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This special issue of the journal, dedicated to the memory of Academician Nikolai Leontievich Dobretsov, features articles reflecting the development of his research and ideas in areas within his scientific interests. The diversity of N.L. Dobretsov's scientific interests determined the broad range of topics covered in the articles presented. This range encompasses tectonics, deep geodynamics, the interaction of plate tectonics and plumes, metamorphism, including ultrahigh-pressure metamorphism in subduction zones, structural patterns of geomagnetic and gravitational fields and their relationship to plume magmatism, and unique mineral deposits.

Natural diamonds are polygenic and form over a very wide range of P-T parameters, crystallization medium compositions, and oxygen fugacity. As has been demonstrated in recent years, the genesis of some diamonds is directly related to their crystallization from metal-carbon melts. Since natural mineral-forming processes are highly likely to involve various components characteristic of mantle environments, it is relevant to analyze the results of experiments on the influence of fluids of the C-O-H-N-S system on the crystallization features and indicator properties of diamond. The experimental data presented in this review demonstrate that increasing the concentration of fluid components (N, O, S, H₂O, CH₄-H₂) at constant P-T parameters inhibits diamond crystallization processes in metal-carbon melts and ultimately leads to the formation of metastable graphite instead of diamond. Increasing P and T reduces the inhibitory effect of impurities and expands the diamond crystallization region. The main patterns of specific changes in the morphology, defect-impurity composition, and internal structure of diamond crystals are revealed, depending on the type and concentration of impurity in the crystallization medium. It is demonstrated that impurity-induced specific changes in diamond morphology and trends in nitrogen concentration in diamond are indicative of crystallization conditions and provide a basis for reconstructing diamond formation processes under reducing conditions in the metal-bearing mantle.

The study of the composition and crystallization conditions of olivine in kimberlites is of great importance for understanding the processes of their petrogenesis and predicting diamond potential. The aim of this study is to investigate the origin of the least studied generation of this mineral – late high-magnesium olivine. The material for the study consisted of samples of unaltered kimberlites from the Udachnaya-East pipe, where all generations of olivine are preserved. Results from scanning electron microscopy and microprobe analysis showed that high-Mg olivine exhibits the following variations in chemical composition: Mg# (Mg/(Mg+Fe²⁺)×100, mol. %) 93.3-98.7, 0.01-0.05 wt. % NiO, 0.12-1.88 wt. % CaO, 0.18-0.94 wt. % MnO. This olivine forms a paragenetic association with late magmatic minerals of kimberlites: magnetite, perovskite, apatite, monticellite, sodalite, phlogopite, djerfisherite, and calcite. The following forms of high-Mg olivine were identified: individual grains (the first finding in kimberlites), rinds, daughter phases within melt inclusions, phases in fractures earlier olivine generations, and in the interstices of microxenoliths. It was found that its crystallization occurred from alkaline-carbonate-chloride melts. The temperatures and oxygen fugacity values of the crystallization of high-Mg olivine can be estimated semi-quantitatively at 670-780 °C and +3.6 - +7.4 log. units ΔQFM.. The obtained data indicate that such olivine crystallized from evolved kimberlitic melts, which contradicts previously proposed models suggesting the formation of this olivine from fluids or during the serpentinization of kimberlites.

The results of direct numerical simulation (DNS) of the influence of a horizontal surface temperature gradient on the dynamics of a thermal convective flux are presented. A series of simulations was performed at moderate Rayleigh numbers (10⁵ - 10⁸). The computational domain was rectangular and its two horizontal walls had a specified average temperature difference, leading to the formation of a free-convective flow. The temperature on the lower wall was nonuniformly distributed along one of the horizontal axes. Convective cells formed due to the vertical density gradient were subject to a weak horizontal temperature gradient, which led to their deformation and transfer toward the central axis of the computational domain. As a result, intense coherent horizontal oscillations in the position of the central upflow at a low frequency were observed. This frequency depended weakly on the Rayleigh number, and the oscillation amplitude increased with its increase. This low-frequency oscillation effect is not evident in two-dimensional modeling and arises from the interaction of adjacent three-dimensional convective cells entering the central upflow. The authors propose an asymptotic estimate for the period of these oscillations. It is shown that the oscillations do not disappear with increasing Rayleigh number, suggesting their influence on heat and mass transfer in natural flows.

