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171.
Robert M. Hazen Larry W. Finger Joseph W.E. Mariathasan 《Journal of Physics and Chemistry of Solids》1985,46(2):253-263
Unit-cell parameters and crystal structures of CaWO4(scheelite) and CaMoO4 (powellite) have been determined at several pressures to 5 8 GPa, and unit-cell parameters of PbMoO4 (wulfemte), PbWO4 (stolzite) and CdMoO4 have been measured at pressures to 6 0 GPa All five tetragonal scheelite-type compounds compress anisotropically, with the (itc) axis 1 2 to 1 9 times more compressible than a. In both CaWO4 and CaMoO4 the cation tetrahedra (with W6+ or Mo6+) behave as rigid structural elements with no observed cation-oxygen compression (W-O and Mo-O bond compression < 0001 GPa?1) Compression of the eight-coordinated calcium polyhedron, on the other hand, is comparable to bulk compression of the compounds (Ca-O bond compression = 0005 ± 0 001 GPa?1) Amsotropies in the pressure response of the calcium polyhedron, which is more compressible parallel to c than perpendicular to c, result in the amsotropic unit-cell compression Bulk moduli of the five compounds (with K' assumed to be 4) are CaWO4 (68 ± 9 GPa), CaMoO4 (81 5 ± 0 7 GPa), PbWO4 (64 ± 2 GPa), PbMoO4 (64 ± 2 GPa), and CdMoO4 (104 ± 2 GPa) No reversible transitions to the monoclinic (fergusomte) distortion of scheelite were observed in these compounds Pressure-volume data for PbWO4, however, display strong positive curvature (K'calc) = 23 ± 2) up to about 5 GPa, at which pressure crystals appear to undergo a first-order phase transition The relatively large curvature may be a premonitory effect pnor to a reconstructive transition Structural changes in these compounds with increasing pressure are qualitatively similar to changes that result from isobanc cooling or substitution of a smaller cation in the eight-coordinated site. 相似文献
172.
Peter G. Thompson Larry T. Taylor Bruce E. Richter Neil L. Porter John L. Ezzell 《Journal of separation science》1993,16(12):713-716
A polarity test mix consisting of acetophenone, N, N-dimethylaniline, naphthalene, decanoic acid, 2-naphthol, and n-tetracosane was spiked onto sand, and extracted with supercritical carbon dioxide, to evaluate the collection efficiency of various solvents and solvent mixtures. Nine single collection solvent systems and four mixed collection solvent systems were studied. When one-component collection solvents were employed, quantitative (above 90%) recovery of all analytes was not possible. With mixed collection solvents, recoveries of 90% or better with all analytes studied were possible. 相似文献
173.
Carbon-13 chemical shifts have been obtained in the pulse Fourier transform mode on the following cholinergic neural transmission agents: acetylcholine, β-methyl acetylcholine, carbamoyl choline, choline, tetramethylammonium, scopolamine, atropine, methyl atropine, tropine, tropic acid, nicotine, dimethyl phenylpiperazinium, arecoline, oxotremorine and pilocarpine. The effects of structural variations, asymmetric centers and steric interactions on the 13C shielding are considered. The observed chemical shifts do not appear to correlate simply with potencies in the cholinergic nervous system. 相似文献
174.
Chantal Degrand L. Roullier Larry L. Miller Baruch Zinger 《Journal of Electroanalytical Chemistry》1984,178(1):101-111
Chemically modified carbon electrodes are prepared which hold polymeric layers of anthraquinone or dopamine units on the surface. In each case only those quinonoid units nearest the carbon are electroactive in neutral solution. Other units can be activated by one-electron redox shuttles dissolved in the solution phase which help propagate the redox process through the film. Cobalticinium dicarboxylic acid and methyl viologen are used to catalyze reductive reactions and ferrocene carboxylic acid catalyzes the oxidative propagation. 相似文献
175.
Larry J Gerstein 《Journal of Number Theory》1973,5(5):332-338
Orthogonal splitting for lattices on quadratic spaces over algebraic number fields is studied. It is seen that if the rank of a lattice is sufficiently large, then its spinor genus must contain a decomposable lattice. Also, splitting theory is used to obtain a lower bound for the class number of a lattice (in the definite case) in terms of its rank, via the partition function. 相似文献
176.
Three methods for hromination of pyrimidine were investigated: ( a ) the bromination of pyrimidine hydrochloride in aromatic solvents, ( b ) the vapor phase bromination of pyrimidine, and ( c ) the pyrolysis of pyrimidine hydrochloride perbromide. The addition of bromine to a slurry of pyrimidine hydrochloride in nitrobenzene proved to be superior and afforded excellent yields of 5-bromopyrimidine. 相似文献
177.
178.
Cytotoxicity of organotin compounds is assessed and their effectiveness against leukemia is discussed. The functional groups attached to the tin atom in organotin compounds control the cytotoxicity of the compound towards the thymus gland. The four organotin moieties which have the greatest toxic effect upon the thymus gland are the tri-n-butyltin, di-n-butyltin, tri-n-propyltin and di-n-octyltin groups. Compounds containing these groups also exhibit the poorest test-control ratio (T/C) values when tested as anti-cancer agents against leukemic mice using NCI protocol. 相似文献
179.
180.
A.Larry Wright 《Journal of multivariate analysis》1982,12(2):178-185
Two related almost sure limit theorems are obtained in connection with a stochastic process {ξ(t), ?∞ < t < ∞} with independent increments. The first result deals with the existence of a simultaneous stabilizing function H(t) such that for almost all sample functions of the process. The second result deals with a wide-sense stationary process whose random spectral distributions is ξ. It addresses the question: Under what conditions does converge as T → ∞ for all τ for almost all sample functions? 相似文献