Статьи

Представлены результаты исследования условий синтеза графена и систем на его основе без использования подложек при конверсии жидких и газообразных углерод-содержащих материалов в гелиевой, азотной или аргоновой плазме, генерируемой электродуговым плазмотроном, при пониженном давлении. С помощью комплекса физико-химических методов установлено, что при синтезе в объеме морфология графена имеет вид смятой бумаги. При изменении геометрии проточной части реактора без использования подложек формируется структура гидрированного графена. Использование азотной плазмы позволяет получить графен, допированный атомами азота или меди. При добавлении спиртов в плазму аргона или гелия происходит синтез термически стабильного окисленного графена. Сделан вывод о возможности применения плазменных условий для одноступенчатого синтеза графеновых материалов.

Эта работа посвящена применению ансамблевых и нейросетевых методов машинного обучения, в частности методов CatBoost и LightGBM и сверточных нейронных сетей, для прогнозирования ВВП. В исследовании используется база винтажных данных, что позволяет выявить влияние пересмотров статистической информации на точность моделей. Полученные нами результаты показывают, что комбинации нейросетевых методов сохраняют прогнозное преимущество по сравнению с эталонными моделями – авторегрессией первого порядка, динамической факторной моделью и байесовской векторной авторегрессией – на панели стран, в том числе в периоды, включающие пандемический кризис, на предварительных и пересмотренных данных. Согласно эконометрическому тесту на доверительное множество моделей, к числу наиболее точных методов прогнозирования ВВП относятся сверточные и рекуррентные нейронные сети. Пересмотры статистических данных приводят к росту среднеквадратической ошибки эталонных моделей, ансамблевых и нейросетевых методов машинного обучения.

Objective: to evaluate the immediate and long-term outcomes of revision total knee arthroplasty using porous metaphyseal sleeves and cones.

Materials and Methods. The study included 134 patients who underwent revision total knee arthroplasty. The patients were distributed among two groups based on the type of metaphyseal fixator: sleeves (Group I, n=97 patients) and cones (Group II, n=37 patients). Surgical outcomes were assessed upon discharge from the hospital (after the hospital stay of 7-12 days), as well as after 6, 12 and 24 months after surgery. The survival rate of endoprostheses was analyzed using the Kaplan–Meier method. A revision with total replacement of the endoprosthesis or its components was considered a critical event.

Results. The analysis of the survival rate of endoprostheses in the form of various metaphyseal fixators showed that the groups of sleeves and cones did not differ statistically significantly as suggested by the logrank test (Mantel–Cox): p=0.108. Conclusion. The midterm follow-up revealed no difference in clinical, functional, or radiological outcomes of revision total knee arthroplasty performed for types 2A, 2B, and 3 of bone defect replacement (sensu Anderson Orthopaedic Research Institute classification) using trabecular metal metaphyseal cones vs. sleeves.

Objective: to evaluate the activity of oxidative stress in rats with stepwise incomplete cerebral ischemia (SICI). Material and methods. Experiments were performed on 24 male outbred rats weighing 260±20 g, allocated into 3 subgroups (6 animals in each) based on time of ligation of both common carotid arteries (CCA). The control group comprised of sham-operated rats of the same sex and similar weights (n=6). To identify the pro-oxidant–antioxidant state of the brain based on its homogenates, the activity of lipid peroxidation processes, the content of thiobarbituric acid reactive substances (TBARS), the concentration of reduced glutathione (GSH), total thiol groups (TSH), and the activity of glutathione peroxidase were determined.

Results. SICI with ligation interval of both CCAs of 1 day and 3 days led to a significant decrease in the total SH groups of proteins and glutathione by 30% (p=0.038) and 46% (p=0.044), respectively, TBARS concentration by 29% (p=0.038) and 31% (p=0.043), respectively. SICI with the maximum interval between CCA ligations was manifested by less pronounced changes in the pro-oxidant–antioxidant state of the brain.

Conclusion. In SICI with ligation of both CCAs 7 days apart, at which histological changes were the least pronounced, changes in the pro-oxidant–antioxidant balance were insignificant. The most pronounced disorders of the pro-oxidant–antioxidant balance in the brain were observed in the subgroup with the minimum interval between CCA ligations, which implied the highest activity of oxidative stress.

The article examines the crusades and integration processes in Europe in the period of XI–XIII centuries on the basis of Russian and foreign historiography.

