Doklady Rossijskoj akademii nauk. Fizika, tehničeskie nauki

This article reports the results on development and study of the output characteristics of bismuth-doped fiber lasers for the near-IR range, which are pumped into a cladding using multimode laser diodes emitting at a wavelength of 808 nm. The active medium of such lasers was bismuth-doped germanosilicate glass fibers with various shapes (circular and square sections) of the inner cladding coated with a polymer having a refractive index of 1.396. On the basis of such fibers, a series of lasers generating radiation in the wavelength range 1.4–1.5 μm was developed, and their spectral and power characteristics were studied. Numerical simulation was also carried out aimed at finding the optimal configuration of such lasers in order to determine the maximum achievable characteristics of these devices. A good agreement between the calculated data and the experimental results has been obtained. As a result, using a bismuth-doped active fiber with a square cross section of ~80 μm and a core diameter of ~11 μm, a fiber laser was created that operated at a wavelength of ~1460 nm, with a slope efficiency of about 5% and a maximum output power of more than 250 mW.

Ice is a complex heterogeneous medium. Its behavior depends on many factors and changes in different processes. Thus, the problem of the determination of the correct rheological model is still unsolved. In this work low-speed impact on ice by the ball striker is considered. The main focus of the research is the development of the method of the correct model selection based on the computer simulation of the laboratory experiment. The simulation was conducted using the following rheology models: isotropic linear elasticity model, elastoplasticity model with the von Mises and the von Mises-Schleicher yield criteria, elasticity model with elastoplastic inclusion. The governing system of equations is solved using grid-characteristic method. Models’ comparison is performed based on the ball’s velocity and depth of ball’s immersion into the ice. The model parameters’ influence on the results is surveyed. As a result, the parameters that reconstruct the solution close to the experimental results are chosen.

Experimental and theoretical studies of the magnetic properties of the unique Ising-like paramagnet (La_0.985Ho_0.015)₃Ga₅SiO₁₄ have been carried out. We found magnetic anisotropy in strong magnetic field (up to 5 T) rotated in the ab*, b*c and ac planes at low temperatures (T ≤ 5K). We show that the observed magnetization features are connected with the local orientation and distribution of the Ho³⁺ Ising axes, which may deviate from the symmetry-allowed directions due to Ga/Si random filling in the local environment of the magnetic ions.

The results of experimental studies of the effect of residual magnetization on the corrosion of steel samples in an aqueous medium are presented. Algorithms of research and processing of results are described. Three cases of initial magnetization of samples are considered. It is established that before the critical magnetization of steel samples, the corrosion wear in the aqueous medium decreases, and then begins to grow. The discovered effect is of great theoretical importance in studying the phenomenon of corrosion, taking into account the initial residual magnetization, as well as of great practical importance, in particular, in the design and operation of various structures and structures made of steel to protect them from corrosion destruction.

An approach is proposed to analyze one of the most critical stages of spacecraft operation – the soft landing process, starting from the moment of the first contact of the spacecraft with the ground to its complete stop. It is noted that it is necessary to extinguish the significant kinetic energy that the device possesses at the moment of contact with the surface. The most common type of landing device is considered spring-lever type, including several supports with deformable energy absorbers. Limited opportunities for ground-based experimental testing of the soft landing process lead to the need to use a dynamic model to analyze the success of landing and rational selection of the characteristics of the landing device. The model of the landing process is based on the representation of the vehicle body and its landing device elements as a structurally complex mechanical system of bodies with internal connections, the type of which is determined by restrictions imposed on the relative movement of the system bodies. An approach to the for-mulation of special equations for determining bond reactions that reflects these limitations is presented. The success criteria of the landing process are described. The success analysis of the planting process is illustrated by a specific example.

It is known that the flow of liquids with a nonmonotonic dependence of viscosity on temperature (abnormally thermoviscous liquids) in the presence of temperature gradients, for example, when a heated liquid flows into a cooled channel, is accompanied by the formation of a high-viscosity region localized in the flow, which determines the features of its flow. In this paper, the conditions for the occurrence of self-oscillating regimes of flow rate variation during the flow of anomalously thermoviscous liquids in annular channels under the action of a constant pressure drop and under given conditions of heat transfer on the inner and outer walls of the annular channel are determined. It has been found that self-oscillations in the flow rate of an anomalously thermoviscous liquid can occur when flowing in an annular channel, on the walls of which there is an abrupt decrease in the intensity of heat transfer. The region of existence of the self-oscillation mode is determined by the values of the pressure drop and the geometric parameter equal to the ratio of the width of the annular gap to the radius of the inner cylinder. In addition, weakly damped flow rate oscillations with a very small damping decrement were also observed at the boundaries of this region.

Tidal Love numbers are often used for studying the interior structure of planets and satellites of the Solar System. Measuring the deformation in response to tidal loading belongs to the methods for probing the interiors. The algorithm for computing tidal deformation depends on a series of assumptions and approximations and, therefore, can differ according to different authors. In this paper we compare the existing methods and, based on them, we propose a new and more precise algorithm for computing the tidal Love numbers of the Earth and other bodies with a similar interior structure.

On the secluded interface of semi-infinite magnetic and non-magnetic media, hybridiza-tion of magnetoelastic interaction with inhomogeneous exchange or magneto-dipole interaction can lead to the formation of symmetry-protected bound states in the radiation spectrum of the leaky surface magnon polarons. If a quasi-plane bulk elastic wave falls on the surface of a magnetic medium from outside, and the wave parameters approach to the parameters of the surface “dark” state of the above mentioned type, the nonspecular reflection effects of the first order increase unrestrictedly (in the non-dissipative approximation).