Due to rare earth doping, phosphates and vanadates are the leading materials for the synthesis of phosphors due to their thermal stability, low sintering temperature, and chemical stability. Phosphors in the nanoscale state are of particular interest. The simple, fast, and scalable synthesis of nanophosphors with high chemical homogeneity is a priority task. The purpose of this work was to synthesize powders of mixed yttrium vanadate-phosphate crystals of various compositions by coprecipitation under the action of microwave radiation and spray pyrolysis, as well as to compare the characteristics ofthe obtained samples. Samples of YVхP1–хO4 of different compositions were synthesized by coprecipitation under the action of microwave radiation and spray pyrolysis in different modes. In the case of the synthesis of yttrium vanadate-phosphate YVхP1–хO4 by spray pyrolysis followed by annealing, according to the X-ray phase analysis data, single-phase nanopowders were formed. The morphological characteristics of the samples were revealed by the methods of transmission electron microscopy and scanning electron microscopy. Depending on the annealing conditions, the samples were either faceted or spherical particlesless than 100 nm in size. The composition of the YVхP1–хO4 , samples synthesized by the coprecipitation method under the action of microwave radiation strongly depended on the pH of the precursor solution. The minimum content of impurity phases was reached at pH 9.Spray pyrolysis allows the synthesis of yttrium vanadate phosphate YVхP1–хO4 nanopowders of high chemical homogeneity with a particle size of less than 100 nm. The maximum chemical homogeneity of yttrium vanadate-phosphate powders was achieved at pH = 9 during the synthesis of YVхP1–хO4 by coprecipitation under the action of microwave radiation. However, the particle size dispersion was large, within the range of 2–60 μm. References 1. Wu C., Wang Y., Jie W. 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A numerical analytical approach is proposed to study the natural vibrations of thin isotropic conical shells with varying thickness. The approach is based on the spline-approximation of unknown functions. Open shells (panels) with different boundary conditions are considered. The effect of variable thickness on the dynamic characteristics is analyzed Keywords: natural vibrations, thin isotropic conical shell, spline-collocation Introduction. Conical shells of variable thickness are widely used in many fields of modern engineering. An important aspect in making the shells strong is data on their natural vibrations. Recent trends in mathematics, mathematical physics, and mechanics are toward the wide use of spline-functions owing to their advantages over other methods of approximation. The main advantages of splines are their stability against local perturbations and the good convergence of the methods that employ splines as approximating functions. Using spline-functions in various variational, projective, and other discrete continuous methods makes it possible to refine the results of the classical polynomial approximation, to simplify considerably their numerical implementation, and to obtain a highly accurate solution.The present paper analyzes the natural vibrations of conical isotropic shells (panels) of variable thickness with different boundary conditions. Since the separation of variables is impossible for this class of shells, it is necessary to employ numerical methods.This paper proposes an efficient numerical method for studying the natural frequencies and modes of conical shells with varying thickness. The method involves spline-approximation in one coordinate direction and solution of a boundary-value eigenvalue problem for systems of ordinary differential equations of high order with variable coefficients by stable numerical discrete orthogonalization in combination with step-by-step search [3,4]. Such an approach was used in [6][7][8][9].This method allows analyzing the natural vibrations of conical shells (panels) with arbitrarily varying thickness and complex boundary conditions. 1. Problem Statement. Consider a problem on natural vibrations of an isotropic conical shell with varying thickness h x y ( , )in the curvilinear orthogonal coordinate system ( , ) s q , where s is the length of a meridian arc; q is the central angle in a parallel circle. In this case, the Lode parameters are: A = 1, B = r. The radii of principal curvatures R s and R q are: R s = 0, R r
The protonation of a number of 4,6-dihydroxypyrimidine derivatives is studied, and the features of the electronic spectra of free bases and protonated forms are considered. It is shown that the alkyl substituents in position 2 increase the basicity of the compound, and the nitro group in position 5 leads to its decrease. In an acid medium (0.1−99.5% H 2 SO 4 ), 4,6dihydroxypyrimidine, 6-hydroxy-2-methylpyrimidine-4(3H)-one, and 6-hydroxy-2-ethylpyrimidine-4(3H)-one have two protonation stages, barbituric acid is protonated in three stages, and 6-hydroxy-2-methyl-5-nitropyrimidine-4(3H)-one and 6-hydroxy-2-ethyl-5-nitropyrimidine-4(3H)-one form a monocation.
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