232 research outputs found
A high-temperature expansion method for calculating paramagnetic exchange interactions
The method for calculating the isotropic exchange interactions in the
paramagnetic phase is proposed. It is based on the mapping of the
high-temperature expansion of the spin-spin correlation function calculated for
the Heisenberg model onto Hubbard Hamiltonian one. The resulting expression for
the exchange interaction has a compact and transparent formulation. The quality
of the calculated exchange interactions is estimated by comparing the
eigenvalue spectra of the Heisenberg model and low-energy magnetic part of the
Hubbard model. By the example of quantum rings with different hopping setups we
analyze the contributions from the different part of the Hubbard model spectrum
to the resulting exchange interaction.Comment: 8 pages, 8 figure
Monte Carlo study of magnetic nanoparticles adsorbed on halloysite nanotubes
We study properties of magnetic nanoparticles adsorbed on the halloysite
surface. For that a distinct magnetic Hamiltonian with random distribution of
spins on a cylindrical surface was solved by using a nonequilibrium Monte Carlo
method. The parameters for our simulations: anisotropy constant, nanoparticle
size distribution, saturated magnetization and geometrical parameters of the
halloysite template were taken from recent experiments. We calculate the
hysteresis loops and temperature dependence of the zero field cooling (ZFC)
susceptibility, which maximum determines the blocking temperature. It is shown
that the dipole-dipole interaction between nanoparticles moderately increases
the blocking temperature and weakly increases the coercive force. The obtained
hysteresis loops (e.g., the value of the coercive force) for Ni nanoparticles
are in reasonable agreement with the experimental data. We also discuss the
sensitivity of the hysteresis loops and ZFC susceptibilities to the change of
anisotropy and dipole-dipole interaction, as well as the 3d-shell occupation of
the metallic nanoparticles; in particular we predict larger coercive force for
Fe, than for Ni nanoparticles.Comment: 10 pages, 12 figure
Bimeron nanoconfined design
We report on the stabilization of the topological bimeron excitations in
confined geometries. The Monte Carlo simulations for a ferromagnet with a
strong Dzyaloshinskii-Moriya interaction revealed the formation of a mixed
skyrmion-bimeron phase. The vacancy grid created in the spin lattice
drastically changes the picture of the topological excitations and allows one
to choose between the formation of a pure bimeron and skyrmion lattice. We
found that the rhombic plaquette provides a natural environment for
stabilization of the bimeron excitations. Such a rhombic geometry can protect
the topological state even in the absence of the magnetic field.Comment: 5 pages, 7 figure
Profile approach for recognition of three-dimensional magnetic structures
We propose an approach for low-dimensional visualisation and classification
of complex topological magnetic structures formed in magnetic materials. Within
the approach one converts a three-dimensional magnetic configuration to a
vector containing the only components of the spins that are parallel to the z
axis. The next crucial step is to sort the vector elements in ascending or
descending order. Having visualized profiles of the sorted spin vectors one can
distinguish configurations belonging to different phases even with the same
total magnetization. For instance, spin spiral and paramagnetic states with
zero total magnetic moment can be easily identified. Being combined with a
simplest neural network our profile approach provides a very accurate phase
classification for three-dimensional magnets characterized by complex
multispiral states even in the critical areas close to phases transitions. By
the example of the skyrmionic configurations we show that profile approach can
be used to separate the states belonging to the same phase
Mathematical modelling and analysis of the mushroom drying process at the optimal temperature
To preserve food is used drying method. It was found experimentally that drying mushroom caps and legs should
be conducted at temperatures close to 52,5°C and 55,5°C, accordingly. In this case, we can get the product of the
highest quality. Statistically, we proved that the drying processes of mushroom caps are different for fixed levels
of temperature (from 40° C to 80° C, by step 10° C). At the same time, at higher temperatures, the nature of the
process changes abruptly. Based on the experimental data, the polynomial regression model was built. This
model can used for estimating and forecasting a specific evaporation heat at the optimal temperature.To preserve food is used drying method. It was found experimentally that drying mushroom caps and legs should
be conducted at temperatures close to 52,5°C and 55,5°C, accordingly. In this case, we can get the product of the
highest quality. Statistically, we proved that the drying processes of mushroom caps are different for fixed levels
