A procedure for the synthesis of the new ditopic ligand combining in the structure 1- and 5-substituted tetrazolyl cycles, 5-(2-(1
H
-tetrazol-1-yl)phenyl)-1
H
-tetrazole (HL), is developed. The ...coordination compounds of Co(II) and Cu(II) halides Co(HL)
2
Cl
2
, Cu(HL)
2
Cl
2
, Cu(HL)
2
Br
2
, and CuL
2
(H
2
O)
n
based on ligand HL are synthesized. The complexes are studied by elemental analysis, diffuse reflectance spectroscopy, IR spectroscopy, X-ray diffraction (XRD), and static magnetic susceptibility. The crystal structure of the molecular coordination polymer CuL
2
(H
2
O)
n
is determined by XRD (CIF file CCDC no. 2127210). The temperature and field dependences of the magnetization show that the magnetic properties of the synthesized Cu(II) complexes are due to exchange interactions in one-dimensional chains of the copper ions (
S
= 1/2). For complex Cu(HL)
2
Br
2
, the parameters are shifted toward the enhancement of the antiferromagnetic interaction compared to the analog containing the chloride ion.
An energy criterion is proposed for the level of agglomeration (coalescence) of nanowires fixed at the base on a rigid substrate and immersed in a continuous medium (air, liquid), which excludes ...capillary phenomena. This criterion, based on the competition between the elastic energy of a bent nanowire and its surface formation energy, can also be applied to the attachment of nanowires to a surface and (in a modified form) to the coalescence of details of micro- and nanomachines. Nanowires for surface-enhanced Raman scattering, obtained by template synthesis based on track membranes, with subsequent removal of polymer, are considered as a specific example.
Description of modern pyroelectric technologies is presented in this article. Various schemes for generating X-ray radiation are presented. The possibility of controlling charged particle beams by ...means of a pyroelectric deflector is demonstrated. The prospects for the development of pyroelectric technologies and their application are discussed.
—
The power unit availability factor depends in many respects on the reliability of the steam turbine’s last-stage rotor blades. In the course of operation, rotor blades experience static and ...vibration loads caused by steam flow, due to which they are often damaged as a result of fatigue stresses. Relatively long last-stage rotor blades of steam turbines are components that especially often suffer from damage. Emergency shutdowns of a turbine caused by blade system faults account for one quarter of their total number, and the time of power unit emergency outages resulting from blade breakdowns accounts for more than half the total time of their being in the outage state. In manufacturing high-capacity steam turbines, special attention is paid to ensuring vibration reliability of last-stage rotor blades. The article describes a technology applied to ensure the dynamic vibration reliability of the last-stage rotor blades of the steam turbines produced by Leningrad Metal Works (LMZ) at the stage of manufacturing them with the use of vibration tests carried out on a dedicated bench (the Campbell machine) in the rotor speed range in which resonances excited at engine orders from three to ten are observed. The article also presents the Campbell diagram of the last-stage rotor blade of a high-capacity steam turbine with the maximal stresses in the rotor blade that occur during resonances excited at engine orders from two to six and also the results from a comparison between the predicted and experimental distributions of relative stresses at the leading and trailing edges over the blade length during disc vibration at engine order four.
The results of experimental studies on the generation of x-rays when operating a piezoelectric kitchen lighter in a vacuum are presented. For the first time, a new method for increasing the intensity ...of x-ray radiation in the piezoelectric effect in a high vacuum through the use of an additional electron emitter is proposed and demonstrated. The maximum energy of x-ray bremsstrahlung reaches 14 keV. This means that electrons are accelerated in vacuum in the field of a piezoelectric ceramic to energy of at least 14 keV.
Long-term variations in the water balance were analyzed in the basins of 20 largest tributaries of the Baikal. The values of river runoff were derived from actual data on the period from 1976 to ...2019, and those of evaporation, precipitation, and potential evaporation, from ERA5-Land reanalysis since 1976 to 2020. Data were obtained to show an increase in the potential evaporation in all analyzed drainage basins by values from 0.39 to 0.62% per year since 1976 to 2020. A moderate or statistically insignificant decrease is typical of precipitation (0.25 to 0.59% per year) and water discharges, mostly due to a decrease in the summer runoff at a rate of 5.6%/10 years. The possible role of changes in vegetation cover in these processes was studied by evaluating NDVI parameter in 2019 compared with 2002 by data of space surveys MOD13A3 and MYD13A3 with MODIS spectroradiometer of Terra and Aqua satellites. A conclusion was made about the key role of precipitation in the decrease in the maximal runoff in Lake Baikal basin.
