Stability analysis of dynamical regimes in nonlinear systems with discrete symmetries

We present a theorem that allows to simplify linear stability analysis of periodic and quasiperiodic nonlinear regimes in N-particle mechanical systems (both conservative and dissipative) with different kinds of discrete symmetry. This theorem suggests a decomposition of the linearized system arising in the standard stability analysis into a number of subsystems whose dimensions can be considerably less than that of the full system. As an example of such simplification, we discuss the stability of bushes of modes (invariant manifolds) for the Fermi-Pasta-Ulam chains and prove another theorem about the maximal dimension of the above mentioned subsystems

Magnetoelectric effect due to local noncentrosymmetry

Magnetoelectrics often possess ions located in noncentrosymmetric surroundings. Based on this fact we suggest a microscopic model of magnetoelectric interaction and show that the spin-orbit coupling leads to spin-dependent electric dipole moments of the electron orbitals of these ions, which results in non-vanishing polarization for certain spin configurations. The approach accounts for the macroscopic symmetry of the unit cell and is valid both for commensurate and complex incommensurate magnetic structures. The model is illustrated by the examples of MnWO4, MnPS3 and LiNiPO4. Application to other magnetoelectrics is discussed.Comment: 11 pages, 2 figures, 2 table

Формирование покрытий смешанными оксидами алюминия и марганца на сплаве АЛ25

Features of plasma electrolytic oxidation of the AL25 cast complex-alloyed aluminum alloy are discussed. It has been shown that a variation in the nature and concentration ratio of the electrolyte components provides the formation of mixed-oxide coatings containing the materials of the basic matrix and the dopant. An increase in the coating thickness and the manganese oxide content in the coating is achieved by the homogenization of the treated surface owing to the simultaneous formation of oxides and the removal of alloying components of the alloy from the surface layers. Current density intervals that provide a uniform distribution of elements in the coating and a high efficiency of the Faraday and thermochemical reactions are determined. It is found that the stoichiometric oxygen index in MnOx oxides is x = 1.71–1.87. Testing of the synthesized oxide systems in the model oxidation of carbon (II) oxide to CO₂ shows that the ignition and complete conversion temperatures are at the level of values characteristic of platinum catalysts.Рассмотрены особенности плазменно-электролитического оксидирования литейного сложнолегированного сплава алюминия АЛ25. Показано, что варьирование природы и соотношения концентраций компонентов электролита позволяет формировать покрытия смешанными оксидами, в состав которых входит материал основной матрицы и допанта. Повышение толщины покрытия и содержания в нем оксида марганца достигается гомогенизацией обрабатываемой поверхности за счет одновременного формирования оксидов и удаления легирующих компонентов сплава из поверхностных слоев. Установлены интервалы плотности тока, обеспечивающие равномерное распределение элементов в покрытии и высокую эффективность фарадеевских и термохимических реакций. Показано, что стехиометрический индекс по кислороду в оксидах MnOx составляет x = 1,71–1,87. Тестирование синтезированных оксидных систем в модельной реакции окисления оксида углерода (II) до CO₂ показало, что температура зажигания и полной конверсии находится на уровне платиновых катализаторов

Гальванохімічне формування багатокомпонентного сплаву на основі кобальта та тугоплавких металів

Effects of major parameters of electrolysis on the composition and morphology of the cobalt-molybdenum-tungsten alloy from citrate- pyrophosphate and citrate-ammonium electrolytes have been analysed. It has been shown that the content of component metals in the Co-W-Mo alloy depends on the nature and composition of the electrolyte solution. The influence of electrolysis conditions and regime on the structure and morphology of cobalt alloys with refractory metals has been established. The elemental composition and morphology of the triple cobalt - molybdenum - tungsten coatings have been determined with a scanning electron microscope.Проаналізовано вплив основних параметрів електролізу на склад та морфологію сплаву кобальт-молібден-вольфрам отриманого з цитратно-дифосфатного та цитратно-амоніачного електролітів. За допомогою сканівного електронного мікроскопу досліджено склад і морфологію потрійних покриттів. Було показано, що вміст компонентів в сплаві Со-W-Мо залежить від природи ліганда і співвідношення концентрацій сплавотвірних металів. Встановлено вплив густини струму, а також часу імпульсу та паузи на структуру і морфологію покриттів

