Tver State University (Russian: Тверской государственный университет) is a university in the city of Tver and one of the largest universities in the Tver Oblast, of which Tver is the administrative center. It has been licensed to conduct activities in the field of vocational education since April 1, 1999. The university has a major research library with more than one million copies. There is active research work, conferences and seminars.
Here, we develop a novel magnetically recoverable biocatalyst based on hyper-cross-linked polystyrene (HPS) with incorporated magnetite nanoparticles (NPs) and adsorbed cellulase (Cel) for the hydrolysis of carboxymethylcellulose (CMC, a water-soluble analogue of cellulose) to glucose. The biocatalyst demonstrates excellent performance both in a single reaction (preserved 95% of activity of native Cel) and in repeated use (preserved 93% of its initial activity after five consecutive reactions). To understand the origin of such behavior, the biocatalyst has been extensively studied using a combination of multiple physicochemical methods. HPS-Fe3O4-Cel porosity has been found to be lower compared to that of HPS upon incorporation of iron oxide NPs and Cel adsorption; nevertheless, this decrease does not block the majority of larger mesopores, thus allowing for efficient mass transfer. The HPS-Fe3O4 support allows for high Cel loading, attributed to a combination of hydrophobic interactions of Cel with HPS (similar to HPS-Cel) and, most importantly, specific interactions of Cel with Fe3O4 NPs, creating optimal conditions for the preservation of the Cel conformation. We believe the commercially available HPS along with facile preparation of magnetic NPs and Cel adsorption paves the way for the fabrication of a family of enzymatic catalysts for sustainable processes.
Understanding the thermal stability of hollow metal nanoframes remains a significant challenge due to strongly coupled effects such as porosity, curvature, and defect migration. Using tight-binding Monte Carlo simulations, we systematically investigate gold and silver nanoframes with cavity radii of 7.0-19.9 Å and quantitatively resolve their structural evolution through a shape-parametrization method that tracks cavity collapse and global flattening with ångström-level precision. Silver nanoframes exhibit lateral pore closure at 605-785 K, cavity collapse at 783-844 K, and melting near 852-900 K. Gold analogues show earlier pore closure (585-720 K) but higher collapse temperatures (688-823 K) and melting at 772-825 K, consistent with more coordinated recrystallization. The flattening parameter rises to 0.18-0.22 before global deformation, serving as a universal geometric indicator. Together, these quantitative criteria advance mechanistic understanding and enable the predictive design of thermally robust porous metal nanostructures.
Hydrogels based on a supramolecular low-concentrated gel-precursor―a cysteine–silver solution (CSS)―and the polysaccharide sodium alginate (SA), which is a polyanion, were obtained in this work. Gelation initiated in the cysteine–silver solution by the polysaccharide or by the MgSO4 electrolyte anion was studied in various systems (CSS–SA, CSS–SA–MgSO4, CSS–MgSO4) using vibroviscometry, UV spectroscopy, dynamic and electrophoretic light scattering, and scanning electron microscopy. It was found that the introduction of SA into the cysteine–silver solution at concentrations ranging from 0.01 to 0.05 mg/mL does not lead to hydrogel formation; gels are formed only in the presence of a sulfate-containing electrolyte at a concentration of 0.3 to 0.6 mM, but they are not strong and are easily disrupted by mechanical action. UV spectroscopy showed that in the gel-precursor spectrum, under the influence of SA macromolecules, the intensity of the absorption bands at 312 and 390 nm decreases due to a change in the geometry of the cluster chains of silver mercaptide [—Ag–S(R)—Ag–S(R)—]ₙ. According to dynamic and electrophoretic light scattering data, positively charged aggregates are formed in the CSS–SA system due to electrostatic interactions between the chain structures of CSS and SA molecules.
Small cities are a popular subject of geographical research. Modern studies most often examine the sociodemographic and economic issues of the functioning of such settlements. This article examines the spatial changes that have occurred in small cities in Russia in the post-Soviet period. Using satellite imagery of 190 small cities in noncapital regions of Central Russia, an analysis of changes in the area of built-up territories from 1989 to 2023 was conducted. During the period under review, 85 of the 190 small cities increased their area by more than 10
An approximate analytical solution of the Lame problem for a hollow sphere is obtained for isotropic compressible elastoplastic materials under large elastic and plastic deformations. This solution generalizes the known solution by R. Hill [1] to the case when not only plastic but also elastic deformations are large. To describe elastic deformations, nonlinear constitutive relations previously proposed by the authors are used, which reduce to the Murnaghan equation of state in the case of purely volumetric deformation. To describe plastic deformations, two models of ideal plasticity theory are used: a model based on the Mises yield criterion and the associated flow rule, and a model based on the Drucker–Prager yield criterion and a non-associated flow rule. For these classes of materials, approximate analytical solutions of the Lame problem under large elastic and plastic deformations are obtained. Nonlinear effects and effects due to plasticity are investigated. One of these effects is that there is a limiting pressure that can be applied to the inner boundary of the hollow sphere. Another effect is that the solution for given pressure can be not unique. The detailed analysis is performed for the case in which the hollow sphere is expanded under the action of pressure applied to its internal boundary.
