Home – Home – Jornals – Combustion, Explosion and Shock Waves 2023 number 3

The Salair fold-thrust orogenic belt (Salair orogen, Salair) is located in the northwestern Altai-Sayan fold area within the Central Asian Orogenic Belt. The Salair orogen is an allochthon overriding the Kuznetsk Basin on a system of imbricate thrusts. The southern flank of the Salair thrust system is tectonically juxtaposed against the Gornaya Shoria terrane which differs markedly from Salair in its geological setting. The Salair and Gornaya Shoria terranes are separated by the Nenya-Chumysh Basin, a deep Mesozoic trough. The Salair orogen is composed of Cambrian-Early Ordovician island arc volcanic and sedimentary rocks, widespread garnet amphibolites and gneisses of the Angurep complex in its southern flank, and the Shalap subduction-related melange in the Alambai ophiolite suture. The southern Salair orogen and its junction with Gornaya Shoria have been imaged down to the lower crust by magnetotelluric (MT) soundings, which is an efficient tool for investigating the deep structure and tectonic history of orogenic areas. The MT surveys were performed at 25 stations on a 120 km long profile. MT data revealed an up to 70 km wide low-resistivity zone (a conductor) traceable till a depth of 20 km between the Salair and Gornaya Shoria terranes. The low-resistivity zone has a complex structure with its outer and interior boundaries dipping almost vertically. The conductor lies under several major geological structures: the Shalap melange, the Nenya-Chumysh Basin, and the NE trending Altai-Salair right-lateral strike-slip fault. The Altai-Salair fault, along which the Salair allochthon was displaced relative to Gorny Altai and Gornaya Shoria, joins the Salair system of imbricate thrusts. The Nenya-Chumysh Basin at the Salair-Gornaya Shoria junction is a deep trough having an asymmetric transversal profile with a steep western side and a shallower-dipping stepped eastern side. The southeastern flank of the basin is a wide area of thin sediments over the Paleozoic basement dipping gently in the northwestern direction. The revealed deep structure of the Nenya-Chumysh trough is consistent with its tectonic model implying an Early Cretaceous basin superposed over an early Jurassic pull-apart basin. Early Mesozoic motions on major faults is a regional-scale phenomenon known from many areas of southern West Siberia.

The surface pattern of permafrost area in the Tibetan Plateau, with 15-20 m polygons, resembles the patterned ground of the Arctic periglacial loess plains in northeastern Eurasia and North America. However, unlike the Arctic plains, it consists of semi-stabilized modern sand dunes, up to 2.5-3.0 m high, and U-shaped epigenetic ice wedge casts inherited from an ancient polygonal network on the surface of a 10-12-m terrace of the Yangtze River. The polygonal dunes and the U-shaped sand wedges were studied in the Yangtze headwaters in the vicinity of the high-altitude research station Bei-Lu-Xe. The polygons have desert pavement floors with ventifacts, composed of Late Pleistocene alluvial gravel and debris. The dunes and wedges consist of well sorted quartz-carbonate sand with an average grains size of 2.0-2.2 mm. Ground Penetrating Radar surveys in the area revealed the permafrost table at depths varying from 2 m to 4 m below the dunes. The polygonal dunes may have formed by biogenic-aeolian deposition over an ancient system of ice wedges.

The rarely visited islands of the Kara Sea in its Pritaymyr zone have been studied during a geological survey on the scale 1: 1,000,000. The Quaternary deposits of the islands are represented by the Middle Neopleistocene to Holocene marine, lacustrine-marsh, alluvial and slope sediments. New radiocarbon and uranium-thorium dating has been obtained for the Quaternary sediments, using organic remains (wood, peat, mollusk shells). For the first time, dating on sandy sediments was obtained for the islands, using the method of infrared optical-stimulated luminescence (IR-OSL). The sediments of marine terraces are of the greatest distribution on the islands; these sediments can be correlated with the Karginsky (MIS 3) horizon, lacustrine-marsh sediments and deposits of the cover complex, containing flora remains, mainly the Holocene.

