Electron energy spectrum and magnetic interactions in high-T(sub c) superconductors

The character of magnetic interactions in La-Sr-Cu-O and Y-Ba-Cu-O systems is of primary importance for analysis of high-T(sub c) superconductivity in these compounds. Neutron diffraction experiments showed the antiferromagnetic ground state for nonsuperconducting La2CuO4 and YBa2Cu3O6 with the strongest antiferromagnetic superexchange being in the ab plane. The nonsuperconducting '1-2-3' system has two Neel temperatures T sub N1 and T sub N2. The first one corresponds to the ordering of Cu atoms in the CuO2 planes; T sub N2 reflects the antiferromagnetic ordering of magnetic moments in CuO chains relatively to the moments in the planes T sub N1 and T sub N2 depend strongly on the oxygen content. Researchers describe magnetic interactions in high-T superconductors based on the Linear Muffin-Tin Orbitals (LMTO) band structure calculations. Exchange interaction parameters can be defined from the effective Heisenberg hamiltonian. When the magnetic moments are not too large, as copper magnetic moments in superconducting oxides, J sub ij parameters can be defined through the non-local magnetic susceptibility of spin restricted solution for the crystal. The results of nonlocal magnetic susceptibility calculations and the values of exchange interaction parameters for La CuO and YBa2Cu3O7 systems are given in tabular form. Strong anisotropy of exchange interactions in the ab plane and along the c axis in La2CuO4 is obviously seen. The value of Neel temperature found agrees well with the experimental data available. In the planes of '1-2-3' system there are quite strong antiferromagnetic Cu-O and O-O interaction which appear due to holes in oxygen subbands. These results are in line with the magnetic model of oxygen holes pairing in high-T(sub c) superconductors

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

Radial basis approximation of single-phase flow in porous media based on the Green’s functions

The article discusses the problem of approximating solutions of differential equations describing the process of a two-dimensional fluid flow in porous media. The approximation is presented as a combination of radial basis functions on the basis of the Green’s function is used to solve the Poisson equation with variable coefficients in the case of steady state filtration and parabolic equations in the transient regime. To illustrate the effectiveness of the proposed approximation obtained by the field pressure distribution in the reservoir with a network of injection and production wells. Compare approximated pressure and design points to a satisfactory accuracy of the results

Building surrogate models for two-phase flow of fluids in porous media based on spatial radial basis approximation

The paper proposes a method for constructing the surrogate models for two-phase flow based on a combination of finite-difference solutions and fine-grid spatial approximation. The method provides the approximate models for solving optimal control the operating parameters of field development

Social networks as a basis for interaction between authorities and non-profit organizations established on the basis of nationality in public communications space

The article is devoted to the discussion of the influence of modern information and telecommunication technologies on the process of building bilateral communication of state and municipal administration bodies with non-profit organizations created on the basis of national origin from the point of view of the management of public values and the stakeholder approach. The purpose of this article is to analyse the possibilities of organizing social and network interaction between the authorities and representatives of non-profit organizations as an institutionalized form of existence of national communities and faiths (on the example of social and network space of public communications of the Central Federal District). In the course of the study it was found that in the sphere of interethnic and interethnic relations the most relevant is the formation of a specialized single social and network resource in the information and communication space of the region. The preferred format of using such a resource, according to experts, should be related to the questions of obtaining information on decisions made by the authority and their subsequent discussion. At the same time, experts underestimate the possibilities of organizing dialogue and partnership on the basis of social media. At the same time, an analysis of existing social media practices has shown 1) a small proportion of accounts of state structures, which are responsible for interaction with representatives of national associations and diasporas; 2) the mismatch distribution in the social and network space of public communications pages of the authorities of the subject of the Russian Federation, carrying out in their activities interaction with national NGOs, accounts of non-profit organizations themselves, created on the basis of national origin, as well as representatives of national communities and diasporas. These circumstances allowed the authors to make a conclusion that it is necessary to establish in social networks systematic work of the authorities of the constituent entities of the Russian Federation with non-profit organizations, which represent national diasporas and communities on the territory of the regions of the Central Federal District

Social media as dialogue platforms for citizens and authorities of the Central Federal District's entities

