Vol 58, No 11 (2016)

The contribution of the Coulomb exchange interaction between pairs of electrons found in one quantum state is calculated. For this case it is shown that in an unpolarized, degenerate, weakly nonideal electron gas the frequency of a Langmuir wave with zero wave vector is \( \sqrt{3/2} \) times greater than the Langmuir frequency. With increase of the spin polarization (with decrease of the number of pairs of electrons in one quantum state) the frequency shift decreases monotonically to zero.

An asymptotic expression for the vertex function in the region of large momenta in quantum electrodynamics is investigated in the ladder approximation. To formulate a calculational model in the ladder approximation, an iterative scheme has been used to solve the Schwinger–Dyson equation in the formalism of a bilocal source of fields. For the chirally symmetric leading approximation, the Edwards equation for the electron–positron–photon vertex has been obtained in the case of arbitrary values of the photon momentum. Our primary task is to develop a method to solve the vertex equation in the region of large momenta. Nontrivial behavior of the vertex function in the deeply inelastic region of momenta has been revealed.

The main characteristics of motion of an equilibrium system of potentially interacting material points in a nonuniform field of forces and the criteria determining the transition from discrete to thermodynamic system description are studied. A change in the internal energy of the system passing through a potential barrier is studied depending on the barrier width, the number of the system elements, and the initial conditions. It is demonstrated how the amplitude of fluctuations of the system energy parameters changes depending on the number of the material points. The D-entropy is evaluated. Two critical numbers are established. The first determines the number of the material points required for system transition to irreversible dynamics, and the second determines transition to the thermodynamic description. The conformity between the results obtained and the theoretical principles of system dynamics is analyzed.

The features of orientation dependence of stress-induced thermoelastic B2–(R)–B19′-martensitic transformations in single crystals of the Ti_48.5Ni_51.5 and Ni_51.0Ti_36.5Hf_12.5 (at.%) alloys, which contain disperse particles of the Ti₃Ni₄ and H-phase, respectively, are revealed along with those of their shape-memory effects (SME) and superelasticity (SE). It is experimentally demonstrated that irrespective of the crystal structure of disperse particles measuring more than 100 nm, for their volume fraction f > 16% there is a weaker orientation dependence of the reversible strain in the cases of manifestation of SME and SE. In the orientations of Class I, wherein martensitic detwinning introduces a considerable contribution into transformation strain, the values of SME |ε_SME| and SE |ε_SE| decrease by over a factor of two compared to the theoretical lattice strain value |ε_tr0| for a B2–B19′-transformation and the experimental values of reversible strain for quenched TiNi crystals. In the orientations of Class 2, wherein detwinning of the martensite is suppressed as is the case in quenched single-phase single crystals, the reversible strain is maintained close to its theoretical value |ε_tr0|. Micromechanical models of interaction between the martensite and the disperse particles are proposed, which account for the weaker orientation dependence of |ε_SME| and |ε_SE| due to suppression of detwinning of the B19′-martensite crystals by the particles and a transition from a single-variant evolution of the stress-induced martensitic transformations to a multiple-variant evolution of transformations in the cases of increased size of the particles and their larger volume fractions.

Using single crystals of Fe-based disordered alloys (Fe – 28% Ni – 17% Co – 11.5% Al – 2.5% Х (0.05% B) (at.%) (X = Ti, Nb(B), (Ti + Nb)B), undergoing thermoelastic γ-α′-martensitic transformations (MTs), it is shown that precipitation of particles of the ordered γ'-phase in the course of aging at Т = 973 K for 5 h results in the development of shape memory (SME) and superelasticity (SE) effects. It is experimentally found that variation in chemical composition and size of disperse particles of the γ'-phase allows controlling both mechanical and functional properties – SME and SE.

General points of the theory of isotope substitution are applied to an analysis of the isotope substitution effect for the substitution ¹³C₂H₄←¹²C₂H₄ in the ethylene molecule. On the basis of the isotope relations so obtained, numerical predictions of band centers and the most significant rotational, centrifugal, and resonance parameters are made here for the first time for the four lower vibrational states of the ¹³C₂H₄ molecule, which can be used to analyze the complicated vibrational-rotational structure of the above-mentioned vibrational states.

