Doklady Physics最新文献

In this work, for the first time, an exact solution of the contact problem of interaction with a multilayer base of two semi-infinite stamps, the ends of which are parallel to each other, is constructed. The stamps are assumed to be absolutely rigid, and the distance between them can have any finite value. The task is an important stage in the algorithm for constructing models of a new type of crack in materials of different rheologies. The mechanism of destruction of the medium by cracks of a new type is radically different from the mechanism of destruction of the medium by Griffiths cracks, and has so far been little studied. Griffiths formed his cracks with a smooth border as a result of compression from the sides of an elliptical cavity in the plate. Cracks of a new type have a piecewise smooth border, resulting from the replacement of an ellipse with a rectangle compressed from the sides. The problem considered in this article can be considered as the result of the formation of a new type of crack with absolutely rigid banks and a deformable lower boundary. Thanks to it, after the solution, it becomes possible to switch to deformable stamps and a crack of a new type in the rheological medium. The solution of this problem turned out to be possible due to the construction of exact solutions of the Wiener–Hopf integral equations on a finite segment. This paper shows how the solution of one of the previously unsolved problems allows us to investigate and solve exactly other problems and to identify previously unknown properties and resonances. As a result of constructing an exact solution to the problem, the fact that the solution of dynamic contact problems for stamp systems is not unique was confirmed and a dispersion equation for finding resonant frequencies was constructed.

In this work, numerical experiments were carried out in the framework of the molecular dynamics method to study the impact interaction of metallic nanoclusters of different sizes with a metallic substrate in a wide range of velocities. Analysis of the data obtained showed that the crater volume remains proportional to the impact energy and inversely proportional to the dynamic strength of the material, with the line slope being independent of the cluster size and the cluster–substrate material.

A method for generation of ultra-wideband electromagnetic pulses with a nanosecond length and a picosecond rise time has been proposed and studied. A horn antenna with a photoconductive switch irradiated by laser pulses has been used as an emitter. It is shown that the length of ultra-wideband electromagnetic pulses is determined by the antenna length and the semiconductor material and the rise front is determined by the front of laser pulses used to initiate a photoconductive switch. Typical pulse lengths of ~1 ns with a rise front of up to ~34 ps are reported.

The experimental and calculated on the basis of density functional theory Raman spectra of plant and bacterial carotenoids (neurosporene, spheroidene, lycopene, spirilloxanthin, β-carotene, lutein, ζ-carotene, α-carotene, and γ-carotene) are analyzed. A number of characteristic features in the Raman spectra of carotenoids are described for the first time, which make it possible to determine the structure of the end groups of molecules and to distinguish their isomers.

In this paper, the rectilinear motion of a body controlled by moving internal mass in a medium with quadratic resistance is considered. The conditions under which the translational motion of a body occurs with periodically varying velocity are considered. The average velocity of this movement is determined. Conditions that provide the highest average velocity were established.

The basic principles of a thermal explosion had been studied and published by 1980. It seemed that the research was completed, but later it was discovered that Zeldovich’s “ignition condition” does not correlate with the experimental data. “The theory of ignition by a heated surface” is the basis of ignition theory, but, although the calculations are correct, the results obtained are mistakenly attributed to ignition—in reality they describe the spontaneous ignition of an infinite combustible. Our work shows that a thermal explosion of a combustible from a heated body can develop as ignition and self-ignition. The conditions for self-ignition of an infinite combustible by a flat surface and a cylinder are given, as is the likely condition for the ignition of a combustible between parallel walls of different temperatures.

A methodology for constructing three-dimensional shell models for the layer-by-layer study of the stress and strain state of irregular sandwich shells, which are increasingly used in practice, is proposed. An original approach is considered for obtaining approximating displacement functions in the finite elements of the core layer, which does not lead to a discontinuity in the generalized displacements on the interfaces with moment skin layers. The development of such models makes it possible to significantly expand the class of problems to be solved and, with the necessary accuracy and degree of detail, for the first time to study the stress and strain state in the general case of irregular sandwich shells in a wide range of variation in the geometric and physical and mechanical characteristics of the layers. The possibilities of the proposed methodology are illustrated by the example of the study of the stress and strain state of conical sandwich shells with rectangular cutouts.

An analytical dependence between the dimensionless coefficients of added mass and thermal conductivity was obtained in a suspension of spherical particles. The dependence is confirmed by comparison with the theoretical data of other authors, including at elevated concentrations of dispersed particles, taking into account their hydrodynamic interaction.

Samples of the Murchison meteorite (carbonaceous chondrite, type CM2) were kept isothermally in a specially designed device at temperatures of 200, 500, and 800°C. After the samples cooled down in an inert helium atmosphere, Raman scattering spectra were taken. An increase in the intensity of the G- and D‑lines of graphite was detected depending on the degree of heating. It is shown that using such a characteristic parameter of these lines as the area ratio, S_D/S_G, it is possible to define a geothermometer to determine the maximum temperature of thermal metamorphism of the parent bodies of carbonaceous chondrites. A comparison with the known data for carbonaceous chondrite Allende (CV3), which has experienced a significant thermal metamorphism, is carried out.

The derivation of the equation of static cylindrical bending of a thin plate under the action of pressures on its surface and end edges is given. The reduction over the thickness of the plate is taken into account, the effect of which becomes noticeable at high average pressure. The refined value of the transverse distributed force is used. The dependence of the bending on the average pressure and the rigidity of the supports in the longitudinal direction is considered.