Vol 62, No 4 (2017)

A set of nonlinear differential equations that describe the dynamics of atomic–molecular conversion under the action of two arbitrarily shaped Raman pulses of resonance laser radiation has been derived in the mean-field approximation. The dynamics of the system subjected to Gaussian pulses has been studied in detail. It has been shown that the time evolution of the system depends on the initial conditions.

The magnetic properties of magnetic fluids based on n-undecane have been presented. The temperature dependences of the magnetic susceptibility in the absence and presence of a bias field have been analyzed. A step change in the specific heat of the medium, which is characteristic of magnetic phase transitions, has been discovered.

The problem about the average velocity of electrons in the cathode fall region of a glow discharge during nitriding has been solved theoretically and verified experimentally. The technique and analytical apparatus for practical calculations of the average electron velocity have been presented.

We have analyzed the effect of elastoplastic cyclic straining on anisotropy of elastic properties of 08Kh18N10T metastable austenite steel. The possibility of determining the strain amplitude of the fatigue loading cycle by an acoustic method involving measuring the elastic characteristic of the material has been demonstrated. The resulting experimental dependences that can be used to estimate the number of cycles before failure using ultrasonic measurements have been revealed.

Dynamic spalling tests have been run on two batches of 30KhN4M steel samples. Experimental data have been processed with the classical technique based on solution of the elastic wave equation. Three samples have been revealed that demonstrated the failure-delay effect under testing. The incubation-time criterion has been used to show the conditions of emergence of failure delay with the example of triangular loading pulses. A rate strength curve has been constructed for the other samples. It has been shown that the limiting strengths under dynamic loads considerably differ for samples from different batches despite the same chemical composition and static strength.

The conditions of the occurrence and development of thermal instabilities in the composite superconductor with a continuously increasing current-voltage characteristic, which is described by the power equation, have been studied. The conditions for thermal stabilization have been analyzed in the general form using dimensionless variables that keep their invariance when varying. For the local temperature disturbance, the critical energies and velocities of its irreversible propagation have been calculated. It has been proved that composites superconductors can have stable states, when the ultimate currents can be higher or lower of the conventionally preset critical current of the composite. Furthermore, superconductivity destruction at supercritical currents takes place not in the form of a stepwise transition from the superconducting to normal state, but due to the formation of thermal and electric switching waves that propagate along the composite superconductor with a constant speed. The condition for full thermal stabilization has been formulated for the superconducting composites with a power current–voltage characteristic. The results of the numerical experiments have proved that the existing theory of thermal stabilization, which assumes a stepwise superconducting–normal transition, leads to the considerable limitation of the range of the stable currents, at which a superconducting state can be kept.

A comprehensive analysis of the structure, phase composition, surface topology features, and magnetic and magnetocaloric properties of Tb_0.3Dy_0.35Ho_0.35Co_1.75T_0.25 (T = Al, Fe) multicomponent alloys has been performed. The specifics of variations in the structure and functional properties induced by the partial substitution of cobalt atoms in the 3d sublattice of RCo₂ with aluminum or iron atoms have been determined.

The present work is devoted to determining the conditions of the joint operation of photoelectric converter–solar concentrator pairs, which are used in solar power plants with concentrators. Three-cascade photoconverters based on A³B⁵ materials with different distributions of solar radiation in spectral ranges are studied. Concentrators of solar radiation are designed as the Fresnel lenses with silicon-on-glass structure. Refractive lens profile fabricated on the basis of Wacker RT604 silicone rubber is characterized by significant changes in refractive index with temperature. The effect of geometric parameters of the Fresnel lenses and their operating temperature on characteristics of solar radiation concentration in specified spectral intervals have been examined. The parameters of concentrators being paired with a photoelectric converter, which may ensure the efficient functioning of the solar power plant, have been calculated.