of temperature (from 40° C to 80° C, by step 10° C). At the same time, at higher temperatures, the nature of the
process changes abruptly. Based on the experimental data, the polynomial regression model was built. This
model can used for estimating and forecasting a specific evaporation heat at the optimal temperature
Double Counting in LDA+DMFT - The Example of NiO
An intrinsic issue of the LDA+DMFT approach is the so called double counting
of interaction terms. How to choose the double-counting potential in a manner
that is both physically sound and consistent is unknown. We have conducted an
extensive study of the charge transfer system NiO in the LDA+DMFT framework
using quantum Monte Carlo and exact diagonalization as impurity solvers. By
explicitly treating the double-counting correction as an adjustable parameter
we systematically investigated the effects of different choices for the double
counting on the spectral function. Different methods for fixing the double
counting can drive the result from Mott insulating to almost metallic. We
propose a reasonable scheme for the determination of double-counting
corrections for insulating systems.Comment: 7 pages, 6 figure
Аcute renal failure in patients with implanted LVAD in the early postoperative period
AKI is one of the major complications in the cardiac surgery group of patients in the world. In patients with LVAD in the short postoperative period, the situation with such a complication as AKI is associated with the state of hemodynamics and fluctuations in the parameters of the hemostasis system.
The purpose of this scientific work is to analyze the state of the blood coagulation system and its response to therapy and complications in the early postoperative period in fifty patients with implanted devices for mechanical support of the left ventricle, left ventricle assist device, LVAD, in the Silesian Heart Disease, Poland. Patients were divided into two groups, a control group receiving classical anticoagulation targeted therapy (ATT), which included the most controlled monotherapy with heparin, after reaching the target values of APTT, the addition and transition to monotherapy with warfarin until reaching the target INR and ASA, and the main, research group, who received an alternative ATT consisting of the previous one with the addition of P2Y12-receptor blockers and Xa-factors.
The results showed that the control group of patients with classical anticoagulant targeted therapy had greater mortality associated with AKI than the patients of the study group, and it was also demonstrated that the initially longer duration of surgery and intraoperative polyuria gave a greater percentage of AKI in the postoperative period.
The work was carried out within the framework of a bilateral agreement on scientific cooperation between the Department of Anesthesiology & Intensive Care at the National Medical Academy of Post-Graduate Education Named After P.L. Shupyk and the Silesian Center for Heart Diseases (Poland). This article is part of the analysis of the work on the analysis of the blood coagulation system in patients after implantation of the left ventricular mechanical circulatory support system with the analysis of such postoperative complication as acute kidney failure
Spatial inversion of gyrotropy parameter in conductivity tensor and charge transport peculiarities
Charge transfer is discussed for the case when gyrotropy parameter (Hall coefficient) varies along transport л-direction and inverses its sign. This situation takes place in contacts of the serially joined materials having electron and hole types of conductivity. Spatial inhomogeneity of conductivity and inversion of Hall coefficient sign are analyzed in terms of electric potential and current density distribution. It is shown that under inhomogeneous magnetic field the steady current skinning takes place in plate sample
Correlated band theory of spin and orbital contributions to Dzyaloshinskii-Moriya interactions
A new approach for calculations of Dzyaloshinskii-Moriya interactions in
molecules and crystals is proposed. It is based on the exact perturbation
expansion of total energy of weak ferromagnets in the canting angle with the
only assumption of local Hubbard-type interactions. This scheme leads to a
simple and transparent analytical expression for Dzyaloshinskii-Moriya vector
with a natural separation into spin and orbital contributions. The main problem
was transferred to calculations of effective tight-binding parameters in the
properly chosen basis including spin-orbit coupling. Test calculations for
LaCuO give the value of canting angle in a good agreement with
experimental data.Comment: 4 pages, 1 figur
Magnetostimulated inhomogeneity of electric field in aluminum
The results of low temperature experimental and theoretical study of potential distribution of stationary electric field in Al under the action of inhomogeneous magnetic field are presented
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