Proximity effect in atomic-scaled hybrid superconductor/ferromagnet structures: crucial role of electron spectra

We study the influence of the configuration of the majority and minority spin subbands of electron spectra on the properties of atomic-scaled superconductor-ferromagnet S-F-S and F-S-F hybrid structures. At low temperatures, the S/F/S junction is either a 0 or junction depending on the energy shift between S and F materials and the anisotropy of the Fermi surfaces. We found that the spin switch effect in F/S/F system can be reversed if the minority spin electron spectra in F metal is of the hole-like type

Critical Current Oscillations in Strong Ferromagnetic Pi-Junctions

We report magnetic and electrical measurements of Nb Josephson junctions with strongly ferromagnetic barriers of Co, Ni and Ni80Fe20 (Py). All these materials show multiple oscillations of critical current with barrier thickness implying repeated 0-pi phase-transitions in the superconducting order parameter. We show in particular that the Co barrier devices can be accurately modelled using existing clean limit theories and so that, despite the high exchange energy (309 meV), the large IcRN value in the pi-state means Co barriers are ideally suited to the practical development of superconducting pi-shift devices.Comment: 4 pages 3 figures 1 table. Revised version as accepted for publication. To appear in Physical Review Letter

СИСТЕМНАЯ ОЦЕНКА НАУЧНО-МЕТОДЧЕСКИХ МАТЕРИАЛОВ ПО ЭКОНОМИЧЕСКОМУ РЕГУЛИРОВАНИЮ ПРОДОВОЛЬСТВЕННОЙ БЕЗОПАСНОСТИ

One of the priority aims of the world community is food security. Analysis of global problems shows the long-term persistence of shortage in agricultural raw materials and food, exacerbated by unfavorable situation in the world market, the impact of globalization, political, social, economic and military crises. Reserves for increasing agricultural production are limited, and further intensification leads to decrease in quality and threats environmental safety. It becomes increasingly difficult for the agrarian food systems of countries and regions to provide population with sufficient quantities of safe and nutrition valuable food products, which is the reason for the large amount of various forms of malnutrition. The article presents assessment of research and methodological materials of economic regulation of food security. The most important for the practice of Belarus mechanisms, forms and tools for ensuring food security, used in developed countries are established. Classification of criteria and indicators of food security has been performed by a number of traits: the unity of definition, the simplicity of calculation, availability of the initial information in official statistics, etc. The main criteria have been highlighted, as well additional indicators have been formulated. A model of food safety regulation is developed based on comprehensive assessment of five spheres of management: the sphere of production of initial agricultural products; the sphere of production of finished food; the sphere of state management of agro-food complex; the sphere of material and technical (resource) support of agro-industrial complex; the sphere of market products turnover and consumption. The following measures for sustainable food security are identified as key measures: implementation of research and technological progress achievements, transfer of innovations and development of the national agrarian science.Одной из приоритетных задач мирового сообщества является защищенность в продовольственной сфере. Анализ глобальных проблем свидетельствует о сохранении в долгосрочной перспективе дефицита ресурсов сельскохозяйственного сырья и продовольствия, который усугубляется неблагоприятной конъюнктурой мирового рынка, влиянием процессов глобализации, политических, социальных, экономических и военных кризисов. Резервы наращивания сельскохозяйственного производства ограничены, а дальнейшая интенсификация ведет к снижению качества и угрозам экологической безопасности. Агропродовольственным системам стран и регионов становится все сложнее обеспечивать население достаточными по количеству, безопасными и богатыми питательными веществами пищевыми продуктами, что является причиной масштабного проявления различных форм неполноценного питания. В статье представлена оценка научно-методических материалов по экономическому регулированию продовольственной безопасности. Выявлены наиболее значимые для практики Беларуси механизмы, формы и инструменты обеспечения продовольственной безопасности, применяемые в развитых странах. Выполнена классификация критериев и показателей продовольственной безопасности по ряду признаков: единство определения, простота расчета, наличие в официальной статистике исходной информации и др. Выделены основные критерии, а также сформулированы дополнительные показатели. Разработана модель регулирования продовольственной безопасности, основанная на комплексной оценки пяти сфер хозяйствования и управления: сфера производства исходной сельскохозяйственной продукции; сфера производства готового продовольствия; сфера государственного управления агропродовольственным комплексом; сфера материально-технического (ресурсного) обеспечения АПК; сфера рыночного товарооборота и потребления. В качестве ключевых мер по устойчивому обеспечению продовольственной безопасности выделены: внедрение достижений научно-технического прогресса, трансфер инноваций, развитие национальной аграрной науки.

