Correlation effects in the ground state charge density of Mott-insulating NiO: a comparison of ab-initio calculations and high-energy electron diffraction measurements

Accurate high-energy electron diffraction measurements of structure factors of NiO have been carried out to investigate how strong correlations in the Ni 3d shell affect electron charge density in the interior area of nickel ions and whether the new ab-initio approaches to the electronic structure of strongly correlated metal oxides are in accord with experimental observations. The generalized gradient approximation (GGA) and the local spin density approximation corrected by the Hubbard U term (LSDA+U) are found to provide the closest match to experimental measurements. The comparison of calculated and observed electron charge densities shows that correlations in the Ni 3d shell suppress covalent bonding between the oxygen and nickel sublattices.Comment: 6 pages, LaTeX and 5 figures in the postscript forma

Частотно-перестраиваемое устройство на основе многослойного полосково-щелевого перехода и его применение для измерения диэлектрических свойств материалов

The paper presents the results of theoretical and experimental researches of a frequency-tunable device based on the multilayer strip-slot transition with the U-shaped slot resonator of the variable length. The application of the presented device makes it possible to implement a resonant method for measuring the dielectric properties of materials in the microwave frequency range. The numerical simulation in the rigorous formulation of the electrodynamics problem is performed for the theoretical research. The aim of the theoretical research is to determine the electrical characteristics of the multilayer strip-slot transition with the U-shaped slot resonator of the variable length. The results of numerical simulation prove the possibility of applying the multilayer stripslot transition with the U-shaped slot resonator of the variable length to implement the resonant method for measuring the dielectric properties of materials in the microwave frequency range. The experimental research is performed on the sample of the multilayer strip-slot transition with the U-shaped slot resonator of the variable length in the frequency range (850–1250) MHz. Measurements of S-parameters of the multilayer strip-slot transition with the U-shaped slot resonator of the variable length are accomplished using the vector network analyzer. The material under research is BaFe10Ti2O19. The results of theoretical and experimental researches are in good qualitative and quantitative agreement. Представлены результаты теоретических и экспериментальных исследований частотно-перестраиваемого устройства на основе многослойного полосково-щелевого (МПЩ) перехода с П-образным щелевым резонатором. Использование данного устройства позволяет реализовать резонансный метод измерения диэлектрических свойств материалов в сверхвысокочастотном диапазоне. Теоретические исследования заключаются в проведении численного моделирования в строгой постановке электродинамической задачи, направленной на определение характеристик МПЩ-перехода с П-образным щелевым резонатором переменной длины. Результаты численного моделирования доказывают возможность применения МПЩ-перехода с П-образным щелевым резонатором переменной длины для реализации резонансного метода измерения диэлектрических свойств материалов в указанном диапазоне частот. Экспериментальные исследования проведены на макете МПЩ-перехода с П-образным щелевым резонатором переменной длины в диапазоне частот (850–1250) МГц. Оценка его резонансных свойств осуществлялась при использовании векторного анализатора цепей OBZOR TR1300/1. В качестве исследуемого материала использовался материал BaFe10Ti2O19. Результаты теоретических и экспериментальных исследований находятся в хорошем количественном и качественном согласовании. Фомин Д. Г., Дударев Н. В., Даровских С. Н. Частотно-перестраиваемое устройство на основе многослойного полосково-щелевого перехода и его применение для измерения диэлектрических свойств материалов. Ural Radio Engineering Journal. 2021;5(3):225–238. DOI: 10.15826/urej.2021.5.3.002.

ADAPTING PORTAL DECOMPRESSION FOR ELEVATION OF EFFICACY OF PORTOSYSTEMIC SHUNTING OPERATIONS IN PORTAL HYPERTENSION

Purpose: to improve the results of portosystemic shunting surgical interventions using of procedures of adapting portal decompression during preoperation period. Materials and Methods: the results of transjugular intrahepatic portosystemic shunt (TIPS procedure) in 113 patients were analyzed. In 60 cases the procedure of adapting portal decompression during a period 3-5 weeks using selective vasoconstrictor octreotide in complex with non-selective beta-blockers.Results: during the follow-up postoperative period in group of patients who were undergone for adapting portal decompression the restitution of clinical and laboratory data was noticed and does not increase occurrence of hepatic insufficiency in comparison with control group.Summary: using of adapting portal decompression in preoperative period before TIPS procedure in patients with complicated portal hypertension is effective for prophylaxis of making worse of hepatic insufficiency

Сardiac arrhythmias in people who have had a coronavirus infection COVID-19: A review