The paper focuses on the surface topography and deposits associated with the Late Pleistocene ice-dammed lake in the valley of the Kharal River dammed by the Azas ice sheet in a depression between the East Sayan and Akademik Obruchev Range. The study includes paleogeographic reconstructions for the time spans before the lake formation and drainage; reconstruction of vegetation in the lake area based on pollen and paleocarpological data; and dating by optically stimulated luminescence (OSL) and ⁴⁰Ar/³⁹Ar methods. The OSL and Ar-Ar dates provide more rigorous constraints on the history of deposition and topography in the western Serligkhem Basin. The territory was affected by erosion and subsequent basaltic volcanism at 6.9 ± 0.7 and 2.2 ± 0.7 Ma. The erosion valleys were dammed by the edge of an ice sheet and then by its moraine, which produced large Upper Kharal damlake. According to OSL data, the lake existed between 36 ± 4 and 14 ± 3 ka BP. The related glacial, glaciolimnic, and glaciofluvial facies in the area were deposited at the end of the Late Pleistocene (stages III and IV of regional stratigraphy).

Magnetic and density depth models were calculated for the Malmyzh, Pony-Muli, and Anadzhakan porphyry-copper ore clusters emplaced in the northern part of the Middle Amur sedimentary basin. Based on analysis of anomalous magnetic field (magnetic model) data, a magmatogenic ring structure determining spatial patterns in localization of porphyry-copper mineralization in the Malmyzh and Pony-Muli ore clusters was established. It is shown that similar structures in the anomalous magnetic field are reported for many porphyry copper deposits. The area of the identified geologic structure can be considered as a high-potential region for detection of gold-copper-porphyry ore mineralization. Within the ring structure, perspective areas containing granitoid and diorite intrusions developed along its periphery and seated beneath the Middle Amur basin sedimentary cover can also be identified. Geophysical depth models are calculated for individual ore clusters with Au-Cu porphyry mineralization, to determine subsurface lithology and structures that may be useful for assessing regional ore potential and deducing areas for metallogenic exploration. The geophysical data-based deep subsurface model for the Malmyzh ore cluster is found to be consistent with the integrated petrological models developed by J.P. Richards and R.H. Sillitoe for giant Cu-porphyry deposits.

Based on the analysis of the 2017-2021 recordings from the Kharino seismic station (the Altai-Sayan seismic stations network) and the 2002-2019 satellite imagery, the trigger of the July 18, 2020 earth-slide at Elbashinsky waste rock dump of the Kolyvan Anthracite Deposit (Novosibirsk region) has been established. The study of natural oscillations of the mine waste dump allowed estimating its stability and thus contributing to environmental and industrial safety in surface mining of solid minerals.

The paper describes the results of studying the influence of a free-stream disturbance localized in time and space on the structure of the wake behind a symmetric droplet-shaped airfoil in the range of angles of attack from -20° to +20°. It is demonstrated that the existence of such a disturbance leads to suppression of vortex formation at certain angles of attack. Ranges of angles of attack in which the wake structure remains unchanged are found.

This work is devoted to a numerical study of the influence of foreign-gas injection on the stability of compressible boundary layer on a concave surface. The stability calculation was carried out in the framework of the locally parallel linear stability theory. The results of calculations for the reference case without injection showed that Görtler vortices and the second Mack mode exhibited the highest growth rates at studied parameters. It is found that the injection of a heavy gas (with respect to the oncoming gas) leads to an increase in the rate of growth of Görtler vortices and the second Mack mode, whereas the injection of a light gas leads to a decreased rate of growth of these perturbations.

Based on photometric measurements in an argon flow, the influence of large van der Waals clusters on the transverse dimensions of a supersonic under-expanded jet was revealed. In the range of average sizes of formed clusters 330 < 〈S〉 < 6200 part./clust., a model of corrections to the known gas-dynamic empirical dependences, formed in the absence of a condensed phase, was proposed to take into account the features of gas outflow from a supersonic nozzle under developed condensation. The possible reasons for the broadening of gas flows under conditions of developed condensation were established. The proposed correction model was tested in supersonic outflows of condensing gas on a number of supersonic conical nozzles.

An experimental study of the influence of the leading-edge bluntness radius of a plate on the response of boundary layer on this plate to an N-wave at Mach number M=2 was carried out. Three flat-plate models with leading-edge bluntness radii r = 0.05, 0.5, and 2.5 mm were used in the experiments. The oncoming-flow disturbances were created using a generator installed on the sidewall of the test section of the T-325 wind tunnel of ITAM, SB RAS. It is found that behind the N-wave in the oncoming flow there forms an extended region with an increased level of flow pulsations whose spectrum features amplitudes increased both in the low-frequency and in the high-frequency portion of the spectrum compared to the undisturbed free flow. It was shown that, under experimental conditions, the flow non-uniformity generated by the N-wave can exert a greater influence on the laminar-turbulent transition in the boundary layer of a flat plate with an increase in the leading-edge bluntness radius.

