Doklady Physics最新文献

Local thermal perturbations in supercooled glass-forming liquids during the nucleation and decay of nuclei of the crystalline phase are analyzed. The nonequilibrium thermal response of glass-forming materials to fast local thermal perturbations is described using an integral equation with dynamic heat capacity. It is shown that local thermal perturbations associated with the formation of nuclei of the crystalline phase significantly affect the nucleation rate in supercooled glass-forming liquids. The obtained fundamental knowledge can be useful for the technology of new nanostructured materials, polymers and nanocomposites.

The giant microwave magnetoresistance effect for the reflection of waves from the superlattice (CoFe)/Cu-substrate system is investigated. The reflection–coefficient dependence on the strength of the magnetic field is measured within the frequency range of 26–38 GHz. The nonreciprocity of the wave reflection is revealed, which can enhance the giant effect of microwave magnetoresistance.

A new method for changing the spatial orientation of a rigid body by means of several movable point masses is proposed. It is assumed that these masses form three pairs, and the masses of each pair move symmetrically to each other. It is shown that, under the assumptions made, any given motion of the body can be implemented, including a plane rotation around an arbitrary axis. Two versions of the algorithm are proposed.

In this paper, we propose to use thermal-protective respirators based on granular phase change materials to protect the respiratory organs from dangerously high temperatures of inhaled air during fires and other emergencies. We demonstrate the possibility of creating such personal protective equipment based on known materials using a numerical experiment. In this case, the insignificant mass of the cooling element based on granular phase change material makes it possible to combine it with a gas and smoke protective element and create combined respirators that protect against both high temperatures and toxic combustion products.

A multichannel uncontrolled discharger based on staged breakdown of a multilayer film insulator with an enclosed foil plate under floating potential has been developed. An abrupt change in the foil potential after a single-channel initial self-breakdown between the foil and one of the electrodes leads to a multi-channel secondary breakdown between the foil and the other electrode. Cumulative plasma jets are generated in places of breakdown and they initiate the formation of the through current channels between the electrodes at the third stage of the breakdown. The developed multichannel discharger has a nanosecond response time and can be used to sharpen the voltage pulse front in the electric-discharge devices with megaampere currents. A similar method of formation of a multichannel breakdown can be used in the development of nanosecond switches of multimegaampere currents in the directions of thermonuclear research with the use of explosive magnetic energy generators.

A controlled (variable) rate of mass discharge generated by the mechanism of using the internal energy is postulated for a space body with variable composition. Based on this postulate, equations of the dynamics without external forces are derived within the special theory of relativity, the solution of which makes it possible to study crucial rocket dynamics and astrophysics problems over the entire physical range of speeds of motion.

Wave pattern analysis of the interaction of an elongated impactor with a target allowed us to establish a number of previously unknown features of the process. The entire length of the impactor can be divided into sections where the wave pattern repeats the initial phase of the impact, while the role of the target is played by the impactor material. Throughout the entire process of interaction of the two bodies, the mass velocity and the pressure behind the shock wave front moving along the side face have constant values equal to (0.25–0.32) of the initial value. The cycle itself is characterized by two stages. At the first stage, the convergence of the lateral unloading waves on the contact surface leads to the establishment of zero pressure, a layer of unloaded material is formed between the shock waves in the target and the impactor, while the impactor penetration stops. A needle-like crack along the symmetry axis appears as a result of focusing the unloading lateral waves. The second stage is characterized by shock wave attenuation. The incoming flow, the velocity of which is equal to the impact velocity, is braking at the attenuation wave front, which leads to an increase in pressure and the formation of compression impulses. The arrival of compression impulses on the target restores the interrupted process of the impactor penetration and creates new spall damage in the rings from around the needle-like spall, as a result of the unloading waves interference, the sources of which are the spall cracks formed earlier and the impactor side face.

The experimental data on low-temperature (T < 40 K) neutron scattering and electron paramagnetic resonance for a helical magnet manganese monosilicide (MnSi) are analyzed. It is established that the smooth evolution of the parameters of spin fluctuations considered both in the conventional theory of magnetic phase transitions and in its generalization to the case of helical magnets is disturbed by the presence of spin-fluctuation transitions (SFTs) in which the amplitude of spin fluctuations and their correlation radius change sharply. In a zero magnetic field, the transition at the temperature T_c = 29 K, which is usually interpreted as the transition to a helical magnetically ordered phase, is preceded by two spin-fluctuation transitions with T₁ = 32 K and T₂ = 30.5 K. In a magnetic field of B ~ 2 T at a temperature of 29 K coinciding with T_c, another spin-fluctuation transition with the parameters characteristic for the SFT inside the magnetically ordered phase is discovered. It is shown that, as the temperature decreases, MnSi at T = T₁ undergoes the SFT with the appearance of helical fluctuations, while the appearance of a helical phase (B = 0) or a spin-polarized phase (B = 2 T) occurs at T = T₂ and is accompanied by a spin-fluctuation transition.

This article is based on the annual reports presented by the Head of the Physical Sciences Division of the Russian Academy of Sciences at the General Meetings of the Division in April 2021 and April 2022. It describes some scientific results in physics obtained in 2020–2021 at the research institutions (institutes of the Russian Academy of Sciences) under the individual powers of the Russian Academy of Sciences stipulated by the regulations of the Government of the Russian Federation no. 521 dated June 5, 2014, and no. 1652 dated December 24, 2018. The information about the research in different fields of physics carried out at these institutions is summarized briefly and illustrated by examples of some bright scientific breakthroughs.

In this paper, we consider the nonclassical dam-break problem in a semi-open rectangular channel in the first approximation of the shallow water theory when the liquid is under the lid in the upper pool of the dam (i.e., it completely fills a semi-infinite rectangular container) and the liquid surface is free in the bottom pool. It is shown that there is a unique piecewise constant self-similar solution to this problem, in which the hydraulic bore in the bottom pool of the dam is modeled by a shock wave, the descent wave in the upper pool of the dam is modeled by a strong discontinuity (when passing through which the total energy of the liquid flow is conserved), while the flow in the region between the hydraulic bore and the descent wave is approximated by a constant solution. Experimental modeling of this problem will make it possible to obtain wave flows that arise when liquid flows out of a rectangular container, a special case of which is the classical Benjamin flow.