Vol 12, No 3 (2018)

Molecular relaxation in solid binary systems LiNO₃–LiClO₄, Na₂CO₃–Na₂SO₄, and KNO₃–KNO₂ was studied by Raman spectroscopy. The relaxation time of the ν₁(A) vibrations of the anion (NO₃⁻, CO₃²⁻) in the binary system was found to be smaller than in the individual crystal (nitrate or carbonate). The increase in the relaxation rate was explained by the presence of an additional relaxation mechanism of the vibrationally excited states of the anion in the binary system. This mechanism is associated with excitation of vibrations of another anion (ClO₄^-, SO₄^2-, NO₂^-) and generation of a lattice phonon. It was found that this relaxation mechanism takes place if the frequency difference of these vibrations corresponds to the region of sufficiently high density of states of the phonon spectrum.

The development of a new direction of research on the production and application of spin-polarized isotopes of noble gases, ³He and ¹²⁹Xe, is overviewed. Methods of laser hyperpolarization, problems of enhancing the efficiency of laser energy input, and methods of storing hyperpolarized (HP) isotopes are described. Examples and advantages of using HP isotopes in fundamental physics, engineering, medicine, and biology, as well as the progress in the creation of biosensors on hyperpolarized noble gases, are discussed. It has been shown that the study of protein structures and host–guest molecular complexes can prove useful in searching for means of the targeted delivery of radioactive isotopes (radiopharmaceuticals) in nuclear medicine. It is concluded that the progress in modern technologies for producing miniature electronic devices is suggestive of an imminent emergence of small-size scanners for human brain research. At the same time, a high sensitivity of the method is expected to provide the possibility of studying not only the structure of tissues and bloodstream, but also the response of the brain to various stimuli, and even cognitive functions.

The FTIR and FT-Raman spectra of tetrahydroxy-1,4quinone hydrate have been recorded in the regions 4000–400 and 3500–50 cm^–1 respectively. Using the observed Fourier-transform infrared spectroscopy (FTIR) and FT-Raman data, a complete vibrational assignment and analysis of the fundamental modes of the compound has been carried out. The optimum molecular geometry, harmonic vibrational frequencies, infrared intensities and Raman scattering activities, were calculated by the density functional theory (DFT/B3LYP) and Hartree–Fock (HF) method with 6-311+G(d,p) basis set. The difference between the observed and scaled wavenumber values of most of the fundamental vibrations is very small. A detailed interpretation of the infrared and Raman spectra of tetrahydroxy-1,4quinone hydrate is also reported. The calculated HOMO and LUMO energies show that charge transfer occurs within the molecule.

Migration of graphene fragments along the aluminum matrix in the solid phase was studied by molecular dynamics. The structure of the Al–C nanocomposite grain was studied by statistical geometry. The distributions of the topological and metric characteristics of truncated polyhedra were calculated for the Al subsystem; the distributions for the polyhedra constructed at the centers of mass of the hypothetical geometrical neighbors were calculated for the carbon subsystem. The graphene fragments are concentrated at the structural grain boundaries. The nanocomposite grains are preferably separated by single-layer graphene rather than by the two-layer graphene membrane.

The oxidation of Rizatriptan by diperiodatoargentate(III) has been studied by spectrophotometry at neutral pH. The kinetics of the reaction of Rizatriptan has been shown to principle of non-complementary oxidation steps. The initial step involves the deprotonated of the diperiodatoargentate(III) with the alkali; this rearranges during the displacement of a ligand to give free periodate and takes up another ligand monoperiodateargentate(III), combines with a substrate to endow with an intermediate complex which decomposes within a slow step to provide the final product in the following step with a first-order rate constant. The main product was identified by spot test, Fourier- transform infrared spectroscopy, Nuclear magnetic resonance and Liquid chromatography-mass spectrometry spectrum. A conceivable mechanism including pre equilibrium of adducts development between the complex and reductant was planned from the kinetics study. The rate conditions got from system can clarify all exploratory phenomena, and the activation parameters alongside rate constants of the rate determining step were ascertained.

It has been experimentally established that the chiroptical characteristics of freshly prepared solutions of trifluoroacetylated amino alcohols (TFAAAs) evolve before reaching equilibrium. The evolution can be monotone or quasi-oscillatory. The latter reflects the formation of successive levels of the hierarchy of chiral phases with an alternating sign of chirality in the solution. The fast (the characteristic time τ from ~30 s to ~30 min) and slow (τ ~ 1–3 h) stages of evolution have been experimentally revealed. It is shown via calculation that the fast stage corresponds to the early stages of the formation of the supramolecular structure of the solutions of TFAAAs, namely, the growth of strings with diameters from several nanometers to tenths of a micrometer, while the slow stage corresponds to the late stages in the formation of the structure of the solutions, namely, the growth of strings with diameters from tenths of a micrometer up to several micrometers.