The development of instabilities in supersonic perfectly expanded jets exhausting from nozzles with square and rectangular cross sections into an ambient flow is studied based on the numerical solution of the Navier-Stokes equations. The simulations are performed for various Mach numbers of the jet and the ambient flow. The results of numerical calculations make it possible to identify qualitative and quantitative differences in instability development in cases with supersonic and subsonic air flows, as well as characteristic features of the flow for rectangular jets.

This work is a continuation of a cycle of research by the authors aimed at studying the laws of liquid hydrocarbon combustion under steam supply conditions as applied to the development of low-emission burners. When simulating numerically diesel fuel combustion, n-heptane (formula C₇H₁₆) is used as a one-component analogue. Reliable experimental data are required to verify the obtained results. In this work, for the first time, the combustion parameters of n-heptane are experimentally studied when it is sprayed with superheated steam in a new laboratory atmospheric burner with forced air supply to the gas generation chamber. The calculation results are compared with data on diesel fuel. The performed comparison shows that the characters of gas component dependences inside the flame for diesel and heptane differ. This is primarily due to the different densities, viscosities of fuels, their flammability and burning rate (depending, among other things, on the forced supply of air (oxidizer)). At that, a quantitative comparison shows that the values of gas components at the flame boundary are quite close to each other. The effect of ongoing physicochemical processes in the presence of steam (gasification, hydrocarbon splitting, combustible mixture dilution, formation of active OH radicals) on the composition of final combustion products is higher than the effect of fuel properties. It is shown that during the combustion of n-heptane atomized by a steam jet, all the main features characteristic of diesel combustion with steam supply are retained. High completeness of fuel combustion and low level of toxic emissions into the atmosphere are ensured, which satisfies the European standard EN:267. With an increase in the share of steam in the combustible mixture, the tendency to a CO and NO_x decrease remains. The air flow control in the gas generation chamber of the burner allows further regulation of the level of toxic combustion products released into the atmosphere. The dynamics of dependences of CO and NO_x emissions repeats for heptane and diesel with some local differences. Also, the paper analyzes the correctness of n-heptane applicability for the problems of numerical simulation of diesel combustion in a steam jet with the indicated assumptions.

For the first time, experimental studies were carried out on the effect of hydrogen combustion inside a supersonic (М_е= 2) flat-plate boundary layer on the laminar-turbulent transition in this flow. It was found in experiments that hydrogen injection (originating from the streamlined model) and its combustion in a certain sublayer partly stabilizes the layer flow. This result corresponds to the calculated data from S.A. Gaponov: it was shown that the heat supply into the supersonic boundary layer can deter the disturbance growth (i.e., facilitates the stabilization of the boundary layer stabilization). However, in general (compared to the non-combustion flow), the supersonic boundary layer is destabilized by combined hydrogen injection and fuel combustion. This means that the destabilizing effect of hydrogen injection prevails over the stabilizing effect of heat supply to the boundary layer.

The effect of the parameters of a pulsed-periodic side jet on combustion of a hydrocarbon fuel in an axisymmetric channel flow with the Mach number of 1.7 is studied numerically. The Reynolds-averaged Navier-Stokes equations closed with the k-ε turbulence model are solved. Fuel combustion is modeled with the use of one reaction. It is demonstrated that the temperature of the gas generator for the jet produced only a minor effect on the shock wave structure of the flow. The key role belongs to the pressure of side jet injection. A transonic flow structure is obtained.

The paper presents a numerical simulation of a stagnant (suspending) gas slug in the Taylor flow fitted to the experimental conditions. The simulation is based on the unsteady model of k - ω SST (shear stress transport) turbulence. Simulation covers analysis of gas-and-liquid flow parameters in the zones ahead the slug, after the slug and for the liquid film. The study demonstrates a compliance between the experiment results and simulation regarding the liquid film shear stress, the slug nose shape and the film thickness.

The effect of the parameters of a pulsed-periodic side jet on combustion of a hydrocarbon fuel in an axisymmetric channel flow with the Mach number of 1.7 is studied numerically. The Reynolds-averaged Navier-Stokes equations closed with the k-e turbulence model are solved. Fuel combustion is modeled with the use of one reaction. It is demonstrated that the temperature of the gas generator for the jet produced only a minor effect on the shock wave structure of the flow. The key role belongs to the pressure of side jet injection. A transonic flow structure is obtained.

