Vol 63, No 6 (2018)

The discovery of stimulated Raman scattering (SRS) in monoclinic fluoride β-BaYb₂F₈ known as a host matrix for Ln³⁺ lasant ions was reported. All the recorded spectral components of Stokes and anti-Stokes χ⁽³⁾-nonlinear picosecond generation were assigned to the three SRS-active photon A_g- and B_g-modes of a crystal (ω_SRS1 ~ 362 cm^–1, ω_SRS2 ~ 295 cm^–1, and ω_SRS3 ~ 230 cm^–1).

The main optimal signal processing operation is shown to be the division of the energy estimates for the random processes observed in the adjacent time intervals. It is justified that this processing may be deemed the primary one and it is necessary to introduce the secondary processing - averaging the unbiased primary estimates of the effective noise temperature. The potential fluctuation sensitivity of the radiometer and the limiting errors of the joint estimates of the noise temperature and the gain instability parameter have been determined.

The structure of twisted flow in a Ranque−Hilsch vortex tube is investigated experimentally by modeling gas flow with an incompressible fluid flow. The velocity field is measured with a laser Doppler anemometer in the entire volume of the vortex chamber. The streamline pattern, which gives a complete presentation of the flow structure in the Ranque−Hilsch tube, is plotted in the axial section of the chamber. The resulting streamline pattern can serve as a basis for explaining the physical mechanism of the Ranque effect.

The effect of mean excessive pressure on the cylindrical bending of a plate is studied. An increase in this pressure leads to a decrease in deflection and vice versa. In the first case, the plate shape is stabilized under the action of longitudinal forces; in the second case, it is destabilized. The critical value of the mean pressure, upon achieving which an unlimited increase in the linear solution takes place, is determined. The dependence of the effect of the mean pressure on the bending on the boundary conditions, as well as on the ratio of pressures at the surface of the plate and at its edges, is shown.

The dynamics of a lattice structure consisting of strings and point bodies at the places of their intersection, as well as limiters that can be struck by these bodies (nodes), is investigated. Equations of motion are given, and methods for their solution are pointed out. In particular, the existence of standing waves characterized by synchronous impacts of all nodes in the power excitation mode is experimentally established. The results of analysis of such movements are presented.

The properties of the solution to the well-known problem of the optimal orientation of a satellite in the plane of a circular orbit and its steering to a gravitationally stable angular position, which was posed and considered earlier by Vladimir V. Beletskij, have been refined. The constraint on the control torque module is considered as the main parameter of the problem. It turned out that, even in the case when the admissible control torque exceeds the gravitational moment in magnitude, in the phase plane the existence of additional switching curves corresponding to relay control with two switchings is possible. As a result, a simple numerical algorithm is proposed, and with its help the threshold absolute control value is found at which the indicated switching curves are infinitesimal, and their coordinates in the phase plane are found.