Recent publications

Existing trends in the development of technology for gypsum-containing materials include expansion of their application possibilities in systems of façade coatings, the usage of by-products of other industries and local gypsum-containing raw materials. Considering the low durability of gypsum materials in wet operating conditions, system solutions are being developed based on the use of various methods of gypsum modification, including the usage of polymers. The purpose of the research described in the article was to develop a method for selecting the composition of modified clay-gypsum binder, optimizing its compositions and assessing the properties of the materials obtained under conditions of high humidity. The experiment to assess the influence of the composition of the modified clay-gypsum binder on its properties was carried out according to the general methodology of planning the experiment and analytical optimization of its results. The research results showed that the compressive strength of the clay gypsum samples with 15% modified melamine–formaldehyde resin in-creases by 15% after 80 days of storage in air. Products made of modified clay-gypsum have a fairly high frost resistance of 75 cycles and a softening coefficient of 0.95. The vapor permeability of the material is 0.088 mg/(m\(\cdot\)h\(\cdot\)Pa), which determines the favourable moisture regime of the load-bearing walls with lining with this material.
KeywordsGypsum binderClay gypsumAnalytical optimizationMoisture resistanceSoftening coefficient

In this article, four difference schemes for solving the boundary value problem for the non-stationary Aller-Lykov moisture transfer equation are proposed and investigated. The schemes are constructed in space and time using two methods, the finite differences method and the finite elements method. The stability and convergence of the constructed numerical algorithms are proved, and the estimates of the accuracy of the proposed difference schemes are obtained with sufficient smoothness of the solution to the original differential problem. A computational experiment was used to test the schemes. Their comparative analysis was performed.

We apply the method of inverse spectral problem to find the solution to the Cauchy problem for a modified Korteweg–de-Vries equation (mKdV) in the class of periodic infinite-gap functions. A simple procedure is proposed for the derivation of the Dubrovin system of differential equations. We prove the solvability of the Cauchy problem for an infinite system of Dubrovin differential equations in the class of five times continuously differentiable periodic infinite-gap functions. It is shown that the sum of a uniformly convergent function series constructed from the solutions of the infinite system of Dubrovin equations and the formulas for the first trace satisfy the mKdV equation. Moreover, it is proved that: (i) if the initial function is a real π-periodic analytic function, then the solution of the Cauchy problem for the mKdV equation with loaded term is also a real analytic function with respect to the variable x; (ii) if the number π2 is a period (antiperiod) of the original function, then π2 is also a period (antiperiod) in the variable x of the solution to the Cauchy problem for the mKdV equation with loaded term.

The Aral Sea has been persistently shrinking in past decades, and the influence of the lake water level changes on vegetation in the lake retreat areas is uncertain. In this study, we quantitatively assessed the vegetation development due to relevant hydrological changes in the retreat area of the Aral Sea. The results showed that the normalized difference vegetation index (NDVI) in the retreat area displayed an overall increase from 1986 to 2020. The increasing vegetated area accounted for 84% of the total area of the South Aral Sea, which was caused by an increase in the exposed lakebed area. However, about 40 % of the area in the North Aral Sea was the increasing vegetated area due to the improved water environment. When the depth to water table (DTW) was larger than 7–8 m, vegetation development was more dependent on precipitation than groundwater. When DTW was less than 7–8 m, groundwater had a more significant impact than precipitation on vegetation development. The negative impacts of groundwater salinity exceed the positive contributions of water supply on vegetation development, which differs to the common understanding under conditions of fresh or brackish groundwater in arid climates. Water level recovery is an effective option for improving vegetation establishment on the exposed seabed; otherwise, the exposed seabed area observed during the period 1990s–2010s in the eastern basin may remain a saline desert for a long period in the future. Finally, an empirical relationship between NDVI and water levels was established, which can be used for lake water level management that considers vegetation development in the retreated area of the Aral Sea.

The aim of this work is study of physical and chemical properties of dust of the Pre-Aral region of Uzbekistan such as Karakalpakstan and Khorezm that are located near the three deserts such as the Aralkum, Karakum, and Kyzylkum. The dust particles fell on glass have been collected in Karakalpakstan and Khorezm and studied systematically by employing wide range of methods. Particle volume vs size distribution has been measured with maximum around 600 nm and ~ 10 µm. The major and minor constituent materials present in the dust have been studied systematically by X-ray fluorescence spectroscopy, energy dispersive X-ray diffraction, and inductively coupled plasma optical emission spectroscopy. Main characteristic absorption bands corresponding to Si–O, Si–O-Si bonding in quartz and Fe–O bonds in hematite Fe2O3 have been identified by infrared and Raman spectroscopy. Quartz, hematite, lime, corundum, magnesia, and several other trace minerals have been identified in the dust particles. X-ray diffraction peaks corresponding to quartz, hematite, and corundum are sharp and are found to be more crystalline with some level of disorder. Analysis of the particle size and crystallinity on human being has been performed: disordered or crystalline quartz can create the lung disease; the particles in the size of 0.5–0.7 µm may produce diseases such as chronic silicosis, silicosis, and silica tuberculosis whereas hematite might create lung disease. Dust particles worsen optical transmittance of glass of the panels.
Graphical abstract

A photovoltaic module has been designed from five buspar crystalline silicon solar cells fabricated by Suzhou Talesun Solar Technologies Co., Ltd. Short-circuit current and open-circuit voltage of the modules has been studied as a function of the illumination intensity and temperature in laboratory conditions. Upon increasing the temperature from T = 22 °C to 50 °C open-circuit voltage decreases from ∼9 to ∼7 V whereas short-circuit current slightly increases from 1.88 to 2.00 A. The results have been compared with theoretical results obtained by device modeling by using the software SCAPS-1D. Infrared image has been taken from the module by using the EEFSC computer-controlled photovoltaic solar energy unit. Mass of dust fallen on photovoltaic module has been collected and measured within two-month time. Influence of the dust on transmittance spectra of glass has been studied.