This study seeks to improve the film cooling performance by embedding a film hole in a V-shaped trench. The angle scale that makes up the V has been changed, 25°, 75° and 115°. The three novel designs were compared to rectangular (transverse) trench and conventional cylindrical hole. The main parameters of film cooling, cooling effectiveness, and total pressure loss, were discussed at three blowing ratios, M=0.5, 1.0, and 2.0. Fifteen cases were simulated using Reynolds averaged Navier-Stokes equations closed by the RNG k-ε model. A good agreement is obtained between CFD results with experimental data of the baseline case. The results showed that the use of compact jet in the trenches, whether transverse or V-shaped, enhances the film cooling effectiveness. The use of V-shaped trench helps to reduce the size of the kidney vortices (CRV) and, thus, enhance the film cooling performance. The V2 shaped trench is the most prefer in improving the film cooling efficiency and reducing the total pressure loss.

The paper presents a developed 2D mathematical model for a regenerative heat exchanger designed for a ventilation system operating with a periodic change in airflow direction. This kind of ventilation system saves the heat energy required for heating of domestic premises during a winter season. Results for calculations by a two-dimensional model are compared with one-dimensional modeling and with available experimental data. The authors formulated a definition of energy efficiency in terms of reduction in heat losses. Our calculations demonstrate that the efficiency of a regenerative heat exchanger might exceed 90 %. The numerical simulation was applied for parametric study of this problem; we revealed the influence of the heat exchanger operational and design parameters on the energy efficiency. Numerical experiments found a group of parameters most significant for energy efficiency of ventilation system; recommendations on system optimization were formulated.

The influence of the size of water droplets, temperature, and velocity of a streamlining jet of dry air on the rate of evaporation is considered. Due to the systematic studies using a thermal imager, it is shown that the interface temperature changes spontaneously. It is assumed that the temperature nonuniformity on the surface is caused by the release of vapor nanobubbles and can be characterized by the velocity of their outflow. Empirical regularities on the intensity of bubble release from a droplet are obtained both as a function of time and diameter, and in the criterion form.

The gasification of solid urotropine was experimentally studied at filtering a high-temperature flow of carbon dioxide through it. It was shown that with an increase in the temperature of the filtered gas from 650 to 920 K, the time of urotropine gasification decreased and the average gasification rate increased from 0.38 to 1.25 g/s, leading to an increase in the flow of urotropine gasification products. The maximum achieved value of the mass of urotropine gasification products was 0.8 g per 1 g of incoming gas. In the temperature range of 480-530 K, intensive gasification of urotropine occurred, while the temperature of the gaseous products leaving the reactor remained practically unchanged. The amount of noncondensable gaseous gasification products did not exceed 1% of the initial mass of the sample.

The object of an experimental study is a vapor bubble formed in a subcooled liquid as a result of absorption of laser radiation transmitted into the working volume through a thin optical fiber. Evolution of a bubble is characterized by its rapid growth and collapse with generation of a hot submerged jet. Some features of the process under study are considered in relation to the field of medicine. Normal saline is used as the working fluid. It is shown that under the same conditions (radiation power, optical fiber diameter, and initial temperature of liquid), the dimensions reached by a vapor bubble in saline solution are much smaller than those in pure water. A significant influence of the shape of a fiber tip on the nature of the process under study was revealed.

This paper considers the microwave processing for snow-ice mass comprising the heating and melting stages. The search for basic patterns of these processes aimed to optimization, control and design of stages is based on mathematical models and their implementation using analytical or numerical methods. A nonlinear mathematical model of the two-phase Stefan problem for a layered system of dielectrics was constructed. This approach takes into account the dependences of the medium permittivity and other parameters on the medium temperature and the design of a microwave radiation source.

Thin films of polycrystalline silicon are widely used in semiconductor industry. One of the methods for obtaining such structures on cheap and low-melting substrates is metal-induced crystallization, since the use of a metal (for example, Au) as a catalyst during crystallization of an amorphous semiconductor allows a considerable reduction of annealing temperature. However, the typical duration of metal-induced crystallization is several tens of hours, in contrast to the method of laser-induced crystallization. In the present work, for the first time it is proposed to combine the advantages of the laser-induced and Au-induced crystallization methods. The authors have identified laser-processing modes of thin films of non-stoichiometric silicon oxide (a-SiO_0,1) using nanosecond radiation with a wavelength in the infrared range which ensure the formation of polycrystalline silicon.

