Vol 62, No 3 (2017)

The instant coffee model has been taken to study self-sustained oscillations in liquid dispersive media using dynamic self-organization processes in drying droplets that stay sessile on a solid wetted substrate. The width of the formed ring and the dynamics of mechanical properties of the drying sediment and the way they fluctuated over 11 h of the experiment have been measured. Analysis has shown a high degree of correlation between these indicators. This dynamics reflects processes that develop in the examined liquid medium. The possible mechanism of self-sustained oscillations, which is related to the aggregation–disaggregation of the colloidal phase and fluctuations of the interphase tension, has been discussed. The practical significance of this work is that fluctuation processes in liquid dispersive media need to be taken into account as a natural source of systematic measurement error.

The methodology and results of mass-spectrometric studies of producing positive ions as a result of the dissociative ionization of a molecular selenium beam by electron impact are discussed. The appearance energies of fragment ions were determined from the ionization efficiency curves. The dynamics of production of molecular selenium ions in the temperature range of 420–500 K was also examined. The energy dependences of efficiency of production of singly charged Se_n⁺ ions for n = 1–4 and the doubly charged selenium ion in the interval from the threshold to 36 eV were studied for the first time. The observed specific features of effective ionization cross sections were analyzed.

The ratio of amplitudes of waves generated by different interfaces in stratified inhomogeneous liquid is analytically studied. The amplitudes of waves generated by the second interface depend on the initial conditions and can be greater or less than the amplitudes of waves generated by the third interface. The amplitude ratio of the external and internal waves significantly depends on the ratio of liquid densities and layer thicknesses. Substantial effect of the initial conditions is manifested as a variation in the ratio of the amplitudes of external and internal waves and the amplitude ratio of waves generated by different interfaces.

For hydrogen ions source based on reflective discharge with hollow cathode the investigations of the effect of discharge current and gas pressure on the component composition of the ion beam have been performed. It has been shown that the optimization of the discharge parameters makes it possible to achieve up to 70% triatomic hydrogen ions H₃⁺ in the beam.

Quantum chemistry calculations of the intracrystalline potential relief in the nanolattice of LaF₃ superionic crystal that contains 1200 ions and measures 3.5 × 2.0 × 2.2 nm along the x, y, and z axis, respectively, have been performed. Using the MOPAC 2012 program package, the potential relief profile has been simulated in the central part of the nanolattice for an elementary act of disordering in the lowest melting sublattice of F₁ ions. It has been found that the height E_m of barriers that prevent the motion of F₁ in the dielectric phase of LaF₃ crystal equals 0.37 eV and decreases to 0.15 eV in the superionic state. In addition, activation energy E_a of F₁ sublattice disordering in the dielectric and superionic states is equal to 0.16 and 0.04 eV, respectively. The profiles of the potential relief calculated on the xy and xz faces of the LaF₃ 3D nanolattice for the case when an F₁ ion moves along the x crystal axis in the dielectric state are presented. The corresponding energy barriers are 1.5–2.0 times lower than those at the center of the LaF₃ nanlattice.

We have studied the regularities in the evolution of macroscopic nonuniformities in the plastic flow of metals in the form of the Chernov–Lüders bands and the Portevin—Le Chatelier effect. The regularities in the evolution of strain inhomogeneity in these two cases have been established, and the kinetics of motion of the Chernov–Lüders fronts and abrupt deformation in the Portevin–Le Chatelier effect has been analyzed. It has been shown that the Chernov–Lüders fronts and Portevin–Le Chatelier jumpwise straining can be treated as macroscopic autowave processes of switching and excitation, respectively, in deformed media of various origins.

Electret properties and structural peculiarities have been studied for fine-dispersed heterogeneous systems using the example of mechanoactivated natural-coal grains immersed into a polar aqueous matrix. The observed accumulation of currents with no external voltage applied indicates the formation of a potential difference of an internal electric field in test objects. It has been shown that an aqueous-phase layer with rigid fixation of water molecules is formed at the interfaces. The layer is capable of acquiring functions of a potential barrier that hampers transitions of both free water molecules and water molecules oriented by the system’s internal electric field.

The crystallization conditions and Raman spectra of LiNbO₃ : Zn crystals (0.02–8.91 mol % ZnO in the melt) have been investigated. It has been established that the most favorable conditions for growing optically and compositionally homogeneous heavily doped LiNbO₃ : Zn crystals, which are characterized by a low photorefractive effect, are implemented in the ZnO concentration range of ~4.0–6.76 mol % in the melt. Since the distribution coefficient K_eff decreases significantly with an increase in the ZnO concentration in the melt, one can obtain LiNbO₃ : Zn crystals with significantly different defect structures but identical zinc concentrations. A change in the zinc concentration in crystals has been shown to induce a stepwise change in the sequence order of the main (Li and Nb) and doping (Zn) cations and vacancies and stepwise anisotropic expansion of the oxygen octahedra along the polar axis. The number of kinks in the concentration behavior of the spectral-line widths (five kinks for the lines with frequencies of 630 (A₁(TO)) and 876 cm^–1 (A₁(LO))) significantly exceeds the number of thresholds (two) known from the literature.