This paper is devoted to study of local and 2-local derivations on octonion algebras. We shall give a general form of local derivations on the real octonion algebra [Formula: see text] This description implies that the space of all local derivations on [Formula: see text] when equipped with Lie bracket is isomorphic to the Lie algebra [Formula: see text] of all real skew-symmetric [Formula: see text]-matrices. We also consider [Formula: see text]-local derivations on an octonion algebra [Formula: see text] over an algebraically closed field [Formula: see text] of characteristic zero and prove that every [Formula: see text]-local derivation on [Formula: see text] is a derivation. Further, we apply these results to similar problems for the simple seven-dimensional Malcev algebra. As a corollary, we obtain that the real octonion algebra [Formula: see text] and Malcev algebra [Formula: see text] are simple non-associative algebras which admit pure local derivations, that is, local derivations which are not derivation.

The article modern solutions to improve land reclamation, suggestions and recommendations for the sustainable development of processes for the protection of natural resources. The analysis shows that over the years of reforms in Uzbekistan, there has been a tendency to increase the fertility of irrigated lands in all districts, except for Karauzak, Kungrad, Takhtakor, Shumanoi and Khodjayli. In particular, the assessment of irrigated crops increased significantly in Nukus (8 points), Moinak (5 points), Amu Darya (3 points), Kegeyli (2 points), Chimbay (2 points). The productivity of irrigated lands during this period increased from 41 to 42 points.

The present paper is devoted to study of band preserving isomorphisms of commutative unital regular algebras. Let A be a commutative unital regular algebra over an algebraically closed field F of characteristic zero and let ∇=∇(A) be the Boolean algebra of all idempotents in A. Assume that μ is a finite strictly positive countable-additive measure on ∇ and let A be complete with respect to the metric ρ(x,y)=μ(s(x-y)),x,y∈A. We prove that if B is a subalgebra of A such that B⊃∇, then for any band preserving monomorphism Φ:B→B there exists a band preserving monomorphism Ψ:A→A such that Ψ|B=Φ. Further we introduce a notion of transcendence degree of a commutative unital regular algebra and prove that two homogeneous unital regular subalgebras of S(Ω) – the algebra of all classes of measurable complex-valued functions on a Maharam homogeneous measure space (Ω,Σ,μ), are isomorphic if and only if their Boolean algebras of idempotents are isomorphic and their transcendence degrees coincide. As an application we obtain that the regular algebra S(0; 1) – of all classes of measurable complex-valued functions and the algebra AD(0; 1) – of all classes of approximately differentiable functions on [0; 1] are isomorphic.

The article examines the right of citizens to participate in the management of state affairs, its constitutional features. Special attention is paid to its role and place in the system of constitutional human and civil rights and freedoms. It is concluded that the participation of citizens in the management of state affairs is one of the guarantors of ensuring the rights and freedoms of the individual and the most important institution of a democratic society.

Clay gypsum as a natural material of sedimentary origin is widespread both in Russia and in the states formed in the post-Soviet space. In terms of energy intensity and manufacturability, the processing of raw materials into a clay-gypsum binder does not differ from the conditions of traditional processing of natural gypsum. Compared to lime or cement mortars, mortars based on gypsum binder have greater elasticity and plasticity. Such properties associated with the manufacturability of the application, such as workability and thixotropy, as well as the interval for maintaining the pot life of the mixture, are controlled by the introduction of modifying additives, the evaluation of the formulation of which was the purpose of the research, the results of which are presented in the article. The studies carried out have established that varying the recipe parameters make it possible to regulate both the strength and performance characteristics of mixtures based on gypsum plaster, as well as the manufacturability of their application.

It is established that every Banach–Kantorovich algebra over a ring of measurable functions can be represented as a measurable bundle of Banach algebras with a vector-valued lifting. Using this representation we prove non emptiness and cyclic compactness of the spectrum of an element in a Banach–Kantorovich algebra over a ring of measurable functions. Further we give some applications of the main result to bounded homomorphisms on Kaplansky–Hilbert modules and partial integral operators on function spaces with a mixed norm.

It has been shown experimentally that nickel clusters on the surface of a silicon sample contain a large amount of oxygen and recombination impurities --- Cu, Fe, Cr, and so shows good gettering properties of clusters. The optimum temperature of nickel diffusion into silicon is determined as 800-850 o C. Doping with impurity nickel atoms with the formation of clusters makes it possible to increase the lifetime of nonequilibrium charge carriers in the base of a solar cell by up to 2 times, while the formation of a nickel-enriched region in the face layer is more efficient. It is shown that the effect of additional doping with nickel weakly depends on the sequence of the processes of nickel diffusion and the creation of a working p-n-junction. Keywords: silicon solar cells, nickel diffusion, nonequilibrium charge carriers, gettering, p-n junction.

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