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241.
Numerical modeling data on evolution of the stress-strain state of a rock mass containing a karst cavity are reported.  相似文献   
242.
The feasibility of the labeling procedure involving thermal activation (TA) of tritium was examined with the substrates that are commonly labeled by solid-phase catalytic hydrogenation (SCH) with tritium. Comparative characteristics of SCH and TA as procedures for tritium labeling of sugars and diazines were obtained. These two methods ensure comparable rates of tritium incorporation into purine and pyrimidine bases. The SCH allows preparation of tritium-labeled compounds with the maximum possible molar radioactivity. The molar radioactivity of the same compounds labeled using TA did not exceed 37 TBq mol−1, because only a small fraction of the substrate could react with atomic tritium. Longer reaction times and increased amounts of tritium taken into the reaction resulted in stronger degradation of the substrates. On the assumption that the reactive tritium atoms penetrate into the target to a depth of 0.5 nm, the actual specific radioactivity of the labeled compound in the zone accessible for atomic tritium reaches 0.2–2 PBq mol−1. Ways are suggested to increase the molar radioactivity of compounds labeled using thermal activation of tritium.__________Translated from Radiokhimiya, Vol. 47, No. 3, 2005, pp. 284–288.Original Russian Text Copyright © 2005 by Sidorov, Badun, Baitova, Baitov, Platoshina, Myasoedov, Fedoseev.  相似文献   
243.
The equilibrium of the reaction U(VI) + 2Ce(III) ⇄ U(IV) + 2Ce(IV) in the presence of unsalurated heleropoly compounds K10P2W17O61 and K8SiW11O39 in 0.01–1.0 M HClO4 solutions (ionic strength 1) was studied. The potential of the Ce(IV)/Ce(III) couple in K8SiW11O39 solutions was measured, from which the overall stability constants β2IV of the complexes UIV(SiW11O39)212−, equal to 1023.8 and 1019.8 in 0.1 M HClO4 + 0.9 M NaClO4 and in 1.0 M HClO4, respectively, were calculated. Under the same conditions, for the complex UIV(P2W17O61)216− β2IV = 1023.2 and 1018.5 (the latter value was obtained by extrapolation or data for 0.1 M HClO4 + 0.9 M NaClO4 solution). Original Russian Text ? V.P. Shilov. A.B. Yusov, M.N. Sokohva. A.M. Fedoseev, 2008, published in Radiokhimiya, 2008, Vol. 50. No. 3, pp. 203–208.  相似文献   
244.
The formal potential of the couple of nonoxygenated U5+/U4+ ions bound in complexes with unsaturated heteropoly anions (HPAs) P2W17O6110− (I) and SiW11 O398− (II) in 0–1 M NaNO3 and 1 M (NaCl + HCl) in the range of pH 0.7–4.7 was measured. In 1 M NaNO3 solutions at pH 4.7–3.0 for I and 4.3–3.9 for II, the formal potentials are constant: 0.820 and 0.730 V, respectively. They preserve approximately the same value with a decrease in pH to 0.7 in 1 M (NaCl + HCl). The potential noticeably decreases with a decrease in the NaNO3 or NaCl concentration from 1 M to 0 (pH 4.1–4.7): to 0.09 and 0.05–0.06 V for I and II, respectively. Approximate constancy of the potential of the U5+/U4+ couple with a decrease in pH to 1 and lower distinguishes this couple from the M4+/M3+ couples (M = Ce, Am, Bk) whose potential appreciably grows with increasing acidity. This is due to the fact that the U5+ and M4+ ions in acid solutions remain in the form of complexes with the ratio M: HPA = 1: 2, whereas the M3+ ions pass into the form of 1: 1 complexes. Thus, variation of the formal potentials of all the M n + 1/M n+ couples in the presence of H+ and Na+ ions is associated with variation of the stability constants of the complexes M(HPA)2, which, in turn, is caused by interaction of single-charged ions with HPA. However, the H+ and Na+ ions interact with HPA by different mechanisms and therefore affect the potential of the U5+/U4+ couple differently. Original Russian Text ? V.P. Shilov, A.B. Yusov, A.M. Fedoseev, Ph. Moisy, 2008, published in Radiokhimiya, 2008, Vol. 50, No. 5, pp. 393–396.  相似文献   
245.
A procedure was suggested for the synthesis of Np(VII) compounds by electrochemical oxidation in acetate solutions. The conditions for preparing compounds of type MNpO4·nH2O, where M is a single-charged cation of alkali metals, ammonium, silver, guanidinium, or tetraalkylammonium, and of Np(VII) compounds with double-charged cations of alkaline-earth metals, Cu, Cd, and Zn were studied in detail. The compounds were characterized by chemical analysis and by IR and electronic spectroscopy.  相似文献   
246.
The complexes [NpO2(DMSO)5](ClO4)2 (1) and [PuO2(DMSO)5](ClO4)2 (2), isostructural to the known uranyl complex, were synthesized in the form of single crystals. Their crystallographic characteristics were determined by single crystal X-ray diffraction. The IR and electronic absorption spectra of the crystalline U(VI), Np(VI), and Pu(VI) complexes were measured and analyzed.  相似文献   
247.
Published data on the structure of Np ions in acid and alkali solutions, on hydrolysis of Np ions and their complexation with anions and cations, on their redox reactions with water and with each other (disproportionation, reproportionation), and on the effect of anions on this process are analyzed. Possible directions of research in chemistry of Np ions are outlined.  相似文献   
248.
A new method is proposed to determine the content of alcohol in dielectric liquids. The method is based on measuring the attenuation of a wave propagating in a rectangular waveguide with a longitudinal slot in its narrow wall, immersed in a liquid under test. The propagation constant of the H 10 mode in such a waveguide is calculated numerically for various parameters of the medium and the waveguide. It is shown that the attenuation of the wave depends on the parameters of the dielectric medium outside the waveguide. Experiment is carried out on two different types of waveguide at frequencies from 29 to 37 GHz with a solution of ethyl alcohol in water as the external medium. The results of the measurements show that the method can be used for the on-line measurement of alcohol concentration during fermentation.  相似文献   
249.
Various procedures for preparing dopamine labeled with deuterium (2H) and tritium (3H) were considered. The labeled dopamine into which the hydrogen isotopes were introduced by solid-phase halogenation contained, on the average, 2.8 2H (3H) atoms. The labeled dopamine prepared by solid-phase isotope exchange using nanodiamonds as support contained, on the average, 4.8 2H (3H) atoms. The process was accompanied by the substrate deamination; as a result, the yield of the labeled analog was low (7–10%). Mass spectrometric analysis shows that the phenolic fragments formed by the dopamine deamination undergo dimerization.  相似文献   
250.
Published data on the kinetics of Ce(III) oxidation with ozone in HNO3 solutions are analyzed. The formation of peroxynitrite in the course of ozonation of nitric acid solutions, hypothesized previously in the literature, is confirmed. Peroxynitrite is capable to oxidize Ce(III), but with time it decomposes to HNO2 and H2O2, which reduce Ce(IV). Similar phenomenon is observed in ozonation of nitric acid solutions of berkelium.  相似文献   
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