Doklady Physics

To achieve the thermonuclear-ignition threshold in the scheme of indirect X-ray irradiation of the Z-pinch, it is necessary to implode the liner by a current with an amplitude of ~65 МА within a time of ~100 ns. Currents with such parameters can be generated using super-power disk-type explosive magnetic generators and a two-stage current pulse-sharpening system based on foil, electrically exploded, “serpentine”-shaped current opening switches. It is reasonable to implement the explosive current source with a rise time of ~100 ns in stages by increasing the current magnitude. The results of the first-stage experiments in which a current with an amplitude of 5 MA is used in an inductive load of ~10 nH with a time of ~120 ns on the basis of the helical explosive magnetic generator are given.

In this paper, we numerically solve the problem of detonation formation resulting from free flame propagation in an unconfined space. The mechanism of detonation formation that reduces to the local formation of shock waves during the development of the linear stage of unstable growth of disturbances formed on the surface of an expanding flame front is described. The basic criteria for creating conditions for the transition to detonation by the mechanism described are also formulated.

The regularities and mechanisms of coalescence of Au nanodroplets and sintering of solid Au nanoparticles are investigated using molecular dynamics experiments and some theoretical models. It is established that the characteristic time of coalescence τ is proportional to the radius r₀ of the original nanodroplets. Both the conclusion and the quantitative estimations of the proportionality coefficient between τ and r₀ agree with Frenkel’s theory (1946), yet this theory was proposed for describing the coalescence of macroscopic droplets.

On the basis of the laws of conservation and the principles of thermodynamics, a mathematical model of the flow of a two-phase granular fluid is proposed. One of the phases is the viscoplastic granular Bingham fluid; the other phase is a viscous Newtonian fluid. The equations for flows in the Hele–Shaw cell are analyzed asymptotically, i.e., when the flat-channel width is much less than its length. The correlations between the phase flow rates and the pressure gradient leading to equations of filtration for a two-phase granular viscoplastic fluid are constructed. The criterion is found for the initiation of motion of a granular phase in a porous medium. It is established that, depending on the shear-yield stress, such a phase does not flow if either the pressure gradient or the channel thickness is small. The phase flow rates are analyzed numerically at various input parameters such as the phase viscosities, phase resistivities, ultimate shear stress, etc. The factors slowing down the penetrating motion of the solid phase into the porous medium are revealed.

The influence of the planets of the Solar System on the precession of the orbit of Mercury is investigated in the framework of classical mechanics. The influence of each planet on the motion of Mercury is calculated in the context of a restricted problem of three bodies: the Sun, the planet in question, and Mercury. It is demonstrated that the average shift of the perihelion of the orbit of Mercury determined in the context of a planar circular restricted three-body problem is 556.5″ per century and agrees with the observed shift (570″) with a relative accuracy of 2.5%. It is also demonstrated that the observed perihelion shift of Mercury features oscillatory components with a total amplitude up to 20″ and periods from several years to several decades. Owing to the presence of these components, the perihelion shift rate calculated based on observations conducted for several tens or even hundreds of years may differ considerably from the true average rate. This is likely the reason why the calculated average perihelion shift rate is not completely consistent with observational data.

A new physical (experimental) model of cavitation destruction of the materials studied is proposed. In the modern model of the cavitation effect, the destruction of materials is associated with the impacts of cumulative jets, which are formed during the asymmetric slamming of cavitation bubbles near the solid surface, and the shock waves that occur during their compression. In the new model, erosion damage is explained by the formation of cavitation tubes (с-tubes) with a spiral high-frequency structure in the materials under consideration, and these tubes were previously unknown in the literature. The destruction of materials is associated with the focusing of acoustic energy along the axis of the spiral structures. When the energy is focused, there is a significant increase in the pressure and temperature along the axis of the spiral structures, which leads to the destruction of the materials under study.

Integrability is shown for certain classes of ninth-order dynamic systems homogeneous on the part of variables in which a system on the tangent bundle to the four-dimensional manifolds is singled out. In this case, the force fields have dissipation of different signs and generalize the situations considered previously.