In this work, the thermal conductivity of refrigerants systems from three different hydrofluoroolefins including R1234yf, R1234ze (E), and R1233zd(E) were studied using artificial neural network. A total of 4395 data points of liquid and vapor thermal conductivity at several temperatures (241.92 to 344.46) K and pressures (0.068 to 21.73) MPa were used to train and test the model. Five neurons were used in the input layer, fifteen neurons at hidden layer and one was used in the output layer. Bayesian Regulation back propagation algorithm, logarithmic sigmoid transfer function, and linear transfer function were used at the hidden and output layer, respectively. Temperature, pressure, applied heating power; acentric factor and dipole moment were considered as input variables of the networks. The optimal parameters were obtained through the weights searching method. The average absolute relative deviations and correlation coefficient were 1.48 and 0.9998, respectively. This study shows therefore that the artificial neural network model represents an excellent alternative to estimate the thermal conductivity of different refrigerant systems with a good accuracy.

A general analysis of heterogeneous sources of waste heat at thermal power plants, taking into account the advanced world and domestic experience in creating high-power steam compression and absorption thermal transformers, has shown the possibility of significantly reducing heat losses by integrating absorption heat pumps and refrigerating machines of various designs and capacities into the thermal circuits of existing and projected thermal power plants. It is proposed to carry out a comprehensive optimization of the plants by creating intra-plant trigeneration systems. Taking into account the specific operating conditions of steam turbine condensers, cheaper multicomponent LiCl salt-based aqueous solutions, which are not inferior in efficiency to imported LiBr solutions with anticorrosive additives, are offered for the use as working bodies.

The paper presents the results of thermodynamic calculations and experimental studies on plasma processing of spent fuels and lubricants, which showed the prospects of using the plasma-chemical technology for processing liquid industrial wastes with the production of fuel gas and inert mineral material. The comparison of experimental and calculation results showed an acceptable agreement.

Explosive welding is a solid-state joining procedure that involves the propulsion of a flyer plate by the explosion of an explosive to produce welds of two or more similar or dissimilar materials. The development of molten intermetallic compounds at the interface degrades the mechanical properties of welded alloys. However, the employment of an interlayer in explosive welding significantly increases the kinetic energy dissipation and prevents the formation of molten intermetallic compounds at the interface, thereby increasing the bonding strength. Earlier researchers employed interlayers having different values of the thickness, yield strength, ductility, and density. The influence of the interlayer on the microstructure and mechanical properties of explosively welded similar and dissimilar alloys is thoroughly reviewed in this study. In addition, the significance of explosive welding in different environments, such as helium, underwater, and gelatin media, is also summarized. Correspondingly, future advancements in joining of materials through explosive welding are forecasted.

The mechanism of promoting the autoignition of rich methanol-air mixtures by small additions of hydrogen peroxide has been studied using the tracer method. It has been shown that with the addition of hydrogen peroxide, the oxidation of methanol with atmospheric oxygen begins with the formation of hydroxyl from peroxide, followed by its interaction with methanol to form CH₃O, CH₂OH and then HO₂ and H₂O₂. The branching factor for hydroxyl is higher with the addition of peroxide higher with than without the addition of peroxide.

When considering not only raw materials, but ecosystem functions of forests, the dynamics of forest stand indicators at all stages of growth is important. To regulate a high degree of fulfillment of ecosystem functions, the priority tasks are to increase the stability of stands and their productivity. The aim of the research is to study dynamics of growth and productivity of pine tree stands according to long-term observations data. The materials for the study were data of long-term observations due to the pine forest stands and plantations on permanent plots of the Forest Experimental Station of the Russian State Agrarian University - Moscow Timiryazev Agricultural Academy. Four main characteristics of the stock dynamics of pine stands have been identified, which requires the development of new approaches to its modeling. At the same time, the life cycle of a stand is not a monotonous process, as is customary, but a wave-like process of the dynamics of all main stand indicators, due to the different dependence of the influence of both internal (manifestations of self-regulation in stands and feedback loops) and external factors. The presence of several stages of dynamics can be reflected by empirical models, which include the sum of simple growth functions or nonmonotonic functions with one detection of the maximum or multiplicative-additive models of growth and correction functions. Generalized models of the dynamics of the stand basal areas and stocks of measurements that in late ages overcrowded stands have an advantage over rare ones. The nonmonotonic dynamics of stand yield and productivity indicators needs to be taken into account when substantiating the age of maturity and when designing thinning.