The main goal of the study is an experimental investigation of the mechanism of weakly nonlinear interaction of low-amplitude unsteady modes of crossflow instability in the boundary layer on a 35-degree swept wing with steady vortices of crossflow instability. The dominating factor in the flow under study is crossflow instability, while the Tollmien-Schlichting instability is suppressed by the favorable pressure gradient. High-amplitude steady distur-bances (up to 20% at the end of the measurement region) are excited by a surface roughness element. Controlled low-amplitude unsteady disturbances are generated in the boundary layer by a source of disturbances located upstream from the roughness element. Their amplitude in the main interaction region does not exceed 1%. The source excites quasi-two-dimensional (spanwise-uniform) waves at low frequencies corresponding to the primary crossflow instability region. The results of hot-wire measurements show that the characteristics of the mean flow, as well as of steady and unsteady disturbances are independent of the disturbance amplitude. However, the evolution of unsteady disturbances is strongly affected by the presence of vortices. The excited quasi-two-dimensional instability waves rapidly decay in the downstream direction, while the forming and growing (in a certain range of transverse wave numbers) steady vortices transform two-dimensional waves to essentially three-dimensional waves with the transverse wave spectrum corresponding to the most rapidly growing crossflow instability modes. This transformation does not occur locally, in the near field of the surface roughness, but is distributed in the streamwise direction. The amplitudes of steady disturbances grow almost exponentially, with the growth rate depending on the transverse wave number in a manner typical for crossflow instability modes. The growth of the amplitudes of unsteady modes exhibits a more complicated, sometimes nonmonotonic character owing to their nonlinear interaction. It is found that the amplitudes of unsteady disturbances of all frequencies in the plane normal to the flow and the wall are strongly localized in regions of high values of the mean flow velocity gradient over the model span. An essentially three-dimensional physical mechanism of weakly nonlinear transformation of quasi-two-dimensional wave disturbances to three-dimensional waves by high-amplitude steady instability vortices is proposed, which is similar to the lift-up effect used previously to explain the growth of streaky structures in two-dimensional boundary layers.

The experimental results on the swirling flow structure behind a vane swirler in a smooth tube at an axial flow Reynolds number varying within Re = 240 - 1640 are presented. A change in the degree of flow swirl along the tube length is analyzed as a function of the Reynolds number. The main patterns in the evolution of the profiles of longitudinal and circumferential velocity components and the distribution of the mean square pulsations of the longitudinal velocity component with increasing distance from the swirler are determined. It is shown that at Re = 1640, flow instability develops in the tube, which is a consequence of the formation of a reverse flow region on the tube axis in the immediate vicinity of the swirler. The influence of flow swirl on the appearance of signs of a local laminar-tur-bulent transition in vicinity of the tube axis and near its wall is analyzed (a sharp increase in the mean square velocity pulsations with increasing Reynolds number and the appearance of intermittency in the flow velocity oscillograms). It has been established that in the near-wall region, local turbulence of the flow is caused by the interaction between the swirler vane wakes and the wall.

Methodical issues associated with investigations of the laminar-turbulent transition in subsonic boundary layers with the use of video filming in the infrared range are considered. A method of estimating the wall friction based on the analysis of the temperature behavior of the heated model surface is proposed. An improved method of finding the lines of transition beginning and end is proposed.

The paper considers a possibility of controlling the structure of a fluoropolymer coating by diluting the precursor gas with an inert gas during synthesis by the Hot Wire Chemical Vapor Deposition method (Hot Wire CVD). Dilution of the precursor gas significantly affects the morphology of the formed coating and alters the coating wettability and the growth rate.

The dynamics of a slug flow in immiscible liquids remains incompletely understood due to the complex effects of channel geometry and the properties of the working fluids. The presence of surfactants in the system further complicates the problem. This work deals with the effect of an water solution of Tween 20 surfactant on the dynamics of a slug flow in a curved microchannel. Situations with surfactant concentrations below and above the critical concentration of micelle formation are considered. Regime maps are plotted, and three regimes of water phase dispersion are identified. It is shown that increasing the surfactant concentration leads to stabilization of slug interfaces in straight sections, while the probability of slug disintegration in curved sections increases due to reduced interfacial tension and intense mixing of the surfactant within the slugs. The decisive influence of the surfactant concentration relative to the critical concentration of micelle formation on the dynamics of microdroplet detachment processes in straight and curved sections of the channel is revealed.

The paper describes experimental results on the action of weak shock waves on the development of controlled disturbances in a supersonic boundary layer on a flat plate at the Mach number of 2.0, which are obtained by measurements performed by a constant-temperature hot-wire anemometer. A two-dimensional surface roughness element 150×7×0.13 mm in size, mounted on the side wall of the test section of the T-325 wind tunnel based at ITAM SB RAS, generated a pair of weak shock waves in the free stream. Controlled disturbances are inserted into the flow by a high-frequency glow discharge in a chamber inside the model. Owing to interaction of the pair of weak shock waves with the leading edge of the flat plate, a steady wake is formed in the boundary layer, where the evolution of controlled disturbances occurs. A weakly nonlinear regime of evolution of controlled disturbances is studied under the conditions of a homogeneous boundary layer on the flat plate and a boundary layer distorted by the wake. The wave characteristics of disturbances are analyzed. A new method of estimating the dispersion relation is proposed. The experimental data are compared with the numerical results. Numerical simulations are performed based on the liner stability theory under the conditions of a homogeneous boundary layer.