Using synchrotron radiation X-ray fluorescence analysis in a chemotaxonomic study of some Siberian species of the genus Pentaphylloides hill

The elemental composition of four species of the genus Pentaphylloides Hill is determined by means of synchrotron radiation X-ray fluorescence analysis (SRXRF). Each of the studied species is characterized by specific concentrations of elements that are typical of it and can be used in a comparative analysis of other species and be included in a corresponding database. In the case of P. fruticosa and P. x mandshurica, a high content of microelements is observed in all organs that distinguishes them from other species.     

Bulk viscosity of quark-gluon matter in a magnetic field

On the basis of low-energy QCD theorems, the bulk viscosity ζ(T, µ, H) is expressed in terms of basic thermodynamic quantities that characterizes quark-gluon matter at finite temperature and a finite baryon density in a magnetic field. Various limiting cases are considered.     

Quartet states of the lepton sector

A holistic study of the lepton sector is fulfilled in the framework of rigorous restrictions by five input suppositions. All leptons are divided into three classes on the structure of their equations. They are singlets, doublets and quartets. The quartet states are the most interesting among them from the point of view of their properties and possible physical interpretations.     

Specific features of the crystal structure and magnetic properties of the DyFeTi2O7 compound

Results of studying the specific features of formation of the crystal structure and distribution of iron cations over the sites in the DyFeTi₂O₇ compound have been presented and the comparison with the GdGaTi₂O₇ isostructural compound has been performed. The atomic disorder in the distribution of the Fe³⁺ ions over structural sites in the DyFeTi₂O₇ compound is confirmed by the Mössbauer spectroscopy and X-ray diffractometry. The results of magnetic measurements in the low-temperature region have revealed an inflection point in the temperature dependence of the magnetic moment and its dependence on the magnetic prehistory of the sample. The obtained experimental data suggest that there is a spin glass state with freezing point T _f = 6 K in the DyFeTi₂O₇ compound.     

Computer simulation of the structure and raman spectra of GaAs polytypes

The structure, energy of formation, and Raman spectra of several polytypes (3C, 2H, 4H, and 8H) of gallium arsenide GaAs have been investigated using quantum mechanical calculations based on the local density functional theory. It has been found that the energy of the formation of hexagonal polytypes increases with an increase in the length of the periodicity and approaches the value corresponding to the ground state, i.e., to the structure of the 3C polytype. It has been shown that the calculated frequencies of normal vibrations of different polytypes are consistent, with good accuracy (±6 cm^?1), with the scheme of folding of the phonon branches. In the calculated Raman spectra of the polytypes, there are new lines (forbidden in the spectrum of the 3C polytype) which can serve as characteristic lines of other polytypes. Similar lines can be found in the Raman spectra of GaAs nanowhiskers. This result has opened up new prospects for the application of Raman spectroscopy to the characterization of the structure of these nano-objects.     

On the problem of the LO-TO splitting of the soft mode in CaTiO3

The dispersion analysis of the panorama reflection spectrum of ceramic calcium titanate has been performed following the additive and factorized dispersion models with the goal to reveal the degree of adequacy of each of these models for determining the dispersion parameters of phonon modes. The correspondence of longitudinal and transverse IR-active vibrations has been established for the cubic and orthorhombic phases. Giant LO-TO splitting of the low-frequency soft mode (700 cm^?1), which leads to the inversion of the frequencies of all other IR vibrations in this region, has been found. This result is in good agreement with first-principles calculations.     

Dynamic loading of solids with a negative slope of the melting curve

The results of experiments on shock-wave loading of materials distinguished by a negative slope of the melting curve are reported. An anomalous situation is possible, when the material is melted by a shock wave and then a fast transition to the solid phase takes place in the expansion wave. The newly formed phase should be a nanostructural formation of the given element. Experiments confirmed the existence of the transition from the liquid to the solid phase of the nanostructural modification.