The results of long-term observations in pine tree stands of bilberry and sphagnum forest types are presented. The studies were carried out in the northern subzone taiga conditions of the European North-East of Russia. The method of observation on permanent sample plots was used (the period from 1967 to 2016). Pine tree stands develop on old logging areas (about 70 years ago) and after fire sites. Based on the results of observations carried out significant changes in the morphometric parameters of pine ( Pinus L.) trees and stands were established. In pine forests formed on logging areas, high values of the coefficients of variation of trees in terms of density and stock of stem wood (from 30 to 130 %) were revealed. Such high variation coefficients indicate their active formation. In post-pyrogenic naturally developing pine forests, the coefficients of variation of indicators vary from small (10 %) to high (40 %) values. In bilberry pine forests formed after logging, there is a tendency to reduce the density of trees, mainly caused by the loss of birch ( Betula L.) and aspen ( Populus tremula L.). Whereas, in sphagnum types pine forests, an active replenishment of forest stands with small pine trees from undergrowth was noted. It has been established that with an increase in the proportion of young generation of pine in the composition of forest stands, both a decrease in the average and current growth in stock, as well as a weakening of the vital state and an increase in damage to pine trees occur. During the observation period, the vital state of the most pine forest stands is characterized as «healthy status». In sphagnum types pine forests, the vital state of forest stands is somewhat weaker than in bilberry pine forests. This is due to the unfavorable conditions of their growth on waterlogged soils.

Studies were carried out in pine-birch stands with a second storey of spruce in the north-taiga forest region of Arkhangelsk Oblast (Obozerskoe forestry district), which are formed under the influence of thinning. It’s specified, that thinning at the age of 40 years for taiga zone is unreasonably late stage of formation in such stands. The best option is the formation of forest stands by thinning in three steps. Then, at the age of 40, carry out a second thinning operation, leaving 1000 trees per ha of pine and birch in the first storey, and 2000 trees per ha of spruce in the second storey. At the age of 60, carry out the third stage of thinning, leaving 500-600 pine trees per ha in the upper storey, and 1000 spruce trees in the lower storey. Numbering of pine in the structure is regulating within 90 %. Based on the results obtained in the course of the study, the silvicultural effect of thinning on permanent trial plots is the formation of a spruce storey, which in the future can replace the forest stand after the final felling of the first storey. When thinning in mixed pine forests completed, the attitude to undergrowth is important. Thinning can undoubtedly increase the productivity of forests. The results of the studies will serve as the basis for the subsequent development of recommendations for managing mixed pine-birch stands with a second storey of spruce.

In Russia, the intensive growth of areas naturally overgrown with such species as willow ( Salix L.), alder ( Alnus Mill.), pine ( Pinus L.), etc., increases the biodiversity of entire regions, but the contribution of these areas to the carbon balance and climate stabilization is mostly unknown. Especially critical in this regard is the situation with willow plantations, which was not included in the system of State accounting of the forest fund. Since the energy generated from willow plantations is CO₂ neutral, the use of this renewable and sustainable energy source has the potential to reduce global CO₂ emissions from fossil fuels. Willow phytomass can be used for the production of fuel in the form of chips, briquettes and pellets, and in some cases - for the production of bioethanol or wood gas. In addition to economic aspects, willow cultivation has a number of environmental advantages, such as the ability to accumulate toxins from polluted areas, improve landscaping and serve as hedges. To plan and manage forestry in willow plantations in the conditions of the North taiga subzone of Arkhangelsk Oblast and assess its contribution to the carbon balance, data on the biological productivity of willow trees and standards for assessing their phytomass are needed. The purpose of the study is to develop models and tables for assessing the structure and dynamics of the aboveground phytomass of the willow stands in the conditions of Arkhangelsk Oblast. To achieve it, the following tasks have been implemented: 52 sample plots have been established to assess aboveground phytomass of willows; regression models of the dependence of willow phytomass on the volume-forming inventory indicators of trees are constructed; the models obtained are combined with the yield table of willow stands and the table of age dynamics of willow phytomass is constructed according to site indices for the conditions of Arkhangelsk Oblast. A comparative analysis of the results obtained with data on the productivity of willows in Sweden showed that at the same age of stands, the stocks of aboveground phytomass of Swedish willow correspond to the stocks of phytomass of willows of Arkhangelsk Oblast at an average level between the I and II site productivity classes.

Urban green plantings have been recognized as an important component of the urban ecosystem. Inspecting the health of trees in settlements, in territories, near footpaths and highways is required regularly. In the city of Apatity, Murmansk Oblast, the state of the Siberian stone pine ( Pinus sibirica Du Tour) trees was studied, the presence of risk factors in the environment of the tree and damage that characterize the accident rate of the tree were determined. Visual inspection aims to identify symptoms of structural defects that may compromise the stability of the tree. Root zones, tree stems, crown base, skeletal branches, crown were assessed. The presence of hollows, cracks, signs of decomposition, fruiting bodies of fungi, damage and wounds, weak forks, dead branches were indicated. Among the examined trees, Siberian stone pine trees with a high risk of falling were not found. In trees in street row planting, a sparse crown is more often noted, damage to the butt zone, including mechanical damage. The root system of all examined trees functions in conditions of limited space. Trees in a linear planting along the road and pedestrian zones have more pronounced restrictions on the development of the root system. Stem damage occurs in all examined Siberian stone pine trees. Recommendations have been developed for regular monitoring, tree health pruning and other agrotechnical measures. The study carried out is of great practical importance. The results of the study can be used in the development of recommendations for the formation of a favorable ecological environment in the urbanized territories of the Arctic zone of Russia.

