For the first time in the world, a unique diamond has been discovered, with a smaller diamond freely moving in its cavity. The crystals were studied in detail by X-ray microtomography, which allowed us to build three-dimensional models of them, to establish in detail the morphological features of both the host and the prisoner minerals, and to determine the weight of each of them. On diametrically opposite surfaces of the host diamond, there are two through channels that lead to the cavity in which the internal diamondprisoner is located. The channels contain barite, and one of the channels is hermetically sealed with this mineral. At the entrance to the cavity, both channels are narrow and have a diameter of about 0.1 mm. The morphology of the internal walls of the cavity approximates the morphology of the surface of the internal diamond. According to the results of infrared spectroscopy, the diamond has a high content of structural nitrogen impurity 1,250 at. ppm. Integral volume mapping was performed using Raman confocal spectroscopy, which resulted in a layer-by-layer reconstruction of the internal structure of the diamond. Luminescence studies using a laser with a long excitation wave of 337 nm revealed a uniform pink-lilac glow in both diamonds.

The article presents the results of two paleontological experiments on Kotelny island, Novosibirsk Archipelago, conducted in 2019. During the survey work in the area between Kozhevena-Volosovich rivers, the skeletal remains of a woolly mammoth were found, approximately 30–40 % of the complete skeleton. The object lies in a small area that includes four baidjerakhs. Fragments of the skull, fragments of tusks, scapula, cervical, thoracic and lumbar vertebrae, a fragment of the sacrum, frgaments of ribs, fragments of the pelvis and bones of limbs were found at the location. At the moment, this is the most complete skeleton found on the Kotelny island. After the first comprehensive analysis of the bone material, traces of ancient human activity were identified. Traces of ancient tools were found on the skull, vertebrae, and ribs. But the most interesting thing is the tip of the «dart» remaining on the spine of the animal’s shoulder blade. Also, near the skeletal remains, tools of ancient man were found and identified, presumably a knife sharpener with traces of intense use, and something like a «spatula». The results of radiocarbon analysis correspond to the kargian epoch of the late neo-Pleistocene. The climatic conditions of that time were somewhat better than modern ones, although they differed by more arid and hot summers. This finding expands the territory of ancient human activity in the late neo-Pleistocene.

The article presents the data on the new findings of the remains of a woolly mammoth (Mammuthus primigenius Blumenbach, 1799) found in the Olekminsky district of Yakutia. In the summer of 2018. parts of the skeletons of woolly mammoths were found in the area of Legentei Oyogoso and on the banks of the Dapparay Creek. Findings of Late Pleistocene animals in the south-east of Yakutia are quite rare, and for this reason the Dapparay mammoths are of great interest to science. Measurements of thirty two bones belonging to three mammoths were carried out. The morphometric characteristics of the Dapparay mammoths were compared with the measurements of the bones of the Berezovsky, Taimyr and Gydan mammoths. Based on the results of comparative studies of morphometric indicators, it was concluded that the mammoths that lived in southern Yakutia did not have significant differences from their northern relatives. This may indicate more or less uniform climatic conditions in their habitat zone.

The article examines the geocrylogical studies of the southern part of Western Yakutia, the territory of which is adjacent to the area of well-developed diamond deposits of Yakutia. The geocrylogical conditions of diamond deposits have been studied in detail. In most fields, the presence of a deep cryolithozone with a non-stationary temperature field was revealed. Cryolithozone thickness drastically decreases in the southern direction and passes into island and intermittent cryolithozone. In this regard, the transition zone requires additional geocrylogical study. In addition, there is currently intensive development of oil and gas fields in the south of Western Yakutia. Most of the hydrocarbon transportation and processing facilities are located at the territory representing the zone of island and intermittent spread of permafrost rocks. While the main task of engineering and geocryological research in the continuous permafrost zone is to study the morphology and temperature of cryolithozone, in the areas under study the problem of identifying ‘islands’ of permafrost rocks and assessing their cryogenic structure becomes particularly relevant.

The experience of inwashed soil development under the conditions of permafrost is considered for various engineering structures: the foundations of gas-oil, industrial and civil facilities, soil hydraulic facilities, roads, etc. Particular attention is paid to the technology of construction of the foundation of inwashed soil on the low floodplain of the Lena river for the residential complex of the Yakutsk city (quarters No. 202 and 203). The results of studies into the dynamics of the geocryological conditions over this territory during the long-term operation of buildings and engineering structures are presented. It was revealed that in the major part of the territory of quarter No. 202 in Yakutsk, which was constructed in the 1980–90s according to the 1st principle, at present the ground has a positive temperature at a depth of 10 m and deeper. At the territory of quarter No. 203,, suprapermafrost aquiferous taliks, were formed during hydromechanical works in the 1990s, and they still exist everywhere after 30 years. The factors that contribute to the preservation of suprapermafrost taliks in the body and base of the inwashed soil are considered. The main factors determining the formation of the soil temperature field include distinct thermophysical properties of dry inwashed sands in the upper part of the section and the hydrogeological conditions of the territory. The features and prospects of inwashed soil exploitation as the structure foundations and the principles of construction on them are analyzed. To control and develop robust recommendations for ensuring the sustainability of structures, it is necessary to organize comprehensive geocryological monitoring, including ecological aspects of the interaction between technogenic systems and the environment.