Electrodeposition of iron-molybdenum coatings from citrate electrolyte

Specifi c features of the electrodeposition of iron–molybdenum coatings from a citrate electrolyte based on iron(III) sulfate and sodium molybdate in dc and unipolar pulsed modes were studied. It was demonstrated that bright compact coatings with varied content of molybdenum can be produced by varying the relative concentrations of salts of the alloy-forming components and the solution pH. The current density ranges providing the high efficiency of the galvanostastic electrolysis were determined and it was shown that using the pulsed mode makes smaller the amount of nonmetallic impurities in a coating, diminishes its roughness and leads to formation of surface layers with a more uniform composition, The iron–molybdenum coatings exhibit a high corrosion resistance in corrosive media and physicomechanical properties improved as compared with the base metal, which makes it possible to recommend these coatings for protection from corrosive-mechanical disintegration and restoration of the surface of worn articles

Mixed alumina and cobalt containing plasma electrolytic oxide coatings

Principles of plasma electrolytic oxidation of the AL25 aluminum alloy in diphosphate alkali solutions containing cobalt(2+) cations are discussed. It has been established that a variation in the concentration of the electrolyte components provides the formation of mixed-oxide coatings consisting of the basic matrix materials and the cobalt oxides of different content. An increase in the cobalt oxide content in the coating is achieved by the variation in electrolysis current density as well as the treatment time due to both the electrochemical and thermo-chemical reactions at substrate surface and in spark region. Current density intervals that provide micro-globular surface formation and uniform cobalt distribution in the coating are determined. The composition and morphology of the surface causes high catalytic properties of synthesized materials, which confirmed the results of testing in model reaction CO and benzene oxidation as well as fuel combustion for various modes of engine operation

Функциональные свойства гальванических сплавов Fe−Mo и Fe−Mo−W

The influence of the modes of electrodeposition on the morphology, topography, and structure of the galvanic alloys of iron with molybdenum and tungsten is discussed. It is shown that the increase in the corrosion resistance of Fe–Mo and Fe–Mo–W coatings in acid and neutral chloride-containing media is caused both by the elevation of their passivating ability caused by the process of alloying components and by the formation of globular surfaces with homogeneous chemical composition. The microhardnesses of Fe–Mo and Fe–Mo–W galvanic alloys prove to be 2–3 times higher than the microhardnesses of the substrates made of low-alloy steel, which can be explained by the formation of amorphous structures. The results of investigations and tribological tests show that it is reasonable to apply the coatings of double and triple iron alloys in order to reduce wear in friction couples and to increase the corrosion resistance and mechanical strength of the surfaces, which makes them promising for the repair and restoration technologies.Изучено влияние методов электроосаждения на морфологию, топографию и структуру гальванических сплавов железа с молибденом и вольфрамом. Показано, что рост коррозионной стойкости покрытий Fe–Mo и Fe–Mo–W в кислых и нейтральных хлоридсодержащих средах обусловлен увеличением их способности к пассивации в присутствии легирующих компонентов и формированием глобулярной равномерной по составу поверхности. Микротвердость гальванических сплавов Fe–Mo и Fe–Mo–W возрастает в 2-3 раза по сравнению с показателем подложки из низколегированной стали за счет формирования аморфной структуры. Результаты исследований и трибологических тестов показали целесообразность применения двойных и тройных сплавов железа для снижения износа в парах трения и увеличения коррозионного сопротивления и механической прочности поверхностей, что делает их привлекательными для технологий восстановления и упрочнения поверхностей