This study examines the role of social and network resources in building dialogue with citizens on the example of subjects of the Central Federal District of regional government bodies. The study is based on monitoring the network space of public communications formed around the accounts of the authorities of the subjects of the Central Federal District. The data obtained were compared with the results of similar monitoring in 2019, as well as the results of a sociological survey on civic engagement of the population on social networks.As a general rule, the presence of two key network resources in each of the regions was noted – the personal accounts of the head of the region and the official pages of governments (administrations). These resources act as a network “showcase”, are efficiently administered and are consistently filled with well-developed content. Monitoring data make it possible to confirm the presence in the network space of public communications of a fully developed pool of government accounts in popular social media users among domestic Internet users of social media. But at the same time, a decrease in user involvement in the socio-network space of public communications around government accounts is observed for all regions under study.The information field of each region of the Central Federal District is unique, its actual structure depends on a number of objective factors, such as the level of penetration of various social networks into the audience of Internet users, the activity of large network actors (bloggers, media, popular public), the features of network interaction of ordinary users. Ultimately, the totality of external conditions should predetermine the model of behavior of authorities in social networks.The introduction of the “Incident Management” system has had a positive impact on the situation, through which citizens’ appeals are not only accepted and processed, but also sent to target authorities, which are obliged to provide a response to the applicant via social networks.The conclusion of the study presents the authors’ recommendations, which, in our opinion, will optimise the operation of the network of official accounts of the entities of the Central Federal District

Electron energy spectrum and magnetic interactions in high-Tc superconductors

The character of magnetic interactions in La-Sr-Cu-O and Y-Ba-Cu-O systems is of primary importance for analysis of high-T(sub c) superconductivity in these compounds. Neutron diffraction experiments showed the antiferromagnetic ground state for nonsuperconducting La2CuO4 and YBa2Cu3O6 with the strongest antiferromagnetic superexchange being in the ab plane. The nonsuperconducting '1-2-3' system has two Neel temperatures T(sub N1) and T(sub N2). The first one corresponds to the ordering of Cu atoms in the CuO2 planes; T(sub N2) reflects the antiferromagnetic ordering of magnetic moments in CuO chains relatively to the moments in the planes T(sub N1) and T(sub N2) which depend strongly on the oxygen content. Researchers describe magnetic interactions in high-T superconductors based on the Linear Muffin-Tin Orbitals (LMTO) band structure calculations. Exchange interaction parameters can be defined from the effective Heisenberg Hamiltonian. When the magnetic moments are not too large, as copper magnetic moments in superconducting oxides, J(sub ij) parameters can be defined through the non-local magnetic susceptibility of spin restricted solution for the crystal. The results of nonlocal magnetic susceptibility calculations and the values of exchange interaction parameters for La CuO and YBa2Cu3O7 systems are given in tabular form. Strong anisotropy of exchange interactions in the ab plane and along the c axis in La2CuO4 is obviously seen. The value of Neel temperature found agrees well with the experimental data available. In the planes of '1-2-3' system there are quite strong antiferromagnetic Cu-O and O-O interaction which appear due to holes in oxygen subbands. These results are in line with the magnetic model of oxygen holes pairing in high-T(sub c) superconductors

Building and optimizing a model of low level for two-phase filtration

The paper proposes a method for constructing models of low level for two-phase flow based on a combination of finite-difference solutions and detailed spatial approximation, providing the possibility of approximating the models for solving optimal control the operating parameters of the oil reservoir

Solving optimization problems of optimal control of operational parameters of oil reservoir

The paper proposes a method for solving optimal control operating parameters of oil stratum: the arrangement of injection and production wells; regulation works well in setting of the two-phase filtration. Depending on the optimization of the planning horizon on the basis of the proposed method gives the prediction of increasing production by 27 % in the long-term planning up to 60 % for short-term planning

Strong short-range magnetic order in a frustrated FCC lattice and its possible role in the iron structural transformation

We investigate magnetic properties of a frustrated Heisenberg antiferromagnet with a face-centered cubic (FCC) lattice and exchange interactions between the nearest- and next-nearest neighbours, J1 and J2. In a collinear phase with the wave vector Q = (pi,pi,pi) the equations of the self-consistent spin-wave theory for the sublattice magnetization and the average short range order parameter are obtained and numerically solved. The dependence of the Neel temperature T_N on the ratio J2/J1 is obtained. It is shown, that at strong enough frustration there is a wide temperature region above T_N with strong short range magnetic order. Application of this result to description of structural phase transition between alpha and gamma-phase of Fe is considered