Thermal reaction characteristics of nano/micron-sized aluminum mixtures in a carbon dioxide atmosphere were investigated by thermogravimetry that aimed to examine the interactions between nanosized aluminum powder and micron-sized aluminum powder. Thermal reaction characteristics of nano/micron-sized aluminum mixtures at different ratios were studied. The synergistic effect mechanism was discussed by comparing experiment result and theoretical calculation. The morphologies and compositions of products were obtained by scanning electron microscopy and X-ray diffraction technologies. Results indicated that there were three weight gain stages for nano/micron-sized aluminum mixtures at different ratios. Although the temperature range of synergistic effect of nano/micron-sized aluminum mixtures with various ratios had somewhat differences, there was a significant synergistic effect from about 900 to 1040°C. The products analyses indicated that the products morphologies of nano/micron-sized aluminum particles showed molten and stuck together, and products contained aluminum and α-Al₂O₃.

The applicability of the percolation theory to describe the combustion of powdered and pelletized Ti + C mixtures in the vicinity of the concentration limits of the combustion wave propagation using different methods of dilution with an inert material—fine and coarse Al₂O₃ particles—has been studied. It has been shown that the pelletized mixtures diluted with coarse inert particles by more than 50% undergo incomplete combustion; at the combustion limit, the incompleteness achieves 50%; this finding is in qualitative agreement with the percolation theory. It has been found that the obtained concentration limit of combustion (75 wt %) and the ratio of the combustion velocities of the undiluted mixture and the mixture at the propagation limit (2.6) correspond to the predictions of the percolation theory. The possibility of flame propagation at the calculated combustion temperature of the mixture below the melting point of titanium is attributed to the presence of a percolation cluster. Necessary conditions for the applicability of the percolation theory to describe the combustion processes in condensed gasless systems have been formulated.

The quantum dynamics of the propagation of the charge wave function in a uniform lattice containing a single impurity site is considered. A nonstationary problem is solved in the tight-binding approximation. The initial state is the wave function fully localized at one of the lattice sites. The coefficients of transmission of the wave packet through the impurity site and reflections from it are calculated as a function of the parameters of the problem, that is, the additional energy on the impurity and the distance between the impurity and the initial position of the charge. The problem is solved for two types of boundary conditions: an infinite and a semi-infinite lattice. Good agreement with numerical simulation is obtained.

Due to the gradual increase in genetic related disease worldwide, the synthesis, characterization and physicochemical investigation of medicinal compounds such as thiobarbiturates and their derivatives is a highly desired area of research. Keeping their importance as medicinal compounds in mind, herein we report the synthesis and physicochemical characterization of five selected thiobarbiturate samples namely (MKA20 MKA21, MKA22, MKA23, MKA24) by using various physicochemical techniques. All the selected thiobarbiturates and their derivatives were synthesized by the reaction of diethyl thiobarbituric acid with different aromatic aldehydes. The synthesized thiobarbiturates and their derivatives were analyzed by various electroanalytical techniques, which gave us valuable information about the nature of thiobarbiturates and their derivatives. Further, the preliminary interaction of these thiobarbiturate with Deoxyribonucleic acid in aqueous solution was also investigated by using Ultraviolet-Visible spectrometry. On the basis of various results obtained, it can be said that most of their properties and extent of interaction with Deoxyribonucleic acid are varying with changing the alkyl groups on one hand and the functional groups on the other hand.

Zn₂SnO₄ (ZTO) is a stable semiconductor in ZnO–SnO₂ system and important transparent conducting oxide (TCO) predominantly used in optoelectronic devices. ZTO thin films were prepared by RF magnetron sputtering using Zn₂SnO₄ ceramic target in this paper. The effects of annealing temperatures and oxygen contents on characterization of ZTO thin films were studied. The results show that ZTO thin films prepared by RF magnetron sputtering are amorphous with an optical band gap of 3.22 eV. After annealing at 650°C in Ar atmosphere for 40 min, ZTO films possess a spinel structure with an optical band gap of 3.62 eV. The atomic force microscope (AFM) data of morphology reveals that the surface roughness of films is about 2 nm. The results of energy dispersive spectrometer (EDS) show that the concentration ratio of Zn to Sn is in the range from 1.44 to 1.57. The results of Hall-effect-measurement system reveal that the resistivity of films varies from 102 to 10–1 Ωcm, carrier concentration is about 10¹⁷ cm^–3, and mobility ranges from 10⁰ to 10¹ cm² v^–1 s^–1.