The article discusses the origin of relict steppe sites found in some regions of Yakutia, mainly in the central and northeastern parts, as well as their distribution in the Late Pleistocene as a resource niche for a mammoth megafaunistic complex. It was shown that the true steppes existed on the territory of Yakutia in the Pliocene and Early Pleistocene. Xerophytic plant communities of the Middle Pleistocene genetic related to mountain-steppe associations. In the Late Pleistocene, cryoxerophytic phytocenoses did not have trans-Bering links, but were more widespread than at present.
The wide distribution of cryoxerophytic barren communities in the Late Pleistocene was due to extreme cryoaridity of the climate and low rainfall, especially in winter, which led to soil surface cooling. Despite the extremely low productivity, cryoxerophytic wastelands gave an ecological niche to a rather large ungulate saiga, which for a long time served as an argument in paleobotanical reconstructions for the distribution of steppes in Late Pleistocene.
In the Late Pleistocene, modern relict steppe plots occupied a subordinate position in the vegetation cover of Yakutia, which is still observed today.

The article presents the results of original observations during the years 2003 to 2019, analysis of literature data, archival and questionnaire information on the representatives of the Falconiformes order inhabiting or seen in the Middle Lena valley and adjacent territories. At present, 16 species are regularly found in the study area. Among them, 13 species are nesting here, 3 are possible nesters, and 2 species occur during seasonal migrations and shifts. The paper gives a relative estimate of the abundance in a long-term retrospective of Peregrine falcon and the current states for populations of other daytime birds of prey in the region. It is noted that until the middle of the 20th century, many representatives of the order were common species of the local avifauna at the Middle Lena valley, and a noticeable reduction of their number began in the 60s of the past century. At present, from all the daytime birds of prey in the study area, only Kites and Kestrels are widespread, common and locally numerous, and the rest are not numerous or rare. In the recent decades, most of the Middle Lena territory has undergone an intensive transformation of natural communities, and the species listed in the Red Book react most acutely to this process, like Osprey, Golden eagle and White-tailed eagle known for their intolerance to changes and reducion in the areas of their habitats.

For the purpose of monitoring the state of forest ecosystems, it is most effective to use the capabilities of remote sensing methods. Fragments of 0.819 km2 (scale 1: 3200) with the dominance of Scots pine (Pinus sylvestris L.) and Gmelin larch (Larix gmelinii Rupr.) were identified on DigitalGlobe multispectral satellite images of the territory of the Olekminsky State Nature Reserve. Then, the polygons were saved at four levels of detail – 4.16.64.256 with scales of 1: 1600.1: 800, 1: 400, 1: 200. When decoding, an uncontrolled classification of the fragment and polygons was carried out using the ISODATA (Iterative Self-Organizing Data Analysis Technigue) method for 2,4,10 classes. According to the results of classification into 2 classes, the relationship between the forest cover index and the number of trees marked on the landfills is shown. The distribution curves for forest cover index values were constructed for polygons at level 4 of detail. The nature of the curves is close to the normal distribution. According to the classification results for grades 4 and 10, statistical processing was carried out with the calculation of the indicators of the difference and similarity of the polygons – the dispersion of the general aggregate and the Fisher test (F-test). The most similar pairs of polygons at different levels of detail are highlighted. The results of changes in the dispersion and the F-test at different levels of detail are considered.

The paper presents results of experimental and theoretical studies on fracture of gypsum plates containing a circular hole and subjected to non-uniformly distributed compression. The tested specimens were made of high-strength gypsum, and from gypsum plaster. The specimens of high-strength gypsum were broken in the brittle manner, while the specimens of gypsum plaster demonstrated quasi-brittle fracture. To calculate the critical load, amodified nonlocal fracture criterion is proposed, which is the development of the average stress criterion, and which contains a complex parameter that characterizes the size of the fracture process zone and accounts not only for the material structure, but also for the plastic properties of the material, geometry of the specimen, and its loading conditions. The calculation results are in good agreement with the experimental data. In addition, the application of the modified nonlocal criterion makes it possible to explain the change in the character of fracture from brittle to ductile with an increase in the size of the hole, observed in the experiment. The results obtained are of great practical significance for assessment on the strength of materials and structures with stress concentration.

This paper presents the results of the investigation of polytetrafluoroethylene (PTFE) modification with mineral silicate (sericite) and its effect on the physicomechanical, tribotechnical properties and structural parameters. Two methods were used to develop a polymer composite material (PCM): mechanical and thermal activation of natural silicate before mixing with the polymer. It was shown that PTFE filled with thermally activated sericite is characterized by higher physicomechanical and tribotechnical parameters in comparison with the composites containing mechanically activated filler. By means of X-ray diffraction analysis, it was found that the modification of PTFE with mechanically activated sericite leads to an increase in the degree of crystallinity of PCM, and the use of thermally activated filler is accompanied by a decrease in crystallinity. A correlation between the degree of crystallinity and the average crystallite size of the composites was revealed, depending on the filler content. IR spectroscopy established the occurrence of tribochemical reactions during the frictional contact of the composites with the counterbody, contributing to the formation of a surface layer localizing shear deformations and protecting the material from wear.

The results of studies into the physicomechanical properties of polymeric materials based on polytetrafluoroethylene and its composites with carbon fibres of the UVIS-AK-P brand are presented. The technology of these composites involves the plastic deformation of polymer materials by compression, accompanied by the change of thickness at a constant width of the workpiece. It was found that the use of this technology allows not only to increase the tensile strength of PTFE by a factor of 2.7–3.3 with a compression ratio of 3–4.3, but also to reduce its creep deformation by a factor of 22–29, compared to the original polymer. The proposed technology is also tested on a PTFE composite containing a carbon fiber material of the UVIS-AK-P brand in the amount of 5 mass %. It is shown that in this case, the strength of the composite increases by a factor of 3, and the creep deformation decreases by a factor of 8.3, compared to the original composite, which was not subjected to plastic deformation. The proposed technology for producing fluoroplast composites allows expanding the scope of their application, and the developed materials can be used in various friction points, especially for loading schemes with high tensile loads.