Heart rhythm disorders are one of the most common complications of coronavirus infection. Heart rhythm disorders can develop in 6–17% of hospitalized patients, and in convalescents, COVID-19 can manifest itself up to 12 months after the completion of the acute phase of the disease. Among the mechanisms for the development of cardiac arrhythmias, there are a direct cytopathic effect of SARS-CoV-2 on the myocardium, systemic inflammatory response syndrome, electrolyte imbalance, hypoxia, the use of antibacterial, antimalarial and antiviral drugs, exudative pericarditis, autonomic dysfunction. The main COVID-19-mediated heart rhythm disorders are sinus tachycardia and bradycardia, atrial fibrillation, ventricular tachycardia, long QT syndrome. Despite a significant amount of research, the literature data on the prevalence of certain types of cardiac arrhythmias (especially in COVID-19 convalescents), as well as methods for their correction, are somewhat contradictory and need to be clarified. Taking into account the impact of arrhythmia on the quality of life and mortality, active monitoring of convalescents of coronavirus infection, identification and development of approaches to the treatment of heart rhythm disorders in patients who have had COVID-19, seem to be relevant and promising areas in modern cardiology

Implementation of the Projector Augmented Wave LDA+U Method: Application to the Electronic Structure of NiO

The so-called local density approximation plus the multi-orbital mean-field Hubbard model (LDA+U) has been implemented within the all-electron projector augmented-wave method (PAW), and then used to compute the insulating antiferromagnetic ground state of NiO and its optical properties. The electronic and optical properties have been investigated as a function of the Coulomb repulsion parameter U. We find that the value obtained from constrained LDA (U=8 eV) is not the best possible choice, whereas an intermediate value (U=5 eV) reproduces the experimental magnetic moment and optical properties satisfactorily. At intermediate U, the nature of the band gap is a mixture of charge transfer and Mott-Hubbard type, and becomes almost purely of the charge-transfer type at higher values of U. This is due to the enhancement of the oxygen 2p states near the top of the valence states with increasing U value.Comment: 23 pages, 6 figures, submitted to Phys. Rev.

Implementation of the LDA+U method using the full potential linearized augmented plane wave basis

We provide a straightforward and efficient procedure to combine LDA+U total energy functional with the full potential linearized augmented plane wave method. A detailed derivation of the LDA+U Kohn-Sham type equations is presented for the augmented plane wave basis set, and a simple ``second-variation'' based procedure for self-consistent LDA+U calculations is given. The method is applied to calculate electronic structure and magnetic properties of NiO and Gd. The magnetic moments and band eigenvalues obtained are in very good quantitative agreement with previous full potential LMTO calculations. We point out that LDA+U reduces the total d charge on Ni by 0.1 in NiO

Correlated metals and the LDA+U method

While LDA+U method is well established for strongly correlated materials with well localized orbitals, its application to weakly correlated metals is questionable. By extending the LDA Stoner approach onto LDA+U, we show that LDA+U enhances the Stoner factor, while reducing the density of states. Arguably the most important correlation effects in metals, fluctuation-induced mass renormalization and suppression of the Stoner factor, are missing from LDA+U. On the other hand, for {\it moderately} correlated metals LDA+U may be useful. With this in mind, we derive a new version of LDA+U that is consistent with the Hohenberg-Kohn theorem and can be formulated as a constrained density functional theory. We illustrate all of the above on concrete examples, including the controversial case of magnetism in FeAl.Comment: Substantial changes. In particular, examples of application of the proposed functional are adde

Optical studies of gap, hopping energies and the Anderson-Hubbard parameter in the zigzag-chain compound SrCuO2

We have investigated the electronic structure of the zigzag ladder (chain) compound SrCuO2 combining polarized optical absorption, reflection, photoreflectance and pseudo-dielectric function measurements with the model calculations. These measurements yield an energy gap of 1.42 eV (1.77 eV) at 300 K along (perpendicular) to the Cu-O chains. We have found that the lowest energy gap, the correlation gap, is temperature independent. The electronic structure of this oxide is calculated using both the local-spin-density-approximation with gradient correction method, and the tight-binding theory for the correlated electrons. The calculated density of electronic states for non-correlated and correlated electrons shows quasi-one-dimensional character. The correlation gap values of 1.42 eV (indirect transition) and 1.88 eV (direct transition) have been calculated with the electron hopping parameters t = 0.30 eV (along a chain), t_yz = 0.12 eV (between chains) and the Anderson-Hubbard repulsion on copper sites U= 2.0 eV. We concluded that SrCuO_2 belongs to the correlated-gap insulators.Comment: 24 pages, 8 figures, to be published in Phys.Rev.