Scattering by magnetic and spin-orbit impurities and the Josephson current in superconductor-ferromagnet-superconductor junctions

We analyze the Josephson current in a junction consisting of two superconductors (S) and a ferromagnetic layer (F) for arbitrary impurity concentration. In addition to non-magnetic impurities, we consider also magnetic ones and spin-orbit scattering. In the limit of weak proximity effect we solve the linearized Eilenberger equation and derive an analytical expression for the Josephson critical current valid in a broad range of parameters. This expression enables us to obtain not only known results in the dirty and clean limits but also in a intermediate region of the impurity concentration, which may be very important for comparison with experimental data.Comment: revised versio

Evolution of the local superconducting density of states in ErRh4_4B4_{4} close to the ferromagnetic transition

We present local tunneling spectroscopy experiments in the superconducting and ferromagnetic phases of the reentrant superconductor ErRh$_4$B$_{4}$. The tunneling conductance curves jump from showing normal to superconducting features within a few mK close to the ferromagnetic transition temperature, with a clear hysteretic behavior. Within the ferromagnetic phase, we do not detect any superconducting correlations. Within the superconducting phase we find a peculiar V-shaped density of states at low energies, which is produced by the magnetically modulated phase that coexists with superconductivity just before ferromagnetism sets in.Comment: 5 pages, 4 figure

The role of SH groups in the regulation of Gardos channels in glucose deficiency

Background. Disruption of the energy balance of erythrocytes under conditions of a decrease in the glycolysis level can cause a change in the ion permeability of their membrane.   The aim. To study Ca2+-dependent potassium permeability of the erythrocytes membrane in the presence of SH group modifiers under conditions of glucose deficiency.   Materials and methods. The study used precipitated erythrocytes obtained from the blood of 20 male Wistar rats. The change in the Ca2+-dependent potassium conductivity of the erythrocyte membrane was determined using the potentiometric method. The A23187-and redox-induced hyperpolarization responses of erythrocytes were evaluated.   Results. Glucose deficiency in the medium, as well as the use of the glycolysis inhibitor 2-deoxyglucose, led to an increase in the amplitude of A23187-stimulated membrane hyperpolarization by the opening of the Gardos channels. At the same time, the redox-dependent hyperpolarization of the erythrocyte membrane turned out to be insensitive to a decrease in the glucose content in the medium and to the glycolysis inhibition. The effects of SH group modifiers in the normal incubation medium and under glucose deficiency turned out to be multidirectional and depended on the method of stimulation of Gardos channels.   Conclusion. The results obtained indicate that metabolic disorders in erythrocytes under conditions of glucose deficiency lead to a change in the mechanisms of control of Gardos channels with the participation of SH groups of the proteins of these channels or their regulatory proteins

Superconducting decay length in a ferromagnetic metal

The complex decay length xi characterizing penetration of superconducting correlations into a ferromagnet due to the proximity effect is studied theoretically in the frame of the linearized Eilenberger equations. The real part xi_1 and imaginary part xi_2 of the decay length are calculated as functions of exchange energy and the rates of ordinary, spin flip and spin orbit electronic scattering in a ferromagnet. The lengths xi_1,2 determine the spatial scales of, respectively, decay and oscillation of a critical current in SFS Josephson junctions in the limit of large distance between superconducting electrodes. The developed theory provides the criteria of applicability of the expressions for xi_1 and xi_2 in the dirty and the clean limits which are commonly used in the analysis of SF hybrid structures.Comment: 5 pages, 3 figure

MRI of the arterial wall in resistant hypertension associated with type 2 diabetes mellitus

