Vol 509, No 1 (2023)

The minimal values of the electric 2.45 GHz microwave field, which are necessary to maintain a discharge in a number of noble gases (argon, neon, and helium) in optical fibers with hollow cores of small diameter up to 100 μm, have been measured for the first time. The minimal electric field values for all three gases are (2.5–2.8) kV/cm at a pressure of argon ~50 Torr, neon ~300 Torr, and helium ~500 Torr.

We present the results of magmatic aerosol concentration monitoring carried out utilizing an aerosol lidar. The monitoring was performed in a hot dead-end tunnel of the Baksan Neutrino Observatory (BNO) of the Institute for Nuclear Research located above the Elbrus volcanic center’s small magma chamber. An abrupt 3-fold increase of the aerosol concentration was detected by the lidar on October 28, 2019, 22: 30 UTC in the hot tunnel of BNO. The lidar data were analyzed along with the data of radon volume radioactivity, air temperature and relative humidity sensors. Synchronous changes in the air temperature, relative humidity and aerosol concentration have been observed, as well as the correlation of these signals with Earth’s crust deformation measured by a strainmeter installed in BNO. However, neither one of these signals reflected the detected 3-fold aerosol concentration growth. The acquired data confirms the existence of a hot magma chamber found earlier under the Andyrchi mountain by the small-aperture seismometer group. A possible explanation of the 3-fold aerosol concentration growth is discussed: emanation of gases from the magma chamber could trigger this growth without influencing other measured parameters.

It is known that in wall-bounded flows, along with the growth of instability modes, the non-modal (algebraic) mechanism of linear growth plays an important role. In open flows, including submerged jets, the non-modal growth mechanism is theoretically studied only in the last decade; this mechanism has not yet been identified in experiments. In the present work, experiments on excitation of a non-modal “lift-up” growth mechanism are conducted. Special wavy structures (deflectors) are introduced into a laminar submerged jet of circular cross section, which excites a roller-like transverse movement. The data obtained unambiguously identify the non-modal “lift-up” growth of introduced disturbances. The development of perturbations in the experiment qualitatively corresponds to the theoretically calculated optimal perturbations. The features of the transition to turbulence caused by non-modal growth are considered.

The field of attraction of a rigid body is studied. It is assumed, that the body is close to dynamically symmetric one. The problem of approximation of body’s field of attraction by the field of attraction of three homogeneous balls is considered. The goal of such approximation is to provide coincidence of the terms up to the fifth order of smallness in the series expansions for gravitational potentials of the body and three balls. As an example, the approximation of asteroid (433) Eros by three balls is considered.

In the present work, under the assumption of smallness of deformations, bending-torsional characteristics and angles of rotation (including the angles of free rotation) of the elements of the plate, based on the three-dimensional geometrically-nonlinear moment theory of elasticity, preserving only those nonlinear terms, that come from normal displacement (deflection) and its derivatives, a geometrically nonlinear moment-membrane theory of elastic plates is constructed as a continual theory of deformations of a flexible graphene. For the indicated nonlinear theory of elastic plates, by introducing stress functions, the resolving equations are presented also in a mixed form: these are the system of equilibrium equations for transverse-bending deformation, compiled in the deformed state of the plate, and deformations continuity equations, expressed in stress functions and deflection functions. For the geometrically nonlinear moment-membrane theory of elastic plates Lagrange-type variational principle is established.

The 3D problem of elastic wave scattering by a crack in the form of a half-plane in an elastic medium is considered. It is noted that the previously published solutions do not fully cover the issues relevant to ultrasonic flaw detection, for example, to detect transverse cracks in welds. The proposed solution is made by the Wiener–Hopf tecnique. It is shown that scattered longitudinal and transverse waves can be generally written in the closed form. Some features of the identification of the tip of transverse cracks are noted, including scattering features during sonication of cracks along their surface and the influence of critical angles.