher than that of pure polystyrene. The nonlinear elastic moduli of composites were shown to be more sensitive to addition of filler particles to the polymer matrix than the linear ones. The nonlinearity coefficient $\beta$ comprising the combination of linear and nonlinear elastic moduli of a material demonstrated considerable changes correlating with changes of the Young's modulus. The absolute value of $\beta$ showed rise in 1.5-1.6 times in the CB- and HNT-containing composites as compared to that of pure PS. The changes in nonlinear elasticity of fabricated composites were compared with measurements of the parameters of bulk nonlinear strain waves in them. Variations of wave velocity and decay decrement correlated with observed enhancement of materials nonlinearity