The influence of modification by superdispersed powders on the lead-tin-base bronze structure

The paper presents data on the influence of additives of the pre-treated aluminium oxide powder on the structure of cast lead-tin-based bronzes. Different quantities of the modifier, based on the superdispersed aluminum oxide powder, were added to the bronze melt. The studies have shown that addition of a small amount of aluminum oxide powder (0.07... 0.25 %) allows modifying the micro structure of the obtained castings. This modification includes grain refinement, reduction of the matrix dendrites size of tin solid solution in copper, as well as formation of spherical inclusions of the low-melting phase - lead. In this case, the addition of such modifier influences weakly the morphology and the quantity of solid eutectoid inclusions based on electron compound Cu[31] Sn[8]

The balance of elements in the system “Luvic Chernozems – agricultural plants” on the Plavsk upland (Tula region of Russia)

To assess the transfer of macro (K, P, S, Mg, Ca, as well as Si, Na, Fe, Al, Mn and Ti) and microelements (Zn, Ba, Cu, Sr, Mo, as well as As, Zr, Pb, Co, Ni, V and Cr) from Luvic Chernozems (Aric, Loamic, Pachic) into agricultural plants, we studied the inventories of chemical elements in three agrocenoses (wheat, soybean, Galega orientalis Lam. and Bromopsis inermis Leyss grass mixtures) from the Plavsk upland (Tula Region). This territory is subjected to intensive industrial and agricultural impacts: it is 40 km away from the town of Shchekino with a nitrogen fertilizer plant and a thermal power plant, 60 km away from Tula with large metallurgical enterprises, 70 km away from the town of Novomoskovsk with several chemical enterprises and state district power plant. In soils, the total content of elements was determined by the X-ray fluorescence spectrometry. The elemental composition of plants after autoclave decomposition with a mixture of concentrated nitric acid and hydrogen peroxide and the content of the bioavailable fraction (extracted by an ammonium acetate buffer with pH 4.8) of elements in soil were estimated by the atomic emission spectrometry with inductively coupled plasma. In topsoil (a 10-cm layer), maximal inventories are typical for total Si (40 ± 4 kg/m2), Al (7.0 ± 0.8 kg/m2) and Fe (3.4 ± 0.3 kg/m2) and for bioavailable Ca (570 ± 48 g/m2), Mg (43 ± 4 g/m2), K (22 ± 6 g/m2). In plants, the main inventories (g/m2) of K, P, S, Mg, Si, Mn, Zn, Ba, Cu, Mo occur in the above ground phytomass. The most effectively plants assimilate bioavailable fractions of K, P, Ti, Mo, As, Zr, V. Based on the resource method for soil quality assessment, the studied Chernozems are characterized by a low level of Ni contamination, a moderate supply of bioavailable K with a lack of bioavailable P

Азотсодержащие вещества в снеге районов падения ступеней ракеты-носителя «Протон» в 2009–2019 гг.

The article presents analysis of the snow pollution caused by flights of the Proton launch vehicles launched from the Baikonur cosmodrome in 2009–2019. Data on 1477 snow samples collected in areas in Central Kazakhstan, south­east of Western Siberia, and north­east of the Altai are summarized to assess the pollution. In the uninhabited areas in Central Kazakhstan, where rocket fuel is spilled, pollution of snow was detected at 18 fall sites at a distance of up to 10 m from the fragments of the stages. The background value of pH is estimated as 6.6±0.9. The following nitrogen-­containing compounds (mg/l) were found in snow taken in the unpolluted territories of Central Kazakhstan: NO3­ (2.3±3.4), NH4+ (0.75±0.98) and to a lesser extent NO2– (0.015±0.019); asymmetric dimethylhydrazine and nitrosodimethylamine were not detected. The chemical composition of snow in the fall areas of the second stage of the Proton launch vehicle is in a good agreement with the background level of nitrogen­-containing substances of natural origin. There were no traces of the rocket fuel. Thus, in the snow on the Ketsko­Tym plain (south­east of Western Siberia) and north­east of Altai, the background content of nitrogen-­containing substances is equal, respectively (mg/l): NO3– (0.36±0.28 and 0.47±0.59); NH4+ (< 0.05 and 0.20±0.27); NO2– (0.048±0.016 and 0.027±0.073), which is determined by regional features and distance from sources of nitrogen­-containing substances. The data obtained allow us to conclude that the areas of the rocket falls on the above territories are not an environmental hazard to the environment by the concentration of nitrogen-­containing substances in the snow.Обобщены данные по 1477 пробам снега из районов падения ступеней ракеты-носителя «Протон» в Центральном Казахстане, на юго-востоке Западной Сибири и северо-востоке Алтая. В безлюдных территориях Центрального Казахстана, куда попадает ракетное топливо, достоверное загрязнение снега установлено на расстоянии не более 10 м от фрагментов падения первой ступени. Химический состав снега районов падения второй ступени (юго-восток Западной Сибири и северо-восток Алтая) отражает фоновые уровни азотсодержащих соединений природного происхождения и показывает отсутствие компонентов ракетного топлива. Очевидно, что районы падения и первой, и второй ступеней ракет-носителей «Протон», запускаемых с космодрома Байконур, не представляют собой зоны экологического бедствия

Insights into substrate stabilization from snapshots of the peptidyl transferase center of the intact 70S ribosome

Protein synthesis is catalyzed in the peptidyl transferase center (PTC), located in the large (50S) subunit of the ribosome. No high-resolution structure of the intact ribosome has contained a complete active site including both A- and P-site tRNAs. In addition, although past structures of the 50S subunit have found no ordered proteins at the PTC, biochemical evidence suggests that specific proteins are capable of interacting with the 3′ ends of tRNA ligands. Here we present structures, at 3.6-Å and 3.5-Å resolution respectively, of the 70S ribosome in complex with A- and P-site tRNAs that mimic pre- and post-peptidyl-transfer states. These structures demonstrate that the PTC is very similar between the 50S subunit and the intact ribosome. They also reveal interactions between the ribosomal proteins L16 and L27 and the tRNA substrates, helping to elucidate the role of these proteins in peptidyl transfer

THE SPATIAL DIFFERENTIATION OF SOIL SALINITY AT THE YOUNG SALINE COASTAL PLAIN OF THE CASPIAN REGION

The study is focused on the pattern of soil salinity at the young loamy coastal plains of the Caspian Sea in Russia and Iran which were released from water less than 300 years ago. At two key sites of 45×30 m (Russia) and 25×20 m (Iran), the soil sampling with 1 to 5 m grid was performed to the depth of 1 m. The electrical conductivity (1 : 2.5) was measured in soil samples and soil sa-linity maps were compiled. Soils are represented by solonchaks with 2–3% of salts in the top layer or highly saline soils partly leached in the upper 5–10 cm. The ground water table is shallow (2–2.5 m). The studied sites are different in terms of climate, microtopography, and vegetation cover but spatial differentiation of soil salinity is quite similar what is evidenced from the similar distributions (mean values and variance) of electrical conductivity in almost all studied depths. The redistribution of salts is mainly observed in the upper 50 cm with the maximal manifestation in the upper 5 cm