A method for studying the Earth’s ionosphere at altitudes of the mesosphere and lower thermosphere based on creating artificial periodic irregularities in the ionospheric plasma by means of powerful radio waves is breafly described. Methods for determining the temperature and density of the neutral component and the velocity of vertical and turbulent motions by measuring the characteristics of the signal backscattered by the irregularities are described. The results of experiments performed on a SURA heating facility aimed at a comprehensive investigation of the natural processes occurring in the Earth’s lower ionosphere due to the propagation of atmospheric waves and turbulent phenomena are examined. Based on measurements of the amplitude and phase of the signal scattered by periodic irregularities, the most important characteristics of the neutral and plasma components of the Earth’s atmosphere at altitudes of the mesosphere and lower thermosphere are determined. Further research on the subject is discussed.

Plasma instability caused by an inhomogeneous energy density distribution is considered. It is shown that this instability can lead to the excitation of electrostatic ion-cyclotron and oblique ion-acoustic waves, generated in the presence of an inhomogeneous transverse electric field and a shear in the parallel drift velocity of the plasma particles. The considered physical mechanisms of the instability generation in plasma can serve as possible sources of broadband electrostatic turbulence in the auroral ionosphere.

Since 2013, the optical station of Maimaga (63° N, 129.5° E) has been continuously recording the OH(3,1) hydroxyl band with a spectrograph operating in the near-infrared region (~1.5 μm). In September 2015, a similar spectrograph was mounted at the polar geophysical observatory located in the Tiksi urban locality (71.6° N, 128.7° E). The present work compares the seasonal variation of the mesopause temperature measured at two different- latitude stations. In addition, preliminary comparisons are made for overnight variations for several nights. The comparison shows that there is a very good correlation between data obtained at the two stations, with a correlation coefficient of 0.83. A comparison with the predictions of the CIRA and MSIS empirical atmospheric models revealed a number of discrepancies.

The foundations of the quantum theory of distortion and delay of GPS satellite signal passing through D and E atmospheric layers are expound. The problem reduces to the resonant scattering of photons moving in the electromagnetic field of the signal on Rydberg complexes populated in a two-temperature nonequilibrium plasma. The processes of creation of additional photons as a result of stimulated emission and resonance scattering of photons are considered. In the present work, the quantum theory of the propagation of a satellite signal in the upper atmosphere of the Earth was proposed for the first time. The general questions of the theory and possible consequences are discussed. It is shown that the processes occurring here are directly related to the resonant quantum properties of the medium propagation. The first process leads to a direct increase in the power of the received signal, and the second to a shift in the signal carrier frequency and the time delay of its propagation. This occurs because of the scattering of the Rydberg electron by the ion core and the neutral medium molecule in the intermediate autoionization states of the composite system populated by the strong non-adiabatic coupling of electron and nuclear motions. Determination of the relationship between the frequency shift Δν and delay time Δτ of a satellite signal with quantum dynamics inside the Rydberg complex А**М is the general purpose of this paper.

A comparative analysis of total electron content (TEC) fluctuations and auroral activity, which characterizes the polar ionosphere during periods of substorm activity, is performed. The analysis is based on GPS/GLONASS observations at auroral and subauroral stations and data on auroral emissions obtained at the Yakutsk subauroral station and the Poker Flat (Alaska) auroral station. A detailed analysis is carried out for the storm on January 7, 2015. During this event, a sharp increase in the auroral activity and in TEC fluctuations from 09 to 13 UT was observed. A similarity of the dynamics of the auroral oval and the space–time distribution of TEC fluctuations associated with ionospheric irregularities in the oval is demonstrated. There is a close correlation between the positions of the auroral oval and the irregularity oval. The positions of the auroral oval, predicted by the NORUSKA Russian–Norwegian model, and of the TEC irregularity oval are compared. In general, the positions of the ovals are close to each other. The existing discrepancy may be due to the fact that the auroral oval is projected to an altitude of 110 km, whereas the irregularity oval, to an altitude of 450 km, and that the curvature of the magnetic force lines is not taken into account. The influence of auroral disturbances on navigational measurements manifests itself through the fact that, during disturbances, faults and failures in the operation of navigation equipment at auroral and subauroral stations increase.

A semiempirical model of ionospheric conductivity for calculating the coefficients of ionic friction and magnetic twisting is described. The influence of diurnal variations of the ionic friction and magnetic twisting in the upper atmosphere on the formation of latitudinal and altitudinal structures of various components of atmospheric tides is considered. It is shown that taking into account diurnal variations of the ionic friction and magnetic twisting leads to an additional generation of non-migrating tides in the thermosphere due to the nonlinear interaction of migrating tides with these variations.

The mechanism of a chemical reaction in an ideal mixing reactor has been found. It was described by two ordinary differential equations within the framework of the law of mass action and reproduces sustained chaotic oscillations. The randomness of oscillations was confirmed by the numerical calculations of the kinetic model and Lyapunov exponents.