Crystal chemical and quantum chemical studies of Ba(Sr)-Nb oxide compounds

The information available on the BaO(SrO)-NbO-NbO2 system with the niobium atom in the lower oxidation degree is very limited. Very few compounds have been found previously in this system. They are BaNbO3, SrxNbO3(0,7=x=1), Ba2Nb2O9, SrNb8O14; and some suggestions on the BaNb8O14 existence have been made also. At the same time Nb-based oxide compounds could be quite interesting in the search of new noncopper high T(sub c) superconductors Researchers studied Ba(Sr) NbxO2x-2 and Ba2(Sr2)-NbxO2x-1 compositions in the phase diagram of BaO(SrO)-NbO-NbO2 system. The synthesis of the materials was carried out in vacuum at the temperatures of 1000 to 1500 C. Barium carbonate and niobium pentoxide were used as initial components. X-ray analysis was carried out

Frustration phenomena in Josephson point contacts between single-band and three-band superconductors

Within the formalism of Usadel equations the Josephson effect in dirty point contacts between single-band and three-band superconductors is investigated. The general expression for the Josephson current, which is valid for arbitrary temperatures, is obtained. We calculate current-phase relations for very low temperature and in the vicinity of the critical temperature. For three-band superconductors with broken time-reversal symmetry (BTRS) point contacts undergo frustration phenomena with different current-phase relations, corresponding to {\phi}-contacts. For three-band superconductors without BTRS we have close to sinusoidal current-phase relations and absence of the frustration, excepting the case of very low temperature, where under certain conditions two ground states of the point contact are realized. Our results can be used as the potential probe for the detection of the possible BTRS state in three-band superconducting systems.Comment: 14 pages, 7 figure

Експериментальні та теоретичні дослідження таутомерії серед 3-заміщених 2-метилхінолін-4(1H)-онів

4-Hydroxy-/4-oxo tautomerism in the series of 3-substituted 2-methyl-quinolin-4(1H)-ones has been studied by 13C NMR-spectroscopy and quantum-chemical methods in various approximations (restricted Hartree-Fock method, DFT and MP2) for the isolated molecules and for solutions using empirical correction of effects for solvents (PCM COSMO procedure). Substituents that are different in their nature have no significant influence on the value of the chemical shift of carbon in position C4 of the quinolone cycle. The only exception is the carbon shielding associated with the bromine atom in the molecule of 3-bromo-2-methyl-1,4-dihydroquinoline-4-one. Significant deshielding detected in all cases in 13C NMR-spectra of the carbon nuclei in position 4 of the ring is in favour of the existence of all derivatives studied as 4-oxo forms in DMSO-d6 solution. The experimental and calculated values for the chemical shift of carbon in position C4 of 4-oxo and 4-hydroxy isomers differ considerably and can be used as a criterion for assigning quinolin-4 (1H)-ones to a particular tautomeric form.С помощью ЯМР 13С спектроскопии и квантово-химическими методами в различных приближениях (ограниченный метод Хартри-Фока, DFT и МР2) для изолированных молекул и растворов с использованием эмпирической коррекции эффектов растворителей (процедура РСМ COSMO) исследована 4-гидрокси 4-оксо-таутомерия в ряду производных 3-замещенных 2-метилхинолин-4(1Н)-онов. Различные по своему характеру заместители не оказывают существенного влияния на значение химического сдвига углерода в положении С4 хинолонового цикла. Исключение составляет лишь экранирование углерода, связанного с атомом брома в молекуле 3-бромо-2-метил-1,4-дигидрохинолин-4-oна. Значительное дезэкранирование, обнаруженное во всех случаях в спектрах ЯМР 13С для ядер углерода в 4-ом положении кольца, говорит в пользу существования всех исследованных производных в растворе в DMSO-d6 в виде 4-оксо-форм. Экспериментальные и расчетные значения химического сдвига для углерода в положении С4 для 4-оксо- и 4-гидрокси-изомеров заметно отличаются и могут быть использованы в качестве критерия для отнесения хинолин-4(1Н)-онов к той или иной таутомерной форме.За допомогою ЯМР 13С спектроскопії і квантово-хімічними методами в різних наближеннях (обмежений метод Хартрі-Фока, DFT і МР2) для ізольованих молекул і розчинів з використанням емпіричної корекції ефектів розчинників (процедура РСМ COSMO) досліджена 4-гідрокси оксо-таутомерія в ряду похідних 3-заміщених 2-метилхінолін-4(1Н)-онів. Різні за своїм характером замісники не чинять істотного впливу на значення хімічного зсуву вуглецю в положенні С4 хінолонового циклу. Виняток становить лише екранування вуглецю, пов’язаного з атомом брому в молекулі 3-бромо-2-метил-1,4-дигідрохінолін-4-oну. Значне дезекранування виявлене у всіх випадках у спектрах ЯМР 13С для ядер вуглецю в 4-му положенні кільця вказує на користь існування всіх досліджених похідних у розчині в DMSO-d6 у вигляді 4-оксо-форм. Експериментальні та розрахункові значення хімічного зсуву для вуглецю в положенні С4 для 4-оксо- і 4-гідрокси-ізомерів помітно відрізняються і можуть бути використані в якості критерію для віднесення хінолін-4 (1Н)-онів до тієї чи іншої таутомерної форми