Detection of phase-modulated signals generated by mechanical oscillations of a transparent object (plane-parallel glass plate) is considered. The signal is measured with the aid of interferometric system that employs nonsteady-state photo-EMF in adaptive photodetector based on the β-Ga₂O₃ crystal. A mechanical system consisting of a glass plate and a piezoelectric transducer exhibits resonance at a frequency of about 100 kHz. The amplitude of phase modulation has a bell-shaped distribution over the plate surface in the frequency interval under study. The parameters of the adaptive photodetector are determined for a radiation wavelength of λ = 532 nm.

The photoluminescence of the epitaxial structures based on the narrow-gap CdHgTe solid solutions has been experimentally investigated and the presence of large-scale composition fluctuations localizing carriers in the structures has been established. A model has been proposed for describing the effect of the fluctuations on the radiative recombination rate, the shape of the luminescence spectra, and their peak position. The model describes carrier transport and recombination at the strongly inhomogeneous composition of the solid solution and demonstrates the manifestation of carrier localization in the luminescence spectra.

A simplified model consisting of a laser diode, air gap, and optical fiber is used to calculate power and spectral characteristics and the band width of the radiation of laser with fiber Bragg grating. The results of the simplified model are in reasonable agreement with the experimental data on power and spectral characteristics. The radiation band width of the laser diode with fiber Bragg grating can be less than the band width for a single laser diode by four orders of magnitude.

Spectral dependence of the absorption coefficient of the CdSe_xS_{1 – x} nanocrystals in silicate glass with different perfections of crystalline lattice is experimentally studied. A dependence of the concentration of defects on the time of thermal processing is obtained. It is demonstrated that the defect elimination results from thermal activation process.

We have reported on the results of an investigation of the damping of longitudinal and shear hyperacoustic waves in Al/ZnO/Al/ZnO/YAG structures (lutetium-doped yttrium–aluminum garnet) based on ZnO piezo-active films with straight and inclined textures, which are synthesized at substrate temperatures T ≈ 25–400°C in an unbalanced planar magnetron sputtering system. It has been shown that anomalously high values of damping up to 45 dB is observed for the passage of acoustic waves through ZnO films with straight textures, which are grown at a substrate temperature T ≈ 200–300°C; an increase in the deposition temperature to T ≈ 400°C leads to a decrease in the introduced acoustic losses by 30–40 dB.

Electric field excitation by a horizontal flooded source placed at the interface between two media has been considered. A solution to the problem has been represented in the form of integrals that contain a quickly oscillating Bessel function. Under the quasi-static approximation, general functions that describe a field in water have been represented using the Watson integrals through the well-studied modified Bessel functions. It has been shown that, in the region at a distance more than a skin-layer from the antenna, the vertical component is determined by the field that propagates exclusively in the lower medium, and components perpendicular to the antenna have the form of the waves that propagate in the upper medium without absorption and then penetrate deeply, changing by the exponential law.

A study has been carried out of the electron-optical properties of improved design of the cylindrical mirror energy analyzer. Both external and internal electrodes of the analyzer are divided into three isolated parts, whereby the potentials on the individual parts can be regulated independently from each other. In symmetric operating mode at identical potentials on the side parts of the electrodes, a significant increase has been obtained in resolving power and light-gathering power of the analyzer compared to the standard design of the cylindrical mirror. In asymmetric operating mode, which is implemented in a linear potential distribution on the external electrode, the conditions have been found under which the linear dispersion of the analyzer increases several times.

Here we explore possibilities of the detached eddy simulation models (DES-models) in relation to a human nasal cavity as to a complicated structure of variable section with several bulges and irregularities (paranasal sinuses and turbinate). The three-dimensional geometric model (3D-model) of nasal cavity is perfomed on the results of the computer tomography with the Mercury Amira soft. The convective flows in the 3D-model are given with the Ansys Icem CFD soft. First-ever the nonstationary flow calculations for the 3D-model simulated nasal cavity are performed which aren’t averaged in time, and consider the function of pressure drop in breathing. The results of the simulation are compared with the experimental data obtained for the analogous solid 3D-model.

It has been established from a theoretical and experimental analysis of aerodynamic characteristics of acoustically modulated gas jets that, in the subcritical flow regime, acoustic vibrations affect the turbulent jet divergence at the exit from the jet–acoustic generator. It has been proved that the acoustic action on the core of a turbulent jet results in the hysteresis in the jet–acoustic system. This effect has been substantiated theoretically and the influence on the density of the reflecting surface on the hysteresis loop width has been confirmed experimentally.

We have analyzed the modification of the texture of polymer particle surface in a dust plasma. Monodisperse spherical melamine formaldehyde particles were injected into the glow discharge plasma in neon. At a certain discharge current and gas pressure in the discharge tube, the particles were suspended in dust-plasma traps and experienced the action of the plasma of 5–25 min. Then, the particles were extracted and the collected material was studied using the scanning electron microscope. Among the results, a change in the diameter and roughness of the surface depending on the residence time of particles in the dust plasma was established. It was found that the absolute deviation of all points of the surface profile averaged over the evaluation length were in the nanometer range. The time of complete degradation of particles in the experimental conditions has been established.