A new salicin derivative from the stem bark of Populus davidiana

Phytochemical study on the BuOH-soluble fraction of the stem bark of Populus davidiana resulted in the isolation of a new salicin derivative(1),named davidianoside.The structure was elucidated on the basis of extensive physicochemical and spectroscopic analyses.     

Correlation between the Cu/Al Value and Activity of Cu-ZSM-5 Catalysts and the Chemical Nature of the Starting Copper Salt

Cu-ZSM-5 catalysts for the selective reduction of NO with propane were obtained by ion exchange between H-ZSM-5 zeolite and an aqueous or aqueous ammonia solution of a copper salt (acetate or nitrate). Their Cu/Al values (%) defined as 2 × 100 (Cu : Al), where Cu : Al is the copper-to-aluminum atomic ratio, were determined as a function of ion exchange pH, which was varied by changing the copper salt and solution concentration. Cu/Al is primarily determined by the chemical nature of the starting copper salt. For a given salt, it is governed by the salt concentration in the solution. At a fixed salt concentration, Cu/Al is always larger for copper acetate than for copper nitrate. It can be raised to ≫100% by using an aqueous ammonia solution of a copper salt. Furthermore, it increases with increasing Si/Al in the starting zeolite if the other ion exchange conditions are equal. Irrespective of preparation conditions, the catalytic activity of Cu-ZSM-5 grows in proportion to Cu/Al. It peaks at Cu/Al ∼ 100% and then remains constant up to Cu/Al ∼ 400%. In order to achieve Cu/Al ∼ 100%, it is most appropriate to use a copper acetate solution.__________Translated from Kinetika i Kataliz, Vol. 46, No. 4, 2005, pp. 652–656.Original Russian Text Copyright © 2005 by Tsikoza, Matus, Ismagilov, Sazonov, Kuznetsov.     

Stability with respect to the initial data and monotonicity of an implicit difference scheme for a homogeneous porous medium equation with a quadratic nonlinearity

We study the stability and monotonicity of a conservative difference scheme approximating an initial-boundary value problem for a porous medium equation with a quadratic nonlinearity under certain conditions imposed only on the input data of the problem. We prove a grid analog of the Bihari lemma, which is used to obtain a priori estimates for higher derivatives; these estimates are needed both in the proof of the continuous dependence of the solution on small perturbations in the input data and for the analysis of monotonicity in the nonlinear case. We show that, regardless of the smoothness of the initial condition, the higher derivatives can become infinite in finite critical time. We give an example in which there arises a runningwave solution, which justifies the theoretical conclusions.     

Structural studies and T c dependence in La2−x Dy x Ca y Ba2Cu4+y O z type mixed oxide superconductors

A new series of mixed oxide superconductors with the stoichiometric composition La_2−x Dy _x Ca _y Ba₂Cu_4+y O _z (x=0.0 − 0.5, y=2x) has been studied for structural and superconductiong properties. Our earlier studies on La_2−x (Y/Er) _x Ca _y Ba₂Cu_4+y O _z series, show a strong dependence of T _c on hole concentration (p _sh). In the present work, the results of the analysis of the neutron diffraction measurements at room temprerature on x=0.3 and 0.5 samples are reported. It is interesting to know that Ca substitutes for both La and Ba site with concomitant displacement of La onto Ba site. Superconductivity studies show that maximum T _c is obtained for x=0.5, y=1.0 sample (T _c ∼ 75 K), for La_1.5Dy_0.5Ca₁Ba₂Cu₅O _z (La-2125).     

On the role of conservation laws in the problem on the occurrence of unstable solutions for quasilinear parabolic equations and their approximations

For a broad class of initial-boundary value problems for quasilinear parabolic equations with nonlinear source and their approximations, we show that if the initial energy is negative, then the solution always blows up in finite time. This is especially important for finding sufficiently simple and easy-to-verify conditions guaranteeing the presence of physical effects such as heat localization in peaking modes or thermal explosions and for deriving two-sided estimates of the solution lifespan. We construct the corresponding new classes of difference schemes for which grid analogs of integral conservation laws hold. We show that, to obtain efficient two-sided estimates for the blow-up time of the solution of the differential problem, in practice, one should use difference schemes with explicit as well as implicit approximation to the source.     

Untersuchungen zur Bildung von Molekülionen in Funken- und Laserplasmen

Zusammenfassung Mit Hilfe eines massenspektrographischen Systems, bestehend aus einer Nd: YAG-Laser- oder einer Funken-Ionenquelle und einem doppeltfokussierenden Massenspektrographen vom Mattauch-Her-zog-Typ, wurde die Bildung von Molekülionen in Laser- und Funkenplasmen untersucht. Die Häufigkeitsverteilung der nachgewiesenen Cluster- und Molekülionen im untersuchten Graphit und Uranylnitrat wurde in Laser- und Funken-Massenspektren verglichen.

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Investigation of the formation of molecular ions in spark and laser plasmas

Summary A mass spectrometer system consisting of a Nd: YAG laser or a spark ion source and a double focusing mass spectrograph of the Mattauch-Herzog type was used to investigate the formation of molecular ions in laser and spark plasmas. The abundance of the cluster and molecular ions in the investigated graphit and uranylnitrate detected was compared in laser and spark mass spectrum.

     

Hydrothermal treatment of silica gel

Summary A simple procedure was developed for preparing wide pore (≦ 40nm) silicas from a common chromatographic silica gel. The effects of various experimental conditions on pore size, pore volume, and surface area are discussed. The results show that under controlled conditions a wide variety of wide pore silica packing materials can be prepared. Presented at the 15th International Symposium on Chromatography, Nürnberg, October 1984     

Reisolation of Carotenoid 3,6-Epoxides from Red Paprika (Capsicum annuum)

Cucurbitaxanthin A (= (3S,5R,6R,3′R)-3,6-epoxy-5,6-dihydro-β,β- carotene-5,3′-diol; 5 ), cucurbitaxanthin B (= (3S,5R,6R,3′S,5′R,6′S)-3,6,5′, 6′-diepoxy-5,6,5′,6′-tetrahydro-β,β-carotene-5,3′-diol; 6 ), the epimeric cucurbitachromes 1 and 2 (= (3S,5R,6R,3′S,5′R,8′S)- and (3S,5R,6R,3′S,5′R,8′R)-3,6,5′, 8′-diepoxy-5,6,5′,6′-tetrahydro-β,β-carotene-5,3′-diol, resp.; 9/10 ), cycloviolaxanthin (= (3S,5R,6R,3′S,5′R,6′R)-3,6,3′, 6′-diepoxy-5,6,5′,6′-tetrahydro-β,κs-carotene-5,5′-diol; 8 ), and capsanthin 3,6-epoxide (= (3S,5R,6R,3′S,5′R)-3,6-epoxy-5,6-dihydro ?5,3′-dihydroxy-β,κ-caroten-6′-one; 7 ) were isolated from red spice paprika (Capsicum annuum var. longum) and characterized by their ¹H- and ¹³C-NMR, mass, and CD spectra.