A U(1) Current Algebra Model Coupled to 2D-Gravity

We consider a simple model of a scalar field with $U(1)$ current algebra gauge symmetry coupled to $2D$-gravity in order to clarify the origin of Stuckelberg symmetry in the $w_{\infty}$-gravity theory. An analogous symmetry takes place in our model too. The possible central extension of the complete symmetry algebra and the corresponding critical dimension have been found. The analysis of the Hamiltonian and the constraints shows that the generators of the current algebra, the reparametrization and the Stuckelberg symmetries are not independent. The connection of the model with $w_{1+\infty}-$ and $W_{1+\infty}$-gravity is discussed.Comment: INRNE-TH/02/93, LaTeX, 11 pages, (slight change of title and other minor changes

Central Extension of a New W∞W_\infty - Type Algebra

The central extension of a new infinite dimensional algebra which has both $W_\infty$ and affine $sl(2,R)$ as subalgebras is found. The critical dimension of the corresponding string model is $D=5$.Comment: 6p., LaTeX, IC/94/20

Molecular dynamics study of the stability of aluminium coatings on iron

Among the available protection systems for steel, the use of coatings is the most popular and economical method. One can protect the steel electrode from aggressive media with an aluminum coating. A thin Al film on an Fe substrate has been studied by the molecular dynamics method at a heating temperature from 300 K to 1500 K. A significant horizontal displacement of individual Al atoms on the edges of the film is observed during the simulation. The film begins to “spread” slightly near the edges. This “spreading” creates the conditions for the beginning of diffusion of iron atoms into aluminum. Some Al atoms were found to penetrate the Fe matrix at a temperature of 873 K. The total energy curve of the system shows both the melting transition in aluminum and phase transition from the body-centered cubic lattice to the face-centered cubic one at 1173 K. The binding energy for the Al atom in the lattice of the Fe crystal is smaller than that for Fe atoms. The calculated diffusion coefficients for Al and Fe have a significantly slower growth with a temperature in the range of 673 K ≤ T ≤1500 K. To describe the diffusion in a crystal using the molecular dynamics model, a temperature-dependent correction to the activation energy is calculated. The temperature dependence of the diffusion coefficient of aluminum atoms in an iron crystal can be represented as an Arrhenius expression with a temperature-dependent energy barrier for diffusion. © 2019, Institute for Metals Superplasticity Problems of Russian Academy of Sciences. All rights reserved

Physical aspects of the lithium ion interaction with the imperfect silicene located on a silver substrate

Epitaxy of Si on a silver substrate is the main method to obtain silicene. The latter does not separate from the substrate. In the present paper, the possibility of using silicene on a silver substrate as an anode for lithium-ion batteries is studied by the method of molecular dynamics. Structural and mechanical effects arising from the motion of a Li + ion through a planar channel formed by a perfect and defective two-layer silicene are studied. Generally, the defect stability and silicene sheet integrity are independent of the Ag(001) or Ag(111) substrate type. The transverse vibrations of Si atoms in the channel have a significant effect on the motion of lithium ions. This effect is taken into account by using the interference factor that describes the slowing down of the motion of the Li + ion in the channel. The dependence of this coefficient on the size of vacancy defects in silicene is determined. The presence of the substrate makes this dependence less relevant. The stress distribution in the defective silicene while driving a lithium ion along the planar silicene channel is calculated. The strongest stresses in the silicene are created by forces directed perpendicular to the strength of the external electric field. These forces dominate in the silicene channel placed on the substrates of both types. © 2018, Institute for Metals Superplasticity Problems of Russian Academy of Sciences. All rights reserved.Acknowledgements. This study is supported by the Russian Science Foundation (project no. 16‑13‑00061)

Modeling the UO2 reduction process

Methods of molecular dynamics and DFT calculations have been used to study the reduction mechanisms of UO2 as the most representative part of spent nuclear fuel to metallic uranium. It is shown that the critical softening of the combined modulus of elasticity C11-C12 to zero is the reason for the destruction of the UO2 crystal as a result of the removal of oxygen from it. This destruction is accompanied by an order-disorder phase transition in the oxygen subsystem of the crystal under consideration. DFT calculations indicate a continuous decrease in the band gap as oxygen is removed from the UO2 crystal. When the system reaches the composition U2O3, the band gap disappears and the system becomes electrically conductive. The appearance of the dielectric-conductor transition explains the realization of the FFC Cambridge process during the recovery of spent nuclear fuel. The passage of Li+ and Cl– ions of the LiCl melt through cylindrical channels in a UO2 crystal with cross-sectional radii from 0.25 up to 2 nm has been studied. The strength of the external electric field required for the passage of these channels decreases with an increase in the channel cross section, and the number of Cl– ions entering the channel increases. On the walls of the channels that pass ions with charges of both signs, colonies of adsorbed Cl– and Li+ atoms appear separated from each other, between which strong electric fields are formed. The existence of such fields can cause Li+ ions to move deep into the material being reduced.https://doi.org/10.15826/elmattech.2023.2.01

Electrode processes during the electrorefiniment of lead in the KCl-PbCl2-PbO melt

The influence of PbO addition on current efficiency during the electrorefinement of lead in the KCl-PbCl2-PbO melt was investigated. It was shown that with PbO concentration in the KCl-PbCl2 eqiumolar mixture increasing, the current efficiency of lead decreases. Electrode processes mechanism is proposed

