Samples of natural and synthetic tochilinites and valleriites were investigated by Mössbauer spectroscopy. Synthesis of tochilinite was carried out at different temperatures and Fe/Mg ratio in the initial mixture. The relative amounts of obtained phases as functions of Mg atom relative content in the initial mixture were derived. It was shown that Mg atoms preferred to occupy one of two nonequivalent positions in brucite-like layers when entering the tochilinite structure. Parameters of hyperfine interaction were determined for valleriite and crystal chemical identification of 57Fe subspectra was carried out.
Aluminium-based rapidly quenched alloys of nominal composition of Al90Fe7Nb3 and Al94Fe2V4 were studied by Mössbauer spectroscopy. Samples annealed up to 573K showed amorphous structure represented by quadrupole-split doublets. From the corrected spectra areas, the values of f-factor and Debye temperature were calculated for both samples in the as-cast state. In the case of AlFeNb sample, f-factor was estimated to be f = 0.26 and for AlFeV, f = 0.31. High-temperature annealing at 773K and 873K induced a formation of nano-and microcrystalline structures. Mössbauer spectra of both compositions (with vanadium as well as with niobium) annealed at 773K showed superposition of crystalline phases with dominant contribution of Al3Fe alloy. During annealing at 873K, phases with large grains and a small amount of the FeAl metastable phase were developed.
Modification of silicon single crystal surface by the action of nitrogen quasistationary compression plasma flow (CPF) generated by magnetoplasma compressor is studied. It was found that during single pulse surface treatment regular fracture features are obtained on the Si (111) and Si (100) surface in the target central part. Some of these regular structures can become free from the underlying bulk, formed as blocks ejected from the surface. Also, oriented silicon periodic structures are produced in the target periphery part. These surface phenomena are results of specific conditions during CPF interaction with silicon surface. High plasma flow energy density, large dynamic pressure, thermodynamic parameters gradients and induced magnetic field on treated surface cause rapid heating and melting of surface layer, as well as surface fracturing, long existence of molten layer and fast cooling and recrystalisation.
Longitudinal optical phonons have been used to interpret the electronic energy relaxation in quantum dots and at the same time they served as a reservoir, with which the electronic subsystem is in contact. Such a phonon subsystem is expected to be passive, namely, in a long-time limit the whole system should be able to achieve such a stationary state, in which statistical distributions of both subsystems do not change in time. We pay attention to this property of the LO phonon bath. We show the passivity property of the so far used approximations to electronic transport in quantum dots. Also we show a way how to improve the passivity of LO phonon bath using canonical Lang-Firsov transformation.
The advection of a passive scalar quantity by incompressible helical turbulent flow has been investigated in the frame of an extended Kraichnan model. Statistical fluctuations of the velocity field are assumed to have the Gaussian distribution with zero mean and defined noise with finite time-correlation. Actual calculations have been done up to two-loop approximation in the frame of the field-theoretic renormalization group approach. It turned out that the space parity violation (helicity) of a stochastic environment does not affect anomalous scaling which is the peculiar attribute of corresponding model without helicity. However, stability of asymptotic regimes, where anomalous scaling takes place, and the effective diffusivity strongly depend on the amount of helicity.
