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1.
In this note we consider asymptotic results for self-intersections of closed geodesics on surfaces for which the angle of the intersection occurs in a given arc. We do this by extending Bonahon's definition of intersection forms for surfaces.
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Michael Sharp 《Analytica chimica acta》1976,85(1):17-30
The primary redox reactions for solid-state ion-selective electrodes prepared from electronically semiconducting salts of 7,7,8,8-tetracyanoquinodimethane (tcnq) can be identified by considering the redox properties of their constituent ions or molecules. Three different processes involving the couples, Mn+/M0, 2tcnqo/(tcnq-)2 and (tcnq-)2/2tcnq2- are possible depending on salt composition. Ionic product values determined by potentiometric and atomic absorption methods are in excellent agreement for several such salts; Ks(K2tcnq2)=5.8±1.2·10-11(pot.), 1.7±1·10-11 (a.a.s.); Ks(Cdtcnq2) = 3.0±0.5·10-9 (pot.), 2.9±0.3·10-9(a.a.s.); Ks(Pbtcnq2) = 1.3±0.3·10-10 (pot.), 0.96±0.2·10-10(a.a.s.); and indicate that the lower activity limit for electrode response is controlled by the solubility of the sensor material itself. Comparisons of predicted and observed standard electrode potentials provide quantitative support for an ion-exchange mechanism of interference. The behaviour of electrodes prepared from Cu2tcnq2 (copper(I)) and Cutcnq2 (copper(II)) is explained on the basis of an interference mechanism and considerations of solid-state equilibria. 相似文献
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Derivatization of a variety of peptides by a method known to enhance anhydride formation is demonstrated by mass spectrometry to yield ions that have elemental composition and fragmentation properties identical to [b(n-1) + OH + H]+ ions formed by gas-phase rearrangement and fragmentation. The [b(n-1) + OH + H]+ ions formed by gas-phase rearrangement and fragmentation and the solution-phase [b(n-1) + OH + H]+ ion structural analogs formed by derivatization chemistry show two different forms of dissociation using multiple-collision CAD in a quadrupole ion trap and unimolecular decomposition in a TOF-TOF; one group yields identical product ions as a truncated form of the peptide with a free C-terminal carboxylic acid and fragments at the same activation energy; the other group fragments differently from the truncated peptide, being more resistant to fragmentation than the truncated peptide and yielding primarily the [b(n-2) + OH + H]+ product ion. Nonergodic electron capture dissociation MS/MS suggests that any structural differences between the specific-fragmenting [b(n-1) + OH + H]+ ions and the truncated peptide is at the C-terminus of the peptide. The specific-fragmentation can be readily observed by MS(n) experiments to occur in an iterative fashion, suggesting that the C-terminal structure of the original [b(n-1) + OH + H]+ ion is maintained after subsequent rearrangement and fragmentation events in peptides which fragment specifically. A mechanism for the formation of specific-fragmenting and nonspecific-fragmenting [b(n-1) + OH + H]+ ions is proposed. 相似文献
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An improved experimental arrangement for the determination of kinetic data relating to polarographic reductions is described. The significant feature is the constant-temperature reference electrode; its construction and use in this context are described. A comparison is made of the more realistic results obtained by these means, with those obtained with a more conventional cell where the temperature of the reference electrode is varied with that of the working solution. 相似文献
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The SHS route is based on the well-known thermite reaction, in which a strongly exothermic reaction can sustain itself and propagate in the form of a combustion wave until the reactants have been completely consumed. The successful application of the method to the synthesis of superconducting ceramics of stoichiometry RBa2Cu3Oy (R=Y, Er, Yb) is reported. The 123 phase was obtained when pellets of R2O3, BaO2 and Cu metal in the correct proportions were dropped into a heater held at 800°C in an oxygen atmosphere and left there for only 10 minutes. Thermal methods (DSC and DTA) are excellent techniques with which to investigate the dependence of the reaction on heating rate, atmosphere and starting composition. 相似文献