The features of the growth of spruce ( Picea A. Dietr.) trees of various state under the canopy of southern taiga oxalis birch forests ( Betuletum oxalidosum ) are considered. The studies were carried out at the North Forest Experimental Station of the Institute of Forest Science, Russian Academy of Sciences, where a system of permanent trial plots (PTP) was established to study the succession processes in birch forests. At one of the PTP, all spruce trees were cut down as models. Preliminary assessment of their condition (healthy, weakened) was carried out. The shape and foliation of the crown, its length along the height of the tree were taken as evaluation criteria. Growth analysis was performed for trees over 60 years old (40 healthy, 33 weakened). Tree growth was characterized by the dynamics of the following indicators: height, stem cross-sectional area at a height of 0.1 and 1.3 m, stem volume, form factor, shape factor. In the course of a retrospective analysis of the growth of trees, it was found that weakened trees, in terms of the value of the biometric characteristics of the stem, are significantly inferior to healthy ones already in the first 10 years of life. At the age of 60, the height and stem volume of healthy trees are 1.5 and 3.1, respectively, higher than the values of these indicators in weakened specimens. Regardless of the condition of the trees, the maximum average periodic growth in height is observed at 40 years, and the equality of the average and average periodic growths in weakened trees is observed 5 years earlier (55 years) than in healthy ones. The maximum average periodic growth in cross-sectional area and stem volume in weakened trees occurs 5-10 years earlier than in healthy ones. Weakened trees are characterized by more full-boled and less tapering stems. At the age of 60 years, the productivity of healthy trees under the canopy of birch forests corresponds to IV, and weakened ones - to V growth class. The prospects of spruce trees under the canopy of birch forests are best assessed when the spruce reaches the age of 40 years.

Forest area of the Far East reaches almost 50 % of the forest area of the Russian Federation. The share of the operational forest fund accounts for about 50 %, the rest are protective, protected, low-density, near-tundra and reserve forests. Most of the operational forests have been developed. The permissible volume of wood withdrawal is 92.0 million m³. Moreover, it is planned to harvest only 14 % by selective logging, the rest of the wood is planned to harvest by clear cuts. Care felling and forest health improving felling in the forests of the Far East are carried out in insignificant volumes. Timber harvesting during the creation of infrastructure facilities is organized mainly in subjects with a developed mining industry. The high diversity of forests and the differences in their growing conditions determined the need to allocate 12 special forest areas here, in 10 of which timber harvesting is carried out. Both continuous and selective logging methods are used. The main volume of logging take place on the Far Eastern taiga region and amounts 8.9 million m³, mainly by continuous logging. Selective logging of up to 3.5 million m³ of wood prevails in the Amur-Primorsky coniferous-deciduous area. In the Kamchatka taiga, Trans-Baikal forest-steppe and Altai-Sayan mountain-taiga forest areas, timber harvesting is carried out in insignificant volumes, only for the own needs of the population. Currently, due to the significant depletion of operational forests, the dynamics of timber harvesting in the Far Eastern Federal District tends to decrease.

Birch ( Betula L.) is a genus of approx. 60 species, subspecies or varieties with a wide distribution in the northern hemisphere. Understanding of systematics and evolution of this taxonomic group is of high practical importance, since most of the genus birch species are actively used in various industrial sectors and reforestation projects and are important forest tree species. The genus birch is considered to be one of the most complex among angiosperms. Taxonomy of birches has been revised several times, but systematic position of many representatives of the genus birch is being reconsidered today. Despite multiple comprehensive studies involving both morphological and molecular approaches a lot of unsolved issues remain in systematics and phylogeny of the genus birch. Main reasons for this include high variability of morphological characters, polyploidy, and intensive and widespread hybridization, which hampers identification of species. The purpose of the study is taxonomic analysis of the genus birch. Article discusses the features of birch introgressive hybridization, the origin of some species, summarizes the results of several molecular phylogenies based on various chloroplast and nuclear markers, and also lists birch representatives, whose taxonomic position is not confirmed by molecular genetic studies and requires additional study of natural populations using molecular markers. Various methods are used to determine the relationship between birch species: classical morphology analysis, chromosome number analysis and molecular genetic methods. One group of methods is not enough to clearly determine systematic position of some representatives of the genus birch. Therefore, the approach to the taxonomy and phylogeny of birches should be complex, using various modern methods complementing each other.