Синтез і комп’ютерний скринінг нових 2-метилхінолін-4-онів, зв’язаних з піразолон-5-оновим фрагментом

The 1,3-dicarbonyl derivatives of 2-methyl-1,4-dihydroquinoline-4-one have been synthesized by alkylation of methylene active compounds with 3-dimethylaminomethyl-2-methyl-1,4-dihydroquinoline-4-one. These compounds are the convenient starting material for creating the new chemical libraries in the series of 3-heteryl substituted 2-methyl-1,4-dihydroquinoline-4-ones. In this work the examples of the synthesis of new quinolone-pyrazolone systems are presented. Their condensation with hydrazine hydrate resulted in the new derivatives of 2-methyl-3-[(5-oxo-4,5-dihydro-1H-pyrazol-4-yl)methyl]-1,4-dihydroquinolin-4-ones. The estimation of novelty of the compounds obtained in such chemical databases as PubChem, ChemBl, Spresi has shown that these substances are not present in these sources, and the chemical scaffold – quinolone bound via the methylene bridge with azoles is new. Determination of 2D similarity of the compounds synthesized by standard molecular descriptors with the biologically active structures in the ChemBl_20 database has shown the uniqueness of a new quinolone scaffold and the potential anti-inflammatory activity for compounds of this series. The molecular similarity has been determined using the ChemAxon software (JKlustor, Instant JChem).Алкилированием 3-диметиламинометил-2-метил-1,4-дигидрохинолин-4-оном метиленактивных соеди- нений были синтезированы 1,3-дикарбонильные производные 2-метил-1,4-дигидрохинолин-4-она. Дан- ные соединения являются удобным стартовым материалом для создания библиотек в ряду 3-гетерилзамещенных 2-метил-1,4-дигидрохинолин-4-онов. В работе приведены примеры синтеза новых хинолон-пиразолоновых систем. Конденсацией алкилированных метиленактивных соединений с гидразин гидратом получены новые производные 2-метил-3-[(5-оксо-4,5-дигидро-1H-пиразол-4-ил)метил]-1,4- дигидрохинолин-4-онов. Проведенная оценка новизны полученных соединений по химическим базам PubChem, ChemBl и Spresi показала, что данные соединения совсем не представлены в этих источниках, а химический скаффолд – хинолон, соединенный через метиленовый мостик с азолами, является новым. Определение 2D подобия синтезированных соединений по стандартным молекулярным дескрипторам с биологически активными структурами базы данных ChemBl_20 показало уникальность и перспективность нового хинолонового скаффолда в дизайне лекарственных веществ, а также вероятность проявления противовоспалительной активности среди соединений данного ряда. Молекулярное подобие было определено с помощью программного обеспечения ChemAxon (JKlustor, Instant JChem).Алкілуванням 3-диметиламінометил-2-метил-1,4-дигідрохінолін-4-оном метиленактивних сполук були синтезовані 1,3-дикарбонільні похідні 2-метил-1,4-дигідрохінолін-4-ону. Дані сполуки є зручним стар- товим матеріалом для створення хімічних бібліотек в ряду 3-гетерилзаміщених 2-метил-1,4-ди- гідрохінолін-4-онів. У роботі наведені приклади синтезу нових хінолон-піразолонових систем. Конден- сацією алкілованих метиленактивних сполук з гідразин гідратом отримані нові похідні 2-метил-3-[(5- оксо-4,5-дигідро-1H-піразол-4-іл)метил]-1,4-дигідрохінолін-4-онів. Проведена оцінка новизни отриманих сполук за хімічними базами PubChem, ChemBl і Spresi показала, що дані сполуки зовсім не представлені в цих джерелах; а хімічний скаффолд – хінолон, з’єднаний через метиленовий місток з азолами, є новим. Визначення 2D схожості синтезованих речовин за стандартними молекулярними дескрипторами з біологічно активними структурами бази даних ChemBl_20 показало унікальність і перспективність нового хінолонового скаффолда в дизайні лікарських речовин, а також імовірність прояву протизапальної активності серед сполук даного ряду. Молекулярну схожість було визначено за допомогою програмного забезпечення ChemAxon (JKlustor, Instant JChem)

Precision determination of band offsets in strained InGaAs/GaAs quantum wells by C-V-profiling and Schroedinger-Poisson self-consistent simulation