BACKGROUND: Damage of arterial walls in diabetes mellitus associated with arterial hypertension is major factor delivering lesion of target organs. Currently, enough data is not available about imaging and quantitative evaluations of arterial wall. There is no enough data available about the relations between MRI and inflammatory and metabolic markers in patients with resistant arterial hypertension concomitant with diabetes mellitus. AIMS: Quantitative assessment of the intensity of paramagnetic contrast enhancement of the arterial wall, in particular renal arteries walls, in relation with inflammatory and metabolic markers in patients with resistant arterial hypertension concomitant with diabetes mellitus. MATERIALS AND METHODS: The study groups were comprised of 28 patients (ageing 60,7±6,5 years) with resistant hypertension accompanied with diabetes mellitus and 17 patients (aging 57,7±5,0 years) with resistant hypertension without diabetes mellitus. The average systolic/diastolic pressure obtained from a 24-h monitor study was as high as 156,8±16,9/81,9,0±13,5 mm Hg in the group with diabetes and 154,8±11,9/88,5±10,4 mm Hg in the group without diabetes. The values of glycaemia, the level of glycated haemoglobin, and C-reactive protein were determined. The MRI studies were carried out using 1,5 Т MRI Toshiba Vantage Titan scanner. After that, the intravenous contrast enhancement has been carried out (with 0,5 М paramagnetic, as 0,2 ml/Kg). The index of enhancement (IE) was then calculated from these data, as a ratio of intensities of contrast-enhanced image to the initial nonenhanced MRI scan. RESULTS: The correlation was obtained for IE of arterial wall and data of blood pressure. Increased IE was correlated with ageing and hemodynamic factors. Also the correlation was observed for IE proximal, medium and distal parts of renal arteries and values of glycaemia and NOMA-index were obtained. Negatively correlated values for IE and adiponectin in the group with diabetes mellitus were obtained. The association between IE and C-reactive protein remained significant in the group without diabetes mellitus. CONCLUSIONS: MRI with contrast enhancement of arterial walls allows evaluating the anatomy of renal arteries and allows quantifying the pathophysiologic factors of their walls in patients with resistant hypertension accompanied with diabetes mellitus. MRI characteristics of the arterial wall were associated not only with hemodynamic and metabolic data, but also with markers of inflammation

Temperature dependence of the emission linewidth in MgO-based spin torque nano-oscillators

Spin transfer driven excitations in magnetic nanostructures are characterized by a relatively large microwave emission linewidth (10 -100 MHz). Here we investigate the role of thermal fluctuations as well as of the non-linear amplitude-phase coupling parameter and the amplitude relaxation rate to explain the linewidth broadening of in-plane precession modes induced in planar nanostructures. Experiments on the linewidth broadening performed on MgO based magnetic tunnel junctions are compared to the linewidth obtained from macrospin simulations and from evaluation of the phase variance. In all cases we find that the linewidth varies linearly with temperature when the amplitude relaxation rate is of the same order as the linewidth and when the amplitude-phase coupling parameter is relatively small. The small amplitude-phase coupling parameter means that the linewidth is dominated by direct phase fluctuations and not by amplitude fluctuations, explaining thus its linear dependence as a function of temperature

On the Theory of Directional Solidification in the Presence of a Mushy Zone

Abstract: A model is developed for the directional solidification of a binary melt with a two-phase zone (mushy zone), where the fraction of the liquid phase is described by a space–time scaling relation. Self-similar variables are introduced and the interphase boundary growth is inversely proportional to the square root of time. The mathematical model of the process is reformulated using self-similar variables. Exact self-similar solutions of heat-and-mass transfer equations are determined in the presence of two mobile phase-transition boundaries, namely, solid–mushy zone and mushy zone–liquid ones. The temperature and impurity concentration distributions in the solid phase, the mushy zone, and the melt are found as integral expressions. A decrease in the dimensionless cooled-boundary temperature leads to an increase in the solidification rate and the fraction of the liquid phase. The solidification rate, the parabolic growth constants, and the fraction of the liquid phase at the solid–mushy zone boundary are determined depending on the scaling parameter and the thermophysical constants of the solidifying melt. The positions of the solid–mushy zone and mushy zone–binary melt phase transition boundaries are found. The dependences of the solidification rate (inversely proportional to the square root of time) are analyzed. The scaling parameter significantly is shown to substantially affect the solidification rate and the fraction of the liquid phase in the phase transformation region. The developed model and the method of its solution can be generalized to the case of directional solidification of multicomponent melts in the presence of several phase transformation regions (e.g., main and cotectic two-phase zones during the solidification of three-component melts). © 2021, Pleiades Publishing, Ltd.This work was supported by the Russian Foundation for Basic Research (project no. 18-58-00034 Bel_a) and the Belarussian Foundation for Basic Research (project no. F18R-195)