Home – Home – Jornals – Advanced Search

The development of a single thermal disturbance in a laminar boundary layer at a Mach number M = 1.43 in the presence of a pressure gradient induced by a shock wave emanating from a wedge with an angle of 2° is investigated using direct numerical simulation. Calculations are performed using the HyCFS-R code developed at the ITAM SB RAS. The evolution of the disturbance is examined in a zero-pressure-gradient boundary layer, during passage through the interaction region, and in the wake. A single thermal disturbance is shown to generate a localized wave packet. Spectral analysis is used to determine the packet composition and its evolution through the interaction zone. The influence of the pressure gradient on disturbance amplification is assessed, and the disturbance development in the boundary-layer-shock-wave interaction region up to the onset of laminar-turbulent transition is analyzed. A comparative analysis is performed for two types of boundary conditions applied at the lateral boundaries of the computational domain. The results show that the combined effect of the thermal disturbance and the shock wave plays a dominant role in boundary-layer destabilization, which should be taken into account in transition control strategies for supersonic flows.

A specialized experimental facility developed by the authors is described. The facility enables in vitro blood flow studies in vascular sections of various configurations while maintaining similarity to real hemodynamic conditions. Results of its performance evaluation are presented. The facility is shown to have several advantages over existing analogs. It enables flow visualization and measurements of flow parameters under both steady and pulsating conditions. The facility produces a waveform that matches the actual blood flow variation over a cardiac cycle, including a high-amplitude antegrade flow peak and a retrograde flow (flow rate reversal) segment. It also demonstrates stability and high reproducibility of the specified operating conditions. Experimental results obtained with this facility can be used to validate existing and future numerical models of vascular hemodynamics.

The process of blood pumping through an artificial vessel using a vibro-volumetric perfusion pump is investigated. The device is essentially an expanding channel with vibrating walls, approximating a diffuser in its simplest form. The relationship between the vibration parameters and the geometric characteristics of the device and the flow rate of transported blood is examined. A mathematical perfusion model is presented. This model incorporates a three-component rheological model of blood and a two-mass model of the oscillatory system of the device. The interaction between the vibrating walls, the deformable vessel, and the blood are also accounted for in the model presented.

The results of experimental studies aimed at determining methane formation mechanisms in the aerobic plant phyllosphere and the contribution of vegetation to global methane emission are reviewed and summarized. Until recently, methane formation and emission by biogenic sources had been associated exclusively with activities of methanogenic archaea growing under anaerobic conditions of water bodies and streams, swamps, rice fields, dumps, and the gastrointestinal tract of animals and termites. However, as demonstrated by modern data, methane formation is also possible via not only the microbial route, in the aerobic plant phyllosphere. Although the mechanism of anaerobic methane formation in plants is not clearly identified, the interconnection between the observed liberation of methane by plants and UV radiation impact and other physiological stresses (temperature change and plant physical trauma) recorded on the example of numerous experimental works demonstrates that this is a general process occurring in the presence of oxygen. It is considered that during UV radiation impact and other physiological stresses on plants, chemical reactions with the formation of oxygen active species start and consequently, some amount of methane is liberated from methoxyl groups of plant pectins (and according to some data, also from plant cellulose and lignin) as part of cell dissolution process. Using very diverse approaches, it is estimated that the most probable range of total methane emission by vegetation is 20-60 Tg/yr. Herewith, the fraction of foliar methane emission related to ultraviolet irradiation of pectin does not exceed 5% of global methane emission by vegetation, ~60% of which falls on tropical latitudes.

The effect of surfactants on the rate of the target reaction of tellurium precipitate from alkaline tellurium solutions and the side reaction of further reduction to ditelluride anions, and also current efficiency and morphology of cathode tellurium precipitates is examined on a graphite electrode pre-coated with tellurium sludges by the voltammetry method. Sodium lignosulphonate and polyvinyl alcohol have a weak effect on the rates of both cathode reactions and therefore on morphology of tellurium precipitates, as demonstrated. Tetrabutyl ammonium hydroxide additive inhibits both reactions but simultaneously worsens the quality of cathode precipitate: there generated a powdery sludge that is partly poured out from the substrate and is almost completely rinsed away upon water washing. The most efficient additive to obtain dense tellurium precipitates is OP-10 wetting agent. It substantially inhibits tellurium deposition and suppresses the side reaction of its dissolution in the virtually important range of potentials until the maximum current. At the same time, OP-10 significantly improves precipitate morphology and ensures obtaining fine-crystalline dense cathode tellurium precipitates.

