Doklady Physics最新文献

The dynamic problem of thermoelasticity with a localized inclusion in a medium is considered. It is shown that in the resonant regime an important role is played by the coupling coefficient of the temperature and strain fields. The coupling of the problem and the presence of a discrete spectrum lead to the appearance of an additional term in the expression for temperature, which is localized and does not describe the diffusion process.

In conditions of high-temperature creep, the evolution of the damage of metallic materials is observed. To describe this effect, the damage conception of Kachanov–Rabotnov is used. The damage parameter is defined as the relative changes in the material density, which is an integral characteristic of the damage. Taking into account this parameter and the law of conservation of mass, interrelated kinetic equations for creep deformation and the damage parameter are formulated. Analytical solutions of these equations are obtained for the case of two-stage loading. Experimental studies of the uniaxial stress state under conditions of high-temperature creep under two-stage loading of the aluminum alloy ENAW 5251 (AMg2) at a temperature of 250°C were conducted. A good agreement of the obtained theoretical curves with the experimental results is observed.

The conditions and dynamics of electron runaway in a gas gap with an inhomogeneous electric field distribution due to the use of a conic cathode are analyzed. Significant distinctions in the behavior of electrons at cone opening angles larger and smaller than the threshold value of 98.6° are revealed. For a weakly inhomogeneous field distribution (cones with angles above the threshold), electrons are continuously accelerated throughout the entire gap. In a strongly inhomogeneous field (cones with comparatively small opening angles), electrons may gain a maximum energy within the gap and start to decelerate in the near-anode area. However, they reach the anode with high energies comparable to the electric field work. Such a difference necessitates the use of different criteria for the runaway of free electrons in the gas gap.

For the first time, in a single experiment, the dependence of the position of the phonon absorption peaks in the IR spectrum (range 11–40 μm) for all five stable monoisotopic germanium single crystals was studied. The dependence obtained can be used to study the mass composition of germanium of various isotopic purity.

Theoretical studies predict that the light magnetic doping of Dirac semimetals leads to the occurrence of extraordinary properties and quantum states, including the Weyl semimetal, axionic insulator, topological superconductor, and others. However, thespecific materials that can exhibit these phenomena, as well as the characteristic concentrations of magnetic atoms are still unknown. In this work, the ab initio study of the electronic and magnetic properties of the Cd₃As₂ Dirac semimetal doped isoelectronically with Mn atoms at concentrations of 4, 6, and 8% has been carried out. In the analysis of the results, the main focus has been on the break of the spatial and time symmetry in the alloys, the behavior of the electron spectrum near the top of the Dirac cone, and spin ordering processes in Mn atoms. The results obtained have been compared with the previous theoretical and experimental data and, based on these results, a detailed picture of the effect of isoelectronic magnetic doping on the properties of the Cd₃As₂ Dirac semimetal has been presented.

For the first time, the properties of the phase invariant of sound to vector–scalar fields formed in a waveguide by directional multipole sources are studied. It is shown that, when even such complex sources are used, the phase invariant is valid for sound pressure and for projections of the vibrational velocity vector. It practically does not depend on the directivity and frequency of the source, the distance between the receiver and the source, or on the parameters of the waveguide.

Forced nonlinear oscillations of a gas bubble in a liquid are investigated when the frequency of fluctuations in the external pressure of the liquid is equal to the natural frequency of the bubble (resonance). By the method of averaging, a simple formula is derived for the dependence of the oscillation amplitude of a gas bubble on the amplitude of the external pressure and the thermophysical characteristics of the gas and the viscosity of the liquid. Its good agreement with numerical calculations is shown up to the value of the oscillation amplitude of the bubble radius comparable to its equilibrium value.

A new architecture of photosensitive elements for the near- (0.7–1.4 μm) and short-wavelength (1.4–3.0 μm) infrared spectral ranges is proposed, which is based on hybrid nanostructures consisting of PbS colloidal quantum dots and ZnO and silver nanowire functional layers. Small-sized (12 × 12 μm) photosensitive elements with an energy barrier at the contact between layers of colloidal quantum dots with n- and p‑type conductivity have been studied. The I‒V characteristics, spectral dependences of optical absorption, and relative spectral photosensitivity S_i(λ)/S_i(λ_max) of the barrier structures at room temperature have been examined. It is shown that the proposed architecture of the barrier structures ensures the photosensitivity in a wide spectral range from 0.4 to 2.0 µm. An excess of the average value of the relative spectral sensitivity S_i(λ)/S_i(λ_max) by a factor of about 1.5 as compared with the values observed previously for the PbS colloidal quantum dot barrier nanostructures in the wavelength range of 0.9–1.85 μm has been found.

The chemical vapor deposition synthesis of periodic structures in the form of single-crystal diamond–SiO₂ nanosphere composites, which exhibit the properties of photonic crystals in the visible spectral range, are reported.

With the help of wire arc additive manufacturing, a high-entropy alloy of AlCrFeCoNi was prepared: of a non-equiatomic composition, on which a B + Cr film with a thickness of ~1 μm was deposited by plasma-assisted RF sputtering. Subsequent processing consisted in electron-beam irradiation of the surface with the following parameters: energy density 20–40 J/cm², pulse duration 200 μs, frequency 0.3 s^–1, and number of pulses 3. A quasi-periodic distribution of chemical elements (at %) 33.4 Al, 8.3 Cr, 17.1 Fe, 5.4 Co, and 35.7 Ni is established. It is shown that, at the energy density of the electron beam E_s = 20 J/cm², the microhardness increases by a factor of two and the wear resistance by a factor of five, and the friction coefficient decreases by a factor of 1.3. High-speed crystallization of the surface layer leads to the formation of a subgrain structure with subgrain sizes (150–200 nm). The increase in strength and tribological properties during electron-beam processing is interpreted taking into account the reduction in grain size, the formation of chromium and aluminum oxyborides, and the formation of a solid solution of boron incorporation into the HEA crystal lattice.