Kinetics of the formation of precipitates and the physicochemical properties of technetium-99 and rhenium sulfides according to small-angle X-ray scattering and ultramicrocentrifugation data

International audienceThe interaction of technetium and rhenium with sulfides in aqueous solutions was studied by small-angle X-ray scattering and ultramicrocentrifugation. It was shown that, although the stoichiometry of technetium sulfide corresponds to the formula Tc2S7–x , the oxidation state of technetium in it is +4 and the excess sulfur is bound into a disulfide group so that its formula can correctly be written as [Tc3(µ3-S)(µ2-S2)3(S2)(3n–n)/n)] n . The determination of the solubility of technetium sulfide is complicated by its tendency to form colloids, which was the reason why the above methods were chosen to find features of its formation and describe its solubility in solutions

Combined method for identifying the parameters of a distributed dynamic model

Предложен комбинированный метод идентификации уравнений математической физики, описывающих динамику пространственно-распределенных процессов, на основе экспериментальных многомерных временных рядов. Первым этапом метода является получение МНК-оценок параметров многомерной авторегрессии. Однако, эти оценки оказываются смещенными в силу наличия ошибок в регрессорах. С целью уменьшения указанного смещения в качестве второй составляющей метода применяется расширенный фильтр Калмана. Приводится вычислительный эксперимент, подтверждающий эффективность предложенной методики.//A combined method for identifying the equations of mathematical physics describing the dynamics of spatially-distributed processes on the basis of experimental multidimensional time series is proposed. The first stage of the method is the derivation of OLS estimators of multidimensional autoregression parameters. However, these estimates are biased due to the presence of errors in the regressors. To reduce this bias, the extended Kalman filter as the second component of the method is used. A computational experiment confirming the effectiveness of the proposed technique is presented

Spin density matrix elements in exclusive ρ0\mathrm{\rho^0} electroproduction on 1H\mathrm{^1H} and 2H\mathrm{^2H} targets at 27.5 GeV beam energy

Spin Density Matrix Elements (SDMEs) describing the angular distribution of exclusive rho^0 electroproduction and decay are determined in the HERMES experiment with 27.6 GeV beam energy and unpolarized hydrogen and deuterium targets. Eight (fifteen) SDMEs that are related (unrelated) to the longitudinal polarization of the beam are extracted in the kinematic region 1 GeV^2 < Q^2 < 7 GeV^2, 3.0 GeV < W < 6.3 GeV, and -t < 0.4 GeV^2. Within the given experimental uncertainties, a hierarchy of relative sizes of helicity amplitudes is observed. Kinematic dependences of all SDMEs on Q^2 and t are presented, as well as the longitudinal-to-transverse rho^0 electroproduction cross section ratio as a function of Q^2. A small but statistically significant deviation from the hypothesis of s-channel helicity conservation is observed. An indication is seen of a contribution of unnatural-parity-exchange amplitudes; these amplitudes are naturally generated with a quark-exchange mechanism.Comment: 41 pages, 20 figures, 16 table; revised version corrects small typos, text clarified on 6 pages, two references added and new data added to figure 2