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Using LA ICP MS dating of zircons, the age of the tuff (633±7 million years) of the Bolshoi Patom Formation at the base of the Vendian reference section in the south of the Siberian Platform (Ura Uplift) was estimated. The Vendian of the Siberian Platform was found to include the last Cryogenian (Marinoan) glaciation, and the postglacial sequence of the Vendian corresponds to the Ediacaran. In light of the obtained dating, the chronostratigraphy of the Riphean-Vendian deposits on the Ura Uplift and in adjacent areas is considered. The available geochronological and sequence stratigraphic data indicate the presence of hidden stratigraphic unconformity above the glacial horizon at the base of the Vendian, caused by glacio-isostasy.

The mechanism of longitudinal vortex formation in a supersonic jet issuing from an axisymmetric radial nozzle is investigated. Numerical simulations of the gas flow reveal that these vortices arise when gas flows from the prechamber into the inlet channel through a series of holes in a direction perpendicular to the axis of symmetry of the radial nozzle. The resulting vortices are then transported by the gas flow from the inlet channel into the radial nozzle and subsequently into the supersonic jet emanating from the nozzle. The numerical results are in satisfactory agreement with experimental data.

An original method for constructing a model porous medium is proposed. The approach is based on a well-known and widely used capillary model that accounts for pore-size distribution. The porous medium model is constructed by dividing the medium into thin layers perpendicular to the assumed flow direction, with capillary segments whose characteristics are determined using standard core analysis methods. The layers are probabilistically interconnected, forming parallel capillaries with variable cross sections. Within the inertialess flow approximation, the effective diameter of the capillaries is calculated. A pair of connected capillaries of different diameters is then replaced by a new capillary with this effective diameter. After repeating this operation iteratively, the original porous medium is represented by a bundle of parallel capillaries of uniform diameter. The theoretical aspects of the method are described, the adopted assumptions are substantiated, and the limitations of the model's applicability are identified. Results of absolute permeability calculations for two rock samples are presented and compared with those obtained using the classical capillary model. The proposed model is shown to provide a more accurate match between calculated and experimental data.

A method for controlling aerosol dispersion by applying ultrasonic vibrations of varying intensity is theoretically substantiated. Depending on the frequency and intensity of the ultrasonic field, either particle coarsening or fragmentation can be induced in the gas-dispersed system. A mathematical model for the coagulation and fragmentation of aerosol droplets in an ultrasonic field is developed. For the first time, a coagulation-fragmentation criterion ( t_CF ), defined as the ratio of the characteristic times of these two processes, is proposed. An expression for the critical particle diameter at which the characteristic times are equal ( t_CF = 1) is derived.

The distributions of velocity fluctuations in a Hagen-Poiseuille flow are obtained experimentally for various Reynolds numbers and pipe diameters. The longitudinal velocity fluctuation distribution is found to peak on the axis and to be independent of the Reynolds number. As the Reynolds number increases, the turbulence intensity in the tube decreases, while the root-mean-square value of the fluctuations increases. Velocity fluctuations (less than 2%) in the Hagen-Poiseuille flow are shown to have virtually no effect on the jet outflow from long pipes.

Full Navier-Stokes equations are applied to identify two branches of viscous flow regimes in the form of steady traveling waves between two smooth surfaces. The existence domain of the new solutions is determined on the parameter plane (wavelength and Reynolds number), and the flow regimes corresponding to one of the branches are shown to be unstable. Stable regimes exist over a wide range of Reynolds numbers, starting from values significantly lower than the Reynolds number at which the linear stability of the base steady-state solution is lost. The main wave characteristics of the new-type solutions are calculated. Achieving these solutions requires a pressure drop substantially greater than that needed for the base steady-state solution, while also resulting in enhanced heat transfer from the walls.

A numerical study of the effect of a perturbation generated by a vortex-generator fin on the local flow structure and turbulence of a bubbly flow in a planar channel behind a backward-facing step is performed. An Eulerian approach is employed to describe the flow dynamics and heat and mass transfer in both the carrier gas and dispersed phases. The problem is solved using the Reynolds-averaged Navier-Stokes equations, modified to account for the presence of bubbles. The influence of air bubble concentration, initial bubble diameter, and vortex generator height on the turbulent flow structure and the length of the separation region is investigated. The presence of the vortex-generator fin induces a significant (twofold) increase in the turbulence level in both single-phase and two-phase bubbly separated flows. The fin is found to exert a substantial effect on turbulence in the separated flow, with the turbulence level increasing by up to 60%. The addition of bubbles reduces the recirculation zone length (by 60% for ∆/H = 1/3).

A model for coupled axial-torsional oscillations of a drill string in a borehole of arbitrary profile is proposed. A numerical solution scheme is developed. A comparative analysis of the simulation results and field test data is performed. The main factors influencing the onset of stick-slip oscillations are identified as the intrinsic specific energy of rock destruction and the rotor speed. Comparison of the calculated results with field measurements demonstrates the adequacy of the model, with an accuracy acceptable for practical applications.

Results of an experimental study on the acoustoelasticity arising from the propagation of ultrasonic Rayleigh surface waves in a field of static bending stresses are presented. For a St. 20 steel specimen, the acoustoelastic effect is shown to differ under compression and tension. A calibration curve is constructed for Rayleigh surface waves, enabling their use for monitoring bending stresses-a capability not possible with bulk wave probing.

A gravity-based hydrodynamic flow loop capable of generating both steady and unsteady flow conditions is presented. The setup achieves velocities up to 16 cm/s and pressure fluctuations in a range of 60-130 mmHg within the measurement zone, enabling hemodynamic studies of virtually any segment of the cardiovascular system. For the first time, flow rate control is achieved by varying the angle at the junction of the systolic and diastolic flow circuits of the loop. Independent control of the minimum and maximum pressure in the unsteady flow is also implemented.