How synthesis parameters influence the quality of lead magnesioniobate PbMg1/3Nb2/3O3

Lead magnesioniobate PbMg_1/3Nb_2/3O₃ (PMN) has been prepared using lead oxide and magnesium niobate. Factors that influence the perovskite/pyrochlore ratio in the PMN structure have been studied. In order for the maximal amount of the perovskite phase to be obtained, synthesis should be carried out at 850?C900°C; an excess of MgO (1?C5 wt %) does not exert a positive effect. An excess of PbO (5?C7 wt %) allows one to obtain a phase that contains 85% PMN, with the perovskite structure. The perovskite lattice is found to be stabilized as a result of cationic substitutions (Yb, Lu) in the Mg-Nb sublattice due to the formation of solid solution Pb(Mg_1/3Nb_2/3)_{1 ? x} Yb(Lu) _x O₃, where 0 ?? x ?? 0.9.     

Kinetics of reduction of palladium(II) complexes with ethylamine on a dropping-mercury electrode

The reduction kinetics of palladium(II) complexes containing ethylamine is studied on a dropping-mercury electrode in solutions of pH 8–13.5 with different ethylamine concentrations in the presence of sodium perchlorate. An irreversible character of the reduction and a diffusion nature of limiting currents are established. Parameters of electrochemical kinetics and diffusion coefficient for the complexes are determined. At pH 11 and 12, the half-wave potential is independent of the ethylamine concentration in the concentration range 0.01 to 0.1 M. Tetraethylamine complexes of palladium(II) predominate in solution and presumably take part in the slow electrochemical step. Raising ethylamine concentration to 2 M makes E _1/2 more negative, due to specific ethylamine adsorption. Limiting currents of two waves, which occur at pH 8 and overall ethylamine concentration 0.01–0.02 M, are used to calculate two constants. One is the step stability constant for complex Pd(eta) ₄ ²⁺ . The other is the equilibrium constant for deprotonation of a ligand in Pd(eta) ₄ ²⁺ , which occurs at pH 13.1–13.5 and ethylamine concentrations 1 and 2 M.     

Short proofs of the elliptic beta integrals

We give elementary proofs of the univariate elliptic beta integral with bases |q|,|p| < 1 and its multiparameter generalizations to integrals on the A _n and C _n root systems. We prove also some new unit circle multiple elliptic beta integrals, which are well defined for |q| = 1, and their p → 0 degenerations. Dedicated to Richard Askey on the occasion of his seventieth birthday. 2000 Mathematics Subject Classification Primary—33D99, 33E05 This work is supported in part by the Russian Foundation for Basic Research (RFBR) grant no. 03-01-00781.     

Inversions of integral operators and elliptic beta integrals on root systems

We prove a novel type of inversion formula for elliptic hypergeometric integrals associated to a pair of root systems. Using the (A,C) inversion formula to invert one of the known C-type elliptic beta integrals, we obtain a new elliptic beta integral for the root system of type A. Validity of this integral is established by a different method as well.     

Elliptic grids, rational functions, and the Padé interpolation

We consider rational functions with n prescribed poles for which there exists a divided difference operator transforming them to rational functions with n−1 poles. The poles of such functions are shown to lie on the elliptic grids. There is a one-to-one correspondence between this problem of admissible grids and the Poncelet problem on two quadrics. Additionally, we outline an explicit scheme of the Padé interpolation with prescribed poles and zeros on the elliptic grids. Dedicated to Richard Askey on the occasion of his seventieth birthday. 2000 Mathematics Subject Classification Primary—42C05; Secondary—39A13, 41A05, 41A21.     

Electrodeposition of Nickel-Chromium Coatings from Chromium(III) Sulfate Electrolytes

The kinetics of electrodeposition of nickel-chromium alloys from chromium(III) sulfate electrolytes containing succinic and malonic acids was studied. The effect exerted by the electrolysis mode and the pH of the electrolyte on the composition and quality of the obtained coatings was investigated. The possibility of obtaining protective and decorative nickel-chromium coatings containing 20-55% chromium is established.     

Determination of electron affinity of carbonyl radicals by means of negative ion mass spectrometry

Appearance energies of [M-H](-) ions from carbonyl compounds R-CO-R' (R,R' = H, CH(3), NH(2), OH) have been measured by means of negative ion mass spectrometry in resonant electron capture mode. Values of electron affinity of the corresponding radicals, CH(2)&dbond;C(X)O, NH&dbond;C(X)O and O&dbond;C(X)O, have been determined. Copyright 1999 John Wiley & Sons, Ltd.     

Oxidation of CO in microchannels of ceramic membranes modified with oxide catalytic coatings

Ceramic and cermet membranes containing catalytic coatings in the internal volume of their channels were obtained. A relationship between the permeability and kinetic regularities of CO oxidation describing the transmembrane flow of gases was studied. The pre-exponential factor and apparent activation energy change as the loading of the membrane channels by the catalyst proceeds. The study of gas permeability through the membranes showed that the catalyst with a loose branched surface is distributed in the membrane microchannels. The reaction rate constant increases in parallel with an increase in the relative fraction of the catalyst surface. The CO oxidation rate is assumed to depend statistically on the number of active sites, which increases with filling of the membrane channels by the catalytic material.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2613–2619, December, 2004.     

Vacuum condensates in supersymmetric gluodynamics

We analyse the restrictions imposed by supersymmetric Ward identities on the dimension-six condensates in supersymmetric gluodynamics. It is shown that the system of the Ward identities admits a nonzero value for the four-fermion condensate \(\left\langle {\left( {\lambda \sigma _\mu T^a \bar \lambda } \right)^2 } \right\rangle _0 \) while 〈f ^abc F _μν ^a F _νρ ^b F _ρμ ^c 〉₀ must vanish.