In conclusion, the author notes that the crusades, which initially were the “military-integrative expansion” of the Europeans, increasingly turned into a purely aggressive campaign, gradually losing the spiritual basis under the leadership of the papacy, which began the period of decline. Contemporaries of the crusades were skeptical about these military-religious expeditions. The Reformation of the XVI century put an end to the Christian republic of scientists, which Erasmus of Rotterdam dreamt of. There came a time when, along with the religious integration, purely political unions were also being formed, joined by the opponents who were difficult to be imagined together (for example Francis I and the head of the “true believers”, the Turkish sultan).

Purpose. Development of regional satellite algorithms requires the information on bio-optical properties of a particular water area. The present study is aimed at comparative analysis of bio-optical properties of optically complex waters differing in their trophic status.

Methods and Results. The study combined the results of measuring the spectral bio-optical properties in the waters of the Black, Azov, Barents and Norwegian seas, the Arctic and Southern oceans (Atlantic sector) and Baikal and Teletskoye lakes. Spectral coefficients of light absorption by phytoplankton, non-algal particles and colored dissolved organic matter were measured in accordance with the International Ocean Colour Coordinating Group Protocols. The study areas included the waters with trophic levels from the oligotrophic to the eutrophic ones (the chlorophyll a concentrations in the surface layers varied from 0.066 to 24 mg⋅m−3) and with high heterogeneity in their bio-optical properties: the total non-water light absorption at the wavelength of 438 nm varied from 0.021 to 0.97 m−1.

Conclusions. In all the regions, a high (within an order of magnitude or higher) spatial variability in the values of light absorption coefficients by all the optically active components and their ratios was noted. This fact indicates the optical complexity of waters in each of the regions under study. The regional specificity of parameterization coefficients for light absorption by phytoplankton, non-algal particles and colored dissolved organic matter was shown. The revealed parameterization coefficients for light absorption by the optically active environment components can be used to develop regional satellite algorithms for assessing water quality and productivity indicators. Based on the empirically revealed dependencies, the following additional indicators of water quality were proposed: the euphotic zone depth and the spectral characteristics of downwelling irradiance which can be retrieved based on remote sensing data.

Purpose. The aim of the study is to analyze the features of mean long-term structure and intra-annual variability of the characteristics of temperature fronts on the ocean surface in the Patagonian shelf region.

Methods and Results. Mean daily values of the ocean surface temperature from the NOAA OI SST data and the geostrophic velocity components on the surface at the nodes of a 0.25° regular grid from the CMEMS reanalysis for 1993–2020 were used. It is shown that at the western periphery of a large-scale cyclonic meander formed by the currents in the Patagonian shelf region (south of 45°S), three branches of the Subantarctic Front are traced; they correspond to theWest Falkland Current and to two jets of the East Falkland Current. North of 45°S, where one Falkland Current jet is observed, one branch of the Subantarctic Front is identified. On the eastern periphery of the meander, the front corresponding to the common stream of the Brazil Current and the Falkland Return Current is revealed. Besides, south of 40°S, a separate branch of the Subantarctic Front corresponding to one more recirculation of the Falkland Current is observed. It is shown that at the meander western periphery, the branches of the Subantarctic Front are most intensified in February – March, at its eastern periphery – in March – April, and at the meander northern peak (in the zone of the Brazil – Falkland Confluence) – in April – May and November.

Conclusions. It is found that on the western periphery of the cyclonic meander, south of 45°S, the main branch of the Subantarctic Front approximately follows the 900–1000 m isobaths, north of 45°S – the 150–170 m isobaths, and closer to the Brazil – Falkland Confluence – the 50–60 m isobaths. At the meander eastern periphery, north of 40°S, the main branch of the front is very close to the 800–1000 m isobaths, south of 40°S – to the 1000–2500 m isobaths. It has been established that the differences between the seasonal cycles of intensity of the Subantarctic Front branches are related to the dissimilar warming and cooling rates of surface waters separated by these branches.

In this paper, we consider the Fredholm integral equations of the second kind and construct a new iterative scheme associated to the Nyström method, which was elaborated by Atkinson to approximate the solution over a large interval. Primarily, we demonstrate the inability to generalize the Atkinson iterative methods. Then, we describe our modified generalization in detail and discuss its advantages such as convergence of the iterative solution to the exact solution in the sense norm of the Banach space С0[a,b]. Finally, we give a numerical examples to illustrate the accuracy and reliability of our generalization.

В нашей статье отмечены аспекты новой коронавирусной инфекции в аспекте медицинской биологии на основе литературных источников.