Локально-катастрофические сукцессии лесной растительности в зонах расширения шахтных полей Западного Донбасса

The forest herbaceous vegetation communities in the zone of mine fields have been investigated. A seral dynamics of phytocenosis is characterised on the basis of bioindication of changes in the plant associations’ structure on disturbed lands.Досліджено угруповання лісової трав’янистої рослинності в зоні поширення шахтних полів. Охарактеризовано сукцесійну динаміку фітоценозу на основі біоіндикації змін структури рослинних угруповань на порушених землях.Досліджено угруповання лісової трав’янистої рослинності в зоні поширення шахтних полів. Охарактеризовано сукцесійну динаміку фітоценозу на основі біоіндикації змін структури рослинних угруповань на порушених земля

X-ray Diffraction Study of the NaF – LiF – LnF3 (Ln=La,Nd) Eutectic Composition in the Liquid and Solid States

The ternary eutectic alloy with the composition 33 mol % NaF+53 mol % LiF+14 mol % NdF3 has been studied in the liquid and solid states using differential thermal analysis and X-ray diffraction at room and high temperatures. The obtained results demonstrate that the eutectic alloy undergoes no phase transformations at temperatures from 298 K to melting point. Analysis of RMC models of the melt indicates that there is no dense non-crystalline packing of the fluorine anions in contrast to the eutectic NaF—LiF—LaF3 melt

Optimal electron, phonon, and magnetic characteristics for low energy thermally induced magnetization switching

Using large-scale computer simulations, we thoroughly study the minimum energy required to thermally induced magnetization switching (TIMS) after the application of a femtosecond heat pulse in transition metal-rare earth ferrimagnetic alloys. We find that for an energy efficient TIMS, a low ferrimagnetic net magnetization with a strong temperature dependence is the relevant factor for the magnetic system. For the lattice and electron systems, the key physics for efficient TIMS is a large electron-phonon relaxation time. Importantly, we show that as the cooling time of the heated electrons is increased, the minimum power required to produce TIMS can be reduced by an order of magnitude. Our results show the way to low power TIMS by appropriate engineering of magnetic heterostructures

Unified decoupling scheme for exchange and anisotropy contributions and temperature-dependent spectral properties of anisotropic spin systems

We compute the temperature-dependent spin-wave spectrum and the magnetization for a spin system using the unified decoupling procedure for the high-order Green's functions for the exchange coupling and anisotropy, both in the classical and quantum case. Our approach allows us to establish a clear crossover between quantum-mechanical and classical methods by developing the classical analog of the quantum Green's function technique. The results are compared with the classical spectral density method and numerical modeling based on the stochastic Landau-Lifshitz equation and the Monte Carlo technique. As far as the critical temperature is concerned, there is a full agreement between the classical Green's functions technique and the classical spectral density method. However, the former method turns out to be more straightforward and more convenient than the latter because it avoids any \emph{a priori} assumptions about the system's spectral density. The temperature-dependent exchange stiffness as a function of magnetization is investigated within different approaches

Temperature-dependent exchange stiffness and domain wall width in Co

The micromagnetic exchange stiffness is a critical parameter in numerical modeling of magnetization dynamics and reversal processes, yet the current literature reports a wide range of values even for such simple and widely used material as cobalt. Using the ab initio estimated Heisenberg parameters we calculate the low temperature micromagnetic exchange stiffness for hexagonal-close-packed (hcp) and face-centered-cubic cobalt. For hcp Co they are slightly different in the directions parallel and perpendicular to the c axis. We establish the exchange stiffness scaling relation with magnetization A(m)∼m1.8 valid for a wide range of temperatures. For hcp Co we find an anisotropic domain wall width in the range 24-29 nm which increases with temperature. The results form a critical input for large-scale temperature-dependent micromagnetics simulations and demonstrate the importance of correct parametrization for accurate simulation of magnetization dynamics

Domain wall damped harmonic oscillations induced by curvature gradients in elliptical magnetic nanowires

Understanding the domain wall (DW) dynamics in magnetic nanowires (NW) is crucial for spintronic-based applications demanding the use of DWs as information carriers. This work focuses on the dynamics of a DW displacing along a bent NW with an elliptical shape under the action of spin-polarized electric currents and external magnetic fields. Our results evidence that a curvature gradient induces an exchange-driven effective tangential field responsible for pinning a DW near the maximum curvature point in a NW. The DW equilibrium position depends on the competition between the torques produced by the external stimuli and the curvature-induced effective fields. When the external stimuli are below a certain threshold, the DW follows a damped harmonic oscillation around the equilibrium position. Above this threshold, DW displaces along the NW under an oscillatory translational motion

Thermal Plasma of Electric Arc Discharge Between Cu-Cr Composite Electrodes

This work deals with investigations of model plasma source realised as electric arc discharge in gas atmosphere between Cu-Cr composite electrodes. Radial distributions of temperature and electron density in arc plasma column were studied by optical emission spectroscopy. The content of electrode metals' vapours in discharge was calculated on the base of experimentally obtained plasma parameters as initial data. So, in this way the erosion properties of such composition can be determined

Investigation of thermal plasma of arc discharge between novel composite Cu-W materials

In this work, the plasma emission of electric arc discharges between pairs of composite Cu-W electrodes was investigated by optical emission spectroscopy. Electrodes manufactured of Cu-W 50 vol.% composite materials by shock sintering technology at temperatures of 750, 850, 950, and 1050°C were used. The radial distributions of plasma temperature were determined by Boltzmann plot technique on the basis of the absolute values of intensity of both copper and tungsten spectral lines. The concentration of metal atoms of electrode origin (copper and tungsten) in the positive plasma column of electric arc discharges between studied electrodes manufactured of composite Cu-W materials was determined by the method of absolute intensities. The intensity of erosion of individual components of composite materials is estimated in an indirect way by comparing the radial distributions of atoms of materials of electrode origin for each type of the investigated arc discharge.Методами оптичної емісійної спектроскопії досліджено випромінювання плазми електродугових розрядів між парами композитних Cu-W-електродів. Використано електроди, виготовлені з композитних матеріалів Cu-W 50 об.% за технологією ударного спікання при температурах 750, 850, 950 і 1050°C. Методом діаграм Больцмана із залученням абсолютних значень інтенсивності спектральних ліній як міді, так і вольфраму, визначено радіальні розподіли температури плазми електродугових розрядів. Методом абсолютних інтенсивностей визначено концентрацію атомів металів електродного походження (міді та вольфраму) в позитивному стовпі плазми електродугових розрядів між досліджуваними електродами з композитних матеріалів Cu-W. Інтенсивність ерозії окремих складових композитних матеріалів оцінена в непрямий спосіб із порівняння радіальних розподілів атомів матеріалів електродного походження для кожного типу досліджуваного дугового розряду