The results of measurements and numerical simulation of charge carrier distribution and energy states in strained quantum wells In_xGa_{1-x}As/GaAs (0.06 < x < 0.29) by C-V-profiling are presented. Precise values of conduction band offsets for these pseudomorphic QWs have been obtained by means of self-consistent solution of Schroedinger and Poisson equations and following fitting to experimental data. For the conduction band offsets in strained In_xGa_{1-x}As/GaAs - QWs the expression DE_C(x) = 0.814x - 0.21x^2 has been obtained.Comment: 9 pages, 12 figures, RevTeX

Influence of the axial compressor blade row defects on the industrial gas turbine performance

This paper presents the compressor blade algorithm for predicting the defect influence on the characteristics of the stage, axial compressor or GTU as a whole. The developed model is based on the use of Bezier curves, with the control point coordinates calculated using the main geometric parameters of the airfoil, which provides highly precise geometry of both the airfoil and the blade as a whole. The paper shows some results of verification of the developed method and the selected numerical model parameters, as well as the analysis of the defect influence on the airfoil flow conditions in order to demonstrate the capabilities of the algorithm. The main results of the study were summarized and recommendations for further research were developed. © 2020 Institute of Physics Publishing. All rights reserved

Lattice Distortion and Magnetism of 3d-t2gt_{2g} Perovskite Oxides

Several puzzling aspects of interplay of the experimental lattice distortion and the the magnetic properties of four narrow $t_{2g}$-band perovskite oxides (YTiO$_3$, LaTiO$_3$, YVO$_3$, and LaVO$_3$) are clarified using results of first-principles electronic structure calculations. First, we derive parameters of the effective Hubbard-type Hamiltonian for the isolated $t_{2g}$ bands using newly developed downfolding method for the kinetic-energy part and a hybrid approach, based on the combination of the random-phase approximation and the constraint local-density approximation, for the screened Coulomb interaction part. Then, we solve the obtained Hamiltonian using a number of techniques, including the mean-field Hartree-Fock (HF) approximation, the second-order perturbation theory for the correlation energy, and a variational superexchange theory. Even though the crystal-field splitting is not particularly large to quench the orbital degrees of freedom, the crystal distortion imposes a severe constraint on the form of the possible orbital states, which favor the formation of the experimentally observed magnetic structures in YTiO$_3$, YVO_, and LaVO$_3$ even at the HF level. Beyond the HF approximation, the correlations effects systematically improve the agreement with the experimental data. Using the same type of approximations we could not reproduce the correct magnetic ground state of LaTiO$_3$. However, we expect that the situation may change by systematically improving the level of approximations for dealing with the correlation effects.Comment: 30 pages, 17 figures, 8 tables, high-quality figures are available via e-mai

Approach for the Modelling of the Compressor's Defective Blades with Numerical Simulation Methods

The current work presents the intermediate results of model development to assess the impact of various defects on the axial compressor operation. Recommendations for adjusting computational models are proposed to conduct gas-dynamic and strength studies of compressor stages and blades, taking into account various defects: verification for the presented models was carried out, which results are also presented in the paper. Based on the verification calculations results some features of CFD modeling are considered, as well as requirements for the investigated defects are indicated. The Discussion section presents the defects classification according to their influence on the compressor operation, which studying is possible using a specially developed mathematical description of blade profiles and blades geometry, as well as considering all the recommendations for computational model adjusting and a general approach to blades modeling defects. © 2022 Institute of Physics Publishing. All rights reserved

On the non-Abelian Stokes theorem for SU(2) gauge fields

We derive a version of non-Abelian Stokes theorem for SU(2) gauge fields in which neither additional integration nor surface ordering are required. The path ordering is eliminated by introducing the instantaneous color orientation of the flux. We also derive the non-Abelian Stokes theorem on the lattice and discuss various terms contributing to the trace of the Wilson loop.Comment: Latex2e, 0+14 pages, 3 figure

Neutron diffraction study of YVO3, NdVO3, and TbVO3

The structural and magnetic properties of YVO3, NdVO3 and TbVO3 were investigated by single-crystal and powder neutron diffraction. YVO3 shows a structural phase transition at 200 K from an orthorhombic structure with the space group Pbnm to a monoclinic one with the space group P21/b. But supplementary high-resolution synchrotron diffraction experiments showed that the monoclinic distortion is extremely small. A group theoretical analysis shows that this magnetic state in the monoclinic phase is incompatible with the lattice structure, unless terms of higher than bilinear order in the spin operators are incorporated in the spin Hamiltonian. This observation is discussed in the light of recent theories invoking unusual many-body correlations between the vanadium t2g orbitals. A structural phase transition back to the orthorhombic space group Pbnm is observed upon cooling below 77 K. This transition is accompanied by a rearrangement of the magnetic structure into a mode compatible with the lattice structure. The crystal structures of NdVO3 and TbVO3 are closely similar to that of YVO3. However, only a single magnetic phase transition was found in the vanadium sublattice down to 9.5 K. Below 60 K the magnetic moments of the Nd- and Tb-ions are gradually polarized by the ordered vanadium moments. Below 11 K, we found a noncollinear order of the terbium moments