The spectrum of the ν₆ band of the cis-ethylene-d₂ molecule (cis-C₂H₂D₂) is recorded with a Bruker IFS 125 HR Fourier spectrometer in the range 580–1210 cm^–1 with resolution of 0.0021 cm^–1. An analysis of the experimental spectrum allows more than 1500 transitions belonging to this band to be assigned that by more than 2.5 times greater than it has been known in the literature so far. The obtained experimental data are then used to determine the model parameters of the molecule (the effective Hamiltonian in the A-reduction and I′- representation). Strong resonance interaction with the band ν₄ forbidden in absorption by the symmetry of a molecule is taken into account. 10 parameters of the Hamiltonian obtained by solving inverse spectroscopic problem reproduce 427 initial experimental energies (more than 1500 transitions) with accuracy close to the experimental uncertainty.

The method of pulsed laser ablation in liquid was used to synthesize dispersions of cerium oxide nanoparticles when subjecting a metallic cerium target in water and alcohol to basic frequency radiation of the nanosecond Nd:YAG laser (1064 nm, 7 ns, 20 Hz). Researchers have studied the effect of laser radiation parameters, duration of impact, and optical scheme of experiment on the ablation process. The average rate of nanoparticle production was 50 mg/h in water and 25 mg/h in alcohol. Researchers have studied the size characteristics and crystalline structure of the nanoparticles produced. The particles have bimodal size distribution with 6 nm and 25 nm maximums. The average crystallite size is 17–19 nm. The crystalline structure of nanoparticles, namely cubic cerium oxide (fluorite structure), space group Fm-3m, is confirmed by the X-ray diffraction data, as well as optical absorption spectra and Raman spectroscopy.

Analytical dependences of the equivalent circuit elements of heterostructures on the material properties of quantum wells, their location, and bias voltage of the heterostructure are obtained. On the basis of these dependences, expressions for calculating the dependences of the equivalent capacitance and equivalent resistance of the heterostructure on the test signal frequency and bias voltage are found.

Possibilities of reduction of the number of time variables in a timed automaton used for synchronization of components in physical systems, for example, lasers are investigated. Reduction of the number of time variables allows problems of testing of the components for compliance with requirement specification to be simplified.

A computational-experimental investigation of stress-strain state and fracture of a porous heterogeneous material with an inorganic matrix, used as a thermal barrier coating of flying vehicles, under conditions of a high-velocity impact by a spherical steel projectile imitating a meteorite particle is discussed. Ballistic tests are performed at the velocities about 2.5 km/s. Numerical modeling of the high-velocity impact is described within the framework of a porous elastoplastic model including fracture and different phase states of the materials. The calculations are performed using the Euler and Lagrange numerical techniques for the velocities up to 10 km/s in a complete-space problem statement.

Effect of volume discharge plasma initiated by an avalanche electron beam on the composition, structure, and properties of the surface steel layer is investigated. Voltage pulses with incident wave amplitude up to 30 kV, full width at half maximum of about 4 ns, and wave front of about 2.5 ns were applied to the gap with an inhomogeneous electric field. Changes indicating the hardening effect of the volume discharge initiated by an avalanche electron beam are revealed in St3-grade steel specimens treated by the discharge of this type.

Conditions are described under which films of [(aminophenyl)azo]pyridine are formed by molecular layer epitaxy, and their optical absorption and x-ray photoelectron spectra are investigated. The nonlinear properties of such structures are described with the help of measurements of the intensity of second harmonic generation as a function of the angle of incidence.

An analysis of experimental data revealed the dependence of the metal/n-GaN GaN(0001) barrier height on the metal work function, as predicted by the model that takes into account the charge neutrality level of the semiconductor. In case of the metal/p-GaN(Mg) barriers, significant scatter of the corresponding experimental data is observed and pinning of the near-surface Fermi level near E_v + 2.5 eV takes place in most structures, which is due to the influence of high density of interface defect states formed during the process of the GaN doping by Mg impurity.

A flow of physical events (photons, electrons, etc.) is studied. One of the mathematical models of such flows is the MAP-flow of events. The flow circulates under conditions of the unextendable dead time period, when the dead time period is unknown. The dead time period is estimated by the method of maximum likelihood from observations of arrival instants of events.

It is experimentally demonstrated that the longitudinal thermal diffusion autosoliton formed in a nonequilibrium electron-hole plasma in p-InSb in an external longitudinal magnetic field acquires diamagnetic properties. Results of calculation and numerical estimates of diamagnetism are given.