The shape of X-ray diffraction epitaxial layers with high dislocation densities has been studied experimentally. Measurements with an X-ray diffractometer were performed in double- and triple-crystal setups with both CuK_α and MoK_α radiation. Epitaxial layers (GaN, AlN, AlGaN, ZnO, etc.) with different degrees of structural perfection grown by various methods on sapphire, silicon, and silicon carbide substrates have been examined. The layer thickness varied in the range of 0.5–30 μm. It has been found that the center part of peaks is well approximated by the Voigt function with different Lorentz fractions, while the wing intensity drops faster and may be represented by a power function (with the index that varies from one structure to another). A well-marked dependence on the ordering of dislocations was observed. The drop in intensity in the majority of structures with a regular system and regular threading dislocations was close to the theoretically predicted law Δθ^–3; the intensity in films with a chaotic distribution decreased much faster. The dependence of the peak shape on the order of reflection, the diffraction geometry, and the epitaxial layer thickness was also examined.

The use of spray drying to obtain powders of complex oxides with a garnet structure has demonstrated. The processes occurring during heating of the synthesized oxide–salt product, leading to the formation of a material with a garnet structure, have been investigated using DTA, TGA, XPS, and XRD. It has been shown that a single-phase garnet structure of system (Y_xGd_(3–x))₃Al₅O₁₂ can be synthesized over the entire range of compositions.

A solution to the Sommerfeld problem of the far (in terms of wavelengths) field of a vertical electrical dipole placed at the interface between two media has been found. The characteristics of a surface electromagnetic wave that propagates over a medium with highly inductive surface impedance δ have been determined. The spatial characteristics of the wave are expressed through the real and imaginary parts of impedance δ. It has been proved that the surface electromagnetic wave is the major contributor to the electromagnetic field of the ground wave in the case of highly inductive radio paths.

An analysis of the stability zones of a linear ion trap in the case of applying the voltage of the common form to the electrodes has been presented. The possibility of the localization of ions for specific types of periodic (but not harmonic) signals has been investigated. It has been shown that, when changing the types of temporal functions of the applied voltage the control by both trapping and dynamics of ions in a linear radiofrequency (RF) trap occurs, while preserving its design. The latest developments present new possibilities of implementing devices based on single ions, e.g., quantum frequency standards and quantum processors.

The results of calculations related to designing an ultracold neutron source with superfluid helium for the WWR-M reactor have been presented. The ultracold neutron production rate has been estimated for different types of premoderator chamber filling. The dependence of this rate on the temperature of helium has been determined. If the premoderator chamber is filled with liquid orthodeuterium, the ultracold neutron production rate remains almost constant in the range of helium temperatures of 1.0–1.5 K and is as high as 3.1 × 10³ cm^–3 s^–1.

The optimal number of method for estimating and controlling the characteristic parameters (energy E_D and frequency ν) of dipole relaxation has been determined using the theory of thermostimulated depolarization currents. Along with the known method for estimating energy E_D from the slope of the initial segment of the curve describing thermostimulated depolarization currents, these techniques include another method for determining frequency ν proposed in this study, as well as the method for estimating parameters E_D and ν by fitting the experimental and calculated spectra of thermostimulated depolarization current, and the diagram of characteristic dipole parameters E_D and ν (which is universal for the entire set of electrets) and the corresponding spectra of thermostimulated depolarization currents.

The method of differential scanning ellipsometry has been used to study the influence of heating on the rhombic shape of paracetamol molecular crystals. Rhombic molecular paracetamol crystals have been synthesized in vacuum from the vapor phase of paracetamol as a result of complex transformation, which includes a second-order transition that gives rise to a pretransition phase. It has been found that these crystals contain monoclinic nuclei, which favor the form I-to-form II polymorphic transformation during heating.

We have reported on the results of experiments on the influence of current pulses on the band formation and intermittent deformation of AlMg5 alloy. It has been established that, to suppress the nucleation of deformation bands, preliminary treatment of the alloy by a current of density 60 A/mm² for at least 1 s is required.