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

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

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

Biological diversity of the coastal zone of the Crimean peninsula: problems, preservation and restoration pathways

The results of complex hydrochemical, hydrobiological and ichthyological investigations by IBSS, NAS of Ukraine, realized in 6 regions of the coastal zone of the Crimean peninsula in the Black Sea and the Sea of Azov are given. The main negative factors causing changes in structural and functional characteristics of hydrobiocenoses in the regions studied are analyzed and “hot ecological spots” are isolated. Variants of different methods of management of the coastal ecosystems, including construction of artificial reefs and usage of biological filters for water cleaning, protection and recreation of biological diversity are taken into consideration

Practical Implementation of the Algorithm for Processing Signals Obtained by Magnetic Flaw Detection of Rolled Steel

Various mathematical methods are used to process the signals obtained by using magnetic flaw detection of rolled steel. In the article [1], a method for increasing the resolution of magnetic flaw detection is proposed. © 2022 American Institute of Physics Inc.. All rights reserved.Minobrnauki of Russia, (AAAA-A18-118020690196-3)The research was carried out within the state assignment of Minobrnauki of Russia (theme “Diagnostics” No. AAAA-A18-118020690196-3)

Recommendations for the Repair of Gas Pipeline Sections Containing SCC Defects Up to 10% of the Pipe Wall Depth

The SCC problem remains discussed until now, despite 40 years of research. The approaches to SCC of scientific organizations to defects up to 10% deep are considered. The mechanism of development depending on soil pH is described. Measures are proposed taking into account the acidity of the soil. © 2022 American Institute of Physics Inc.. All rights reserved.Ural Branch, Russian Academy of Sciences, UB RASThe work was performed within the state assignment on the subjects Diagnostics (No. AAAA-A18-118020690196-3) and supported by a UB RAS Program project

Characteristics of neutrophilic granulocytes of peripheral blood in patients with mechanical jaundice caused by cholangiocarcinoma

Obstructive jaundice caused by cholangiocarcinoma takes a special place among malignant disorders and surgical pathology in Russia. Involvement of nonspecific immunity and the role of neutrophils in carcinogenesis are ambiguously evaluated. The aim of this study was to study functional activity of peripheral blood neutrophilic granulocytes and their phenotype in obstructive jaundice caused by cholangiocarcinoma. The study included 56 patients with obstructive jaundice associated with cholangiocarcinoma at the T2- 3N0- 1M0 stage (clinical stages II-III), and 90 apparently healthy volunteers of similar age group. Neutrophilic granulocytes were isolated from peripheral blood by means of double-density Ficoll-Urografin gradient.Venous blood was collected in patients into vacutainers with heparin upon admission to the hospital, before the surgery was performed. Spontaneous cytokine production (IL-8, IFNá) was determined by enzyme-linked immunosorbent assay using Vector-Best diagnostic kits. To assess phagocytic activity of neutrophilic granulocytes, the phagocytic index (according to Hamburger), number of phagocytes (according to Wright) and the index of completed phagocytosis (according to Rudik, 2006) were calculated. Immunophenotyping of neutrophilic granulocytes was carried out using an FC500 flow cytometer (Beckman Coulter, USA) with monoclonal antibodies to CD11b+, CD16+, CD95+. The results were statistically analyzed using the Statistica v.12.0 software (StatSoft Inc., USA). To assess intergroup differences, the nonparametric Kruskal-Wallis tests (for three or more comparison groups) and Mann-Whitney tests (for pairwise comparison) were used. Comparison of groups for a qualitative binary trait was carried out using the two-sided Fisher’s exact test. Data are presented as Median (25 quartile-75 quartile).The study of the functional activity of peripheral blood neutrophiles in obstructive jaundice patients caused by cholangiocarcinoma revealed an increase in their relative and absolute number, increased phagocytic index and decreased phagocytic number of neutrophilic granulocytes, increased expression of CD11b+, CD16+, CD95+ immunological markers. The changes in neutrophil secretory activity were characterized by a decrease in cytokine production (IL-2, IFNá). An increase in functional activity of neutrophilic granulocytes, along with a decrease in their cytokine production suggests that, in obstructive jaundice observed in cholangiocarcinoma at clinical stage T2-3N0-1M0, an equilibrium stage is revealed between the cells of immune system and malignant tumor

W- rich mixed oxide solid solutions under pressure

We report high-pressure synchrotron X-ray powder diffraction data for the W-rich cubic ZrW[2-x]Mo[x]O[8] (x=0.4) up to 10 GPa with open decompression. This study shows that cubic- ZrW[1.6]Mo[0.4]O[8] transforms to orthorhombic phase at the 5.04 GPa. Pressure-induced reversable amorphization of material was observed at 8.13 GPa. The obtained data suggest that W-rich cubic ZrW[2-x]Mo[x]O[8] (x=0.4) solid solutions are more attractive for creating products working under extreme conditions and mechanic stress