To assess the state of the regional vocational education system, the authors developed an open five-level assessment model, on the basis of which a set of studies was performed, including cluster and ...factor analysis. Based on the use of the main components method, a methodology for reducing the dimension of an array of indicators for subsequent clustering of regions is proposed.
For the first time, the joint use of regression analysis and the method of main components for obtaining a stable set of indicators for assessing the regional vocational education system was proposed and tested.
A relationship was found between the stability of the assessment model of the vocational education system and the directions of action of indicators, both within one indicator group and in different indicator groups.
The morphology and phase composition of the surface of La
3
Ga
5
SiO
14
(langasite) crystals at annealing in a temperature range 1000–1200°C have been studied using electron and atomic force ...microscopy. It has been shown that trigonal lanthanum oxide (La
2
O
3
) crystals with sizes to 3–4 μm, as well as a microstructure with sizes to 50 μm with gallium excess, with the approximate composition of 15 mol % La
2
O
3
, 65 mol % Ga
2
O
3
, and 20 mol % SiO
2
are formed on the surface of langasite crystals annealed in air at temperatures above 1100°C. Possible reasons for thermal destruction of the compound can be a significant rearrangement of the disordered crystal structure of langasite caused by the interaction with air oxygen and under the intense surface diffusion of atoms of the crystal, as well as the incongruent character of melting of the La
3
Ga
5
SiO
14
compound. The revealed thermal destruction of the surface of langasite crystals should be taken into account when using this material to fabricate piezoelectric elements for operation at high temperatures.
A study of the kinetics of ethanol conversion in the presence of Zr-containing zeolites BEA doped with palladium particles has revealed the order of formation of the main reaction products. It has ...been shown that the primary processes are ethanol dehydrogenation to acetaldehyde on Pd sites and ethanol dehydration to diethyl ether on the acid sites of the catalyst. After that, acetaldehyde undergoes the aldol–croton condensation reaction to form crotonal, which is hydrogenated to butanol on the metal sites. Butanol, in turn, is dehydrated into butenes, which undergo hydrogenation to butane. The presence of hydrogen in the gas phase leads to the displacement of ethanol from the metal surface and prevents the formation of surface carbonates and acetates. It has been found that hydrogen significantly accelerates ethanol dehydration owing to a decrease in the activation energy, which can be attributed to hydrogen spillover to the zeolite. The addition of water inhibits all acid-catalyzed reactions owing to competitive adsorption on acid sites and thereby decreases the butanol yield and the ethanol conversion.
The effect of imidazole, histamine, histidine, and their nitro derivatives on the radiation-induced transformations of glycero-1-phosphate and ethanol in deaerated aqueous solutions at pH 7 has been ...studied It has been found that the test substances in equimolar concentrations to glycero-1-phosphate inhibit the radiation-induced dephosphorylation by scavenging the radical products of water radiolysis. At an additive-to-substrate ratio of 1 : 100, the nitro derivatives of histidine and metronidazole efficiently inhibit the radiation-induced dephosphorylation of glycero-1-phosphate due to the interaction with its carbon-centered radicals with constants of (3.1–5.1) × 10
9
L mol
–1
s
–1
. Using the radiolysis of a 1 M aqueous solution of ethanol, it was demonstrated that 5-nitroimidazoles quantitatively oxidize α-hydroxyethyl radicals; this manifested itself in the absence of 2,3-butanediol among the radiolysis products and a ~20-fold increase in the yield of acetaldehyde, as compared to that in a control experiment. Thus, metronidazole and the nitro derivatives of histidine are capable of suppressing the radiation-induced dephosphorylation of glycero-1-phosphate and, probably, glycerophospholipids due to the oxidation of their α-hydroxylcontaining carbon-centered radicals.
PDF