Landscape, soil, lithology, climate and permafrost control on dissolved carbon, major and trace elements in the Ob River, Western Siberia

In order to foresee possible changes in the elementary composition of Arctic river waters, complex studies with extensive spatial coverage, including gradients in climate and landscape parameters, are needed. Here, we used the unique position of the Ob River, draining through the vast partially frozen peatlands of the western Siberia Lowland and encompassing a sizable gradient of climate, permafrost, vegetation, soils and Quaternary deposits, to assess a snap-shot (8–23 July 2016) concentration of all major and trace elements in the main stem (~3000 km transect from the Tom River confluence in the south to Salekhard in the north) and its 11 tributaries. During the studied period, corresponding to the end of the spring flood-summer baseflow, there was a systematic decrease, from the south to the north, of Dissolved Inorganic Carbon (DIC), Specific Conductivity, Ca and some labile trace elements (Mo, W and U). In contrast, Dissolved Organic Carbon (DOC), Fe, P, divalent metals (Mn, Ni, Cu, Co and Pb) and low mobile trace elements (Y, Nb, REEs, Ti, Zr, Hf and Th) sizably increased their concentration northward. The observed latitudinal pattern in element concentrations can be explained by progressive disconnection of groundwaters from the main river and its tributaries due to a northward increase in the permafrost coverage. A northward increase in bog versus forest coverage and an increase in DOC and Fe export enhanced the mobilization of insoluble, low mobile elements which were present in organo-ferric colloids (1 kDa—0.45 µm), as confirmed by an in-situ dialysis size fractionation procedure. The chemical composition of the sampled mainstream and tributaries demonstrated significant (p < 0.01) control of latitude of the sampling point; permafrost coverage; proportion of bogs, lakes and floodplain coverage and lacustrine and fluvio-glacial Quaternary deposits of the watershed. This impact was mostly pronounced on DOC, Fe, P, divalent metals (Mn, Co, Ni, Cu and Pb), Rb and low mobile lithogenic trace elements (Al, Ti, Cr, Y, Zr, Nb, REEs, Hf and Th). The pH and concentrations of soluble, highly mobile elements (DIC, SO4, Ca, Sr, Ba, Mo, Sb, W and U) positively correlated with the proportion of forest, loesses, eluvial, eolian, and fluvial Quaternary deposits on the watershed. Consistent with these correlations, a Principal Component Analysis demonstrated two main factors explaining the variability of major and trace element concentration in the Ob River main stem and tributaries. The DOC, Fe, divalent metals and trivalent and tetravalent trace elements were presumably controlled by a northward increase in permafrost, floodplain, bogs, lakes and lacustrine deposits on the watersheds. The DIC and labile alkaline-earth metals, oxyanions (Mo, Sb and W) and U were impacted by southward-dominating forest coverage, loesses and eluvial and fertile soils. Assuming that climate warming in the WSL will lead to a northward shift of the forest and permafrost boundaries, a “substituting space for time” approach predicts a future increase in the concentration of DIC and labile major and trace elements and a decrease of the transport of DOC and low soluble trace metals in the form of colloids in the main stem of the Ob River. Overall, seasonally-resolved transect studies of large riverine systems of western Siberia are needed to assess the hydrochemical response of this environmentally-important territory to on-going climate change

Annihilation of low energy antiprotons in silicon

The goal of the AE$\mathrm{\bar{g}}$IS experiment at the Antiproton Decelerator (AD) at CERN, is to measure directly the Earth's gravitational acceleration on antimatter. To achieve this goal, the AE$\mathrm{\bar{g}}$IS collaboration will produce a pulsed, cold (100 mK) antihydrogen beam with a velocity of a few 100 m/s and measure the magnitude of the vertical deflection of the beam from a straight path. The final position of the falling antihydrogen will be detected by a position sensitive detector. This detector will consist of an active silicon part, where the annihilations take place, followed by an emulsion part. Together, they allow to achieve 1$$ precision on the measurement of $\bar{g}$ with about 600 reconstructed and time tagged annihilations. We present here, to the best of our knowledge, the first direct measurement of antiproton annihilation in a segmented silicon sensor, the first step towards designing a position sensitive silicon detector for the AE$\mathrm{\bar{g}}$IS experiment. We also present a first comparison with Monte Carlo simulations (GEANT4) for antiproton energies below 5 MeVComment: 21 pages in total, 29 figures, 3 table