Comparative study was carried out by morphological, anatomical features of needles of four variations of the common juniper ( Juniperus communis L.). The plants belong to three ecological groups in relation to moisture - mesopsychrophytes, xeromesophytes and mesoxerophytes. Juniper variations choose different strategies for experiencing a lack of moisture. Mesopsychrophytes (a drought tolerance coefficient of less than 2) include variations of J. communis var . saxatilis and J. communis var. depressa and distinguished by small, blunt and thin needles, but large resin channels, the life form is a creeping shrub. Mesoxerophytes (drought resistance coefficient greater than 2.1) include, first of all, J. communis var. oblonga plants, have long, thick, sharp needles with two stomatal stripes, a large number of lining cells, large conductive bundles, developed conductive needle tissue, but small resin passages. These are usually tall shrubs or trees. Juniper variations of J. communis var. communis can be attributed to the group of xeromesophytes and by many features it occupies an intermediate position between J. communis var. saxatilis and J. communis var. oblonga . These plants, on the one hand, represent columnar shrubs and trees and have long sharp needles, small resin passages and, on the other, there are thin needles with as a rule, one stomatal strip and a small number of lining cells.

The issues of studying biological diversity, including at the intraspecific level, are among the most important in biology. The form diversity of woody plants is far from fully revealed. Most often, new forms are identified by crown habit, size and shape of leaf blades and their pubescence, size and color of flowers. Much less attention is paid to the color of the leaves. In the course of fieldwork in 2021, on the Kurtushibinsky Ridge, which is part of the Western Sayan system, in the protected zone of the Sayano-Shushensky State Natural Biosphere Reserve near the village of Bazaga, the authors found a small population of spiraea flexuous ( Spiraea flexuosa Fisch ex Cambess.) with bright, carmine-red leaves. Previously, no forms were noted in spiraea flexuous. However, for the closely related species S. сhamaedryfolia , which some authors previously considered a synonym for spiraea flexuous, 3 forms were described: f. crataegifolia Zhl., f. transiens Zhl. and f. stenophylla Zhl. They differed only in the shape and size of the leaf blades. Forms with leaves other than typical green have not been described before. The found form, being introduced into the arboretum of the Central Siberian Botanical Garden of the Siberian Branch of the Russian Academy of Sciences, retained its characteristics. In accordance with the Code of Botanical Nomenclature, she was given the name - Spiraea flexuosa Fisch ex Cambess., f. atropurpurea Karakulov et Shaulo. The red-leaved form of spiraea flexuousis highly decorative and can be successfully used in landscaping settlements in Siberia.

The analysis of the species richness and landscape positioning of terrestrial vertebrate animal communities in the territory of the potential impact of the reservoir of the planned Nizhneboguchanskaya Hydro Electric Power station (HEP) was carried out. The studies were conducted in the main animal habitats according to standard methods, from 2021 to 2022. The vertebrate fauna in the flooding zone and the potential impact of the projected reservoir of the Nizhneboguchanskaya HEP includes 250 species, including 56 species of mammals, 187 species of birds, 3 species of reptiles and 4 species of amphibians. There are eight main types of biotopes was identified: dark coniferous, light coniferous, mixed and small-leaved forests, wetland complexes, meadows and rocky outcrops. A comparative analysis of faunal richness was performed for each biotope type. The study showed that the highest species diversity is observed in forest habitat: from 126 to 155 species. Of these, the highest faunal diversity is inherent in communities of mixed forests, which is post-fire and after cutting long-derivatives of coniferous forests. Also, in different forest biogeocenoses, there is a high similarity in the species composition of terrestrial vertebrates. The most specific fauna compositions have rocky outcrops, wetlands and meadows, when compared with each other and, especially, with forest biocenoses. As a rule, these habitats are critical for the survival of a number of species, some of which are protected. The preservation of these habitats during the construction and operation of the Nizhneboguchanskaya HEP reservoir will require special attention to maintain the natural level of species diversity of terrestrial vertebrates.

The review is written for the book of Sergei Mikhailovich Bebiya «Forests of Abkhazia». Monograph. Sukhum: Academy, 2022. 589 p. (in Russian with English title, summary and contents).