Kinetic test of a doped silicene-graphite anode element in a computer experiment

The stability of the system "bi-layer silicene on the graphite substrate" is studied in the molecular dynamics simulation. Silicene sheets are doped with phosphorus, and graphite sheets are doped with nitrogen. Lithium ion moves along a silicene channel with a gap in the range of 0.6-0.8 nm. The time for the ion to pass the channel and leave it decreases with an increase in the channel gap. There is a tendency of the silicene sheets roughness growth with an increase in the gap between silicene sheets (except, 0.75 nm). Doping phosphorus and nitrogen atoms stabilize the silicene and graphite structure. © 2020 Published under licence by IOP Publishing Ltd.Russian Science Foundation, RSF: 16-13-00061The study is supported by the Russian Science Foundation (project no. 16-13-00061)

Ab Initio Study of the Mechanism of Proton Migration in Perovskite LaScO3

The mechanism of proton motion in a LaScO3 perovskite crystal was studied by ab initio molecular dynamics. The calculations were performed at different temperatures, locations, and initial velocity of the proton. Different magnitudes and directions of the external electric field were also considered. It is shown that initial location and interaction between proton and its nearest environment are of great importance to the character of the proton movement, while the magnitude and direction of the initial velocity and electric field strength are secondary factors characterizing its movement through the LaScO3 crystal. Four types of proton-jumping between oxygen atoms are determined and the probability of each of them is established. Energy barriers and characteristic times of these jumps are determined. The probable distances from a proton to other types of atoms present in perovskite are calculated. It is shown that the temperature determines, to a greater extent, the nature of the motion of a proton in a perovskite crystal than the magnitude of the external electric field. The distortion of the crystal lattice and its polarization provoke the formation of a potential well, which determines the path for the proton to move and its mobility in the perovskite crystal. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.122020100205-5, FUME-2022-0005; Government Council on Grants, Russian Federation: 075-03-2022-011, FEUZ-2020-0037Funding: This work is partly supported by Government of Russian Federation, the State Assignment number FEUZ-2020-0037, registration number 075-03-2022-011; and is partly executed in the frame of the scientific theme of Institute of high-temperature electrochemistry UB RAS, number FUME-2022-0005, registration number 122020100205-5

Anode Processes on Pt and Ceramic Anodes in Chloride and Oxide-Chloride Melts

Platinum anodes are widely used for metal oxides reduction in LiCl–Li2O, however high-cost and low-corrosion resistance hinder their implementation. NiO–Li2O ceramics is an alternative corrosion resistant anode material. Anode processes on platinum and NiO–Li2O ceramics were studied in (80 mol.%)LiCl-(20mol.%)KCl and (80 mol.%)LiCl-(20 mol.%)KCl–Li2O melts by cyclic voltammetry, potentiostatic and galvanostatic electrolysis. Experiments performed in the LiCl–KCl melt without Li2O illustrate that a Pt anode dissolution causes the Pt2+ ions formation at 3.14 V and 550°С and at 3.04 V and 650оС. A two-stage Pt oxidation was observed in the melts with the Li2O at 2.40 ÷ 2.43 V, which resulted in the Li2PtO3 formation. Oxygen current efficiency of the Pt anode at 2.8 V and 650°С reached about 96%. The anode process on the NiO–Li2O electrode in the LiCl–KCl melt without Li2O proceeds at the potentials more positive than 3.1 V and results in the electrochemical decomposition of ceramic electrode to NiO and O2. Oxygen current efficiency on NiO–Li2O is close to 100%. The NiO–Li2O ceramic anode demonstrated good electrochemical characteristics during the galvanostatic electrolysis at 0.25 A/cm2 for 35 h and may be successfully used for pyrochemical treating of spent nuclear fuel. © 2021 Korean Nuclear Society.The present research was partially performed within the Proryv (Breakthrough) project of State Atomic Energy Corporation Rosatom

ВЗАИМОДЕЙСТВИЕ СПЕЧЕННОГО НИТРИДА АЛЮМИНИЯ С РАСПЛАВОМ KF–AlF3 ПРИ ТЕМПЕРАТУРАХ 700–800 °С

By means of continuous weighing method was investigated the kinetics of the interaction of sintered composite on the base of aluminium nitride with the molten potassium cryolite with cryolite ration (CR) 1,3 at temperatures of 700–800 °C. There was specified that at temperature 700 °C composite practically did not exposed to melt impact. Materials interact with molten salt through the stage of its oxidation in the melt of oxygen. At this, takes place besides merging of originally presented in material of oxygen-containing impurities. In the absence of an oxidizer and at concentration of dissolved in cryolite alumina, close to saturation, interaction of sintered aluminium nitride with examined melt did not observed.Методом непрерывного взвешивания исследована кинетика взаимодействия спеченного композиционного материала на основе нитрида алюминия с расплавом калиевого криолита с криолитовым отношением КО = 1,3 при температурах 700–800 °С. Установлено, что при t = 700 °C композит практически не подвергается воздействию расплава. Скорость коррозии возрастает при увеличении температуры. Материал взаимодействует с расплавленной солью через стадию его окисления растворенным в расплаве кислородом. При этом также происходит растворение изначально присутствующих в материале кислородсодержащих примесей. В отсутствие окислителя и при концентрации растворенного в криолите глинозема, близкой к насыщению, взаимодействия спеченного нитрида алюминия с исследуемым расплавом не наблюдалось