A TR ESR Study of the Quenching of Photoexcited Dioxouranium (VI) Salts by Stable Nitroxyl Free Radicals

TR ESR spectroscopy was applied to the study of the quenching of excited dioxouranium (VI) (uranyl) nitrate and sulfate by stable nitroxyl radicals of the 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) family. Photoexcitation of uranyl in solutions of alcohols of moderate viscosity (η = 3-10 cP) in the presence of TEMPO leads to CIDEP signals of TEMPO due to a radical triplet pair mechanism (RTPM). Polarized nitroxyls were also observed in solutions of polyelectrolyte sodium poly(styrenesulfonate), NaPSS, in the presence of the nitroxyl with a positively charged trimethylammonium group. Photolysis of uranyl salts in solutions of alcohols leads to the generation of free radicals of alcohols. No CIDEP of these radicals was observed, distinguishing U2 2+* from its organic analog, the triplet benzophenone. The probable reason for the lack of polarization in uranyl photoreduction reactions is the difficult access of free radicals to the U atom of the solvated radical UO2+ (V); this atom bears the unpaired electron. The role of polyelectrolytes in the enhancement of the quenching of excited states is discussed. Results are in agreement with the statement that photoexcited uranyl has a triplet multiplicity

Vector Particle Interactions In the Quasipotential Approach

The composite system, formed by two $S=1$ particles, is considered. The field operators of constituents are transformed on the $(1,0)\oplus (0,1)$ representation of the Lorentz group. The problem of interaction of $S=1$ particle with the electromagnetic field is also discussed.Comment: LateX file, 7pp., Preprint IFUNAM FT-93-01

Free Energy of an SU(2) Model of (2+1)-dimensional QCD in the Constant Condensate Background

Gluon and quark contributions to the thermodynamic potential (free energy) of a (2+1)-dimensional QCD model at finite temperature in the background of a constant homogeneous chromomagnetic field H combined with A_0 condensate are calculated. The role of the tachyonic mode in the gluon energy spectrum is discussed. A possibility of the free energy global minimum generation at nonzero values of H and A_0 condensates is investigated.Comment: LaTeX 2e, 14 pages, 6 eps figures, some miscalculations were correcte

Measurement of the K+→μ+νμγK^+\rightarrow{\mu^+}{\nu_{\mu}}{\gamma} decay form factors in the OKA experiment

A precise measurement of the vector and axial-vector form factors difference $F_V-F_A$ in the $K^+\rightarrow{\mu^+}{\nu_{\mu}}{\gamma}$ decay is presented. About 95K events of $K^+\rightarrow{\mu^+}{\nu_{\mu}}{\gamma}$ are selected in the OKA experiment. The result is $F_V-F_A=0.134\pm0.021(stat)\pm0.027(syst)$. Both errors are smaller than in the previous $F_V-F_A$ measurements.Comment: 9 pages, 8 figure

The Design Optimization and Experimental Investigation of the 4.4 μm Raman Laser Basedon Hydrogen-filled Revolver Silica Fiber

Optical properties of hollow-core revolver fibers are numerically investigated depending on various parameters: the hollow-core diameter, the capillary wall thickness, the values of the minimum gap between the capillaries, the number of capillaries in the cladding and the type of glass (silica and chalcogenide). Preliminary, similar calculations are made for simple models of hollow-core fibers. Based on the obtained results, the optimal design of the revolver fiber for Raman laser frequency conversion (1.56 μm → 4.4 μm in 1H2) was determined. As a result, efficient ns-pulsed 4.42 μm Raman laser based on 1H2-filled revolver silica fiber is realized. Quantum efficiency as high as 36 % is achieved and output average power as high as 250 mW is demonstrated

Magnetic catalysis of parity breaking in a massive Gross-Neveu model and high-temperature superconductivity

In the framework of a (2+1)-dimensional P-even massive Gross-Neveu model, an external magnetic field is shown to induce a parity breaking first order phase transition. Possibility of applying the results obtained to description of magnetic phase transitions in high-temperature superconductors is discussed.Comment: LaTeX 2.09, 8 pages, 2 eps figure

Raman and XANES Spectroscopic Study of the Influence of Coordination Atomic and Molecular Environments in Biomimetic Composite Materials Integrated with Dental Tissue

In this work, for the first time, the influence of the coordination environment as well as Ca and P atomic states on biomimetic composites integrated with dental tissue was investigated. Bioinspired dental composites were synthesised based on nanocrystalline calcium carbonate-substituted hydroxyap-atite (Formula presented) (nano-cHAp) obtained from a biogenic source and a set of po-lar amino acids that modelled the organic matrix. Biomimetic composites, as well as natural dental tissue samples, were investigated using Raman spectromicroscopy and synchrotron X-ray absorption near edge structure (XANES) spectroscopy. Molecular structure and energy structure studies revealed several important features related to the different calcium atomic environments. It was shown that biomimetic composites created in order to reproduce the physicochemical properties of dental tissue provide good imitation of molecular and electron energetic properties, including the carbonate anion CO32− and the atomic Ca/P ratio in nanocrystals. The features of the molecular structure of biomimetic composites are inherited from the nano-cHAp (to a greater extent) and the amino acid cocktail used for their creation, and are caused by the ratio between the mineral and organic components, which is similar to the composition of natural enamel and dentine. In this case, violation of the nano-cHAp stoichiometry, which is the mineral basis of the natural and bioinspired composites, as well as the inclusion of different molecular groups in the nano-cHAp lattice, do not affect the coordination environment of phosphorus atoms. The differences observed in the molecular and electron energetic structures of the natural enamel and dentine and the imitation of their properties by biomimetic materials are caused by rearrangement in the local environment of the calcium atoms in the HAp crystal lattice. The surface of the nano-cHAp crystals in the natural enamel and dentine involved in the formation of bonds with the organic matrix is character-ised by the coordination environment of the calcium atom, corresponding to its location in the CaI posi-tion—that is, bound through common oxygen atoms with PO4 tetrahedrons. At the same time, on the surface of nano-cHAp crystals in bioinspired dental materials, the calcium atom is characteristically lo-cated in the CaII position, bound to the hydroxyl OH group. The features detected in the atomic and molecular coordination environment in nano-cHAp play a fundamental role in recreating a biomimetic dental composite of the natural organomineral interaction in mineralised tissue and will help to find an optimal way to integrate the dental biocomposite with natural tissue. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.This work was supported by a grant from the Russian Science Foundation, grant number 21-75-10005; The access to scientific equipment and methodology was provided under support of the Ministry of Science and Higher Education of Russia, Agreement N 075-15-2021-1351