The paper presents results of comparative study of composition and structure of nitrogen-containing resin bases of heavy oil from the Usinsk field before and after thermal effects at 450 ^oС for 30 min. Different molecular mass nitrogen-containing bases are isolated using sedimentation methods with hydrogen chloride and sulphuric-acid extraction from initial and thermolised resins. High molecular mass compounds comprise the bulk of bases in both cases, however, their fraction in thermolysed resins is substantially lower. Thermally transformed bases have lower masses compared to the initial ones. Structural group analysis and gas chromatographic mass spectrometry techniques examine the composition of the isolated compounds. Middle molecules of nitrogen-containing resin bases of both types consist of polycyclic rings that include aromatic and saturated cycles with different alkyl frames, as demonstrated. Average species of thermolysed resin compounds are more aromatic due to a decrease in the fraction of naphthene and alkyl fragments. In the composition of bases of initial and thermolysed resins, there are alkyl derivatives of quinoline, benzoquinoline, dibenzoquinoline, and azapyrene, the maximum of the distribution of which falls at alkylbenzoquinolines. The fraction of alkylquinolines is elevated among azaarenes of thermolysed resins. A higher fraction of structures with a lower number of carbon atoms in alkyl substituents is typical for all types of bases of thermolysed resins. It may be assumed that the identified compounds would enter into the composition of distillate fractions during thermal processing of heavy hydrocarbon raw materials. This is necessary to consider in solving issues related to preparation of high-quality fuels and lubricants based thereon.

The results of the study of chemical and phase compositions, IR spectroscopy analysis, morphology, specific surface area, pH of aqueous extract, and magnetic susceptibility of vermiculite samples from the Koksharovsky deposit of Primorsky Krai (the mineral, concentrate, and intumesced product) are presented. Comparative analysis of samples of vermiculite from Koksharovsky and Kovdor deposits of different origins was carried out.

Properties of anticorrosive coatings based on water-dispersive copolymers pigmented with manganese species were studied. It was found that the inclusion of the synthesized pigments into the composition of coatings elevated their ability to suppress underfilm steel corrosion. The compositions of anticorrosive primers that exceeded industrial analogues according to the efficiency of protective action were proposed.

Efficient nanocontainers based on noncovalent electrostatic complexes, such as sulfonated calix(4)resorcinol - cationic surfactants (CR - CS) with regulated solubilization and catalytic activity, were developed. Mono-, di-, and tetra-quaternized derivatives of 1,4-diazabicyclo(2.2.2)octane were used as CS. Reaction kinetics for hydrolysis of esters of acids of phosphorus, namely, 4-nitrophenyl-O-ethyl chloromethyl phosphonate, in the presence of CR - CS mixed compositions was studied by UV spectroscopy method during variation in the number of cationic centres of CS and addition of a hydrophobic dye (Orange-OT). Reaction parameters (the specific reaction rate in the micellar phase, substrate binding constant with aggregates, and the critical micelle concentration) attest to the fact that CR - mono-cationic surfactant system has the maximum catalytic activity.

The effect of heavy high molecular mass components of crude oil (asphaltenes, resins, and aromatic hydrocarbons) on its aggregative stability was studied on the example of heavy oils from the Usinsk field. The componential composition of oil samples was determined by precipitation and chromatography methods. Different spectral characteristics in the visible region that allow operatively comparing the resistance of crude oil against precipitation of asphaltenes were determined by the method of electron spectroscopy. For this purpose, dynamic curves of a change in the optical density were removed in solvent/precipitator (toluene/hexane) system and light absorption (C₅₀₀) and colour (Cc) coefficients were computed. The stability of crude oil was determined by not only the ratio of resin and asphaltene components, as demonstrated. Oil aggregative stability versus the degree of condensation and a network of aromatic compounds was revealed using colour coefficient.