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Neutral hydroxylamine extracts of wheat contained a product that was colourless at pH<5 (λmax 340 nm) and yellow at pH>9 (λmax 400 nm). ESI-MS showed a major ion m/z 184.0 and a possible parent ion m/z 367.2 (MH+) suggesting that the product resulted from the reaction of 2,6-dimethoxy-p-quinone with hydroxylamine. However, mass spectral and other spectroscopic data indicated that the compound was neither of the 2,6-dimethoxy-p-quinone oximes. A product with identical absorbance, mass spectrum, electrophoretic mobility and HPLC retention time as the pigment from hydroxylamine extracts of flour was observed amongst the reaction products of hydroxylamine and 1,4-dihydroxy-2,6-dimethoxybenzene. The structure of this product was identified by NMR, 2D NMR and IR as 4,4′-dihydroxy-3,3′,5,5′-tetramethoxyazodioxybenzene. 相似文献
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At 4.2-350 K, the steady-state and time-resolved emission and excitation spectra and luminescence decay kinetics were studied under excitation in the 2.5-15 eV energy range for the undoped and Ce3+-doped Lu3Al5O12 (LuAG) single-crystalline films grown by liquid phase epitaxy method from the PbO-based flux. The spectral bands arising from the single Pb2+-based centres were identified. The processes of energy transfer from the host lattice to Pb2+ and Ce3+ ions and from Pb2+ to Ce3+ ions were investigated. Competition between Pb2+ and Ce3+ ions in the processes of energy transfer from the LuAG crystal lattice was evidenced especially in the exciton absorption region. Due to overlap of the 3.61 eV emission band of Pb2+ centres with the 3.6 eV absorption band of Ce3+ centres, an effective nonradiative energy transfer from Pb2+ ions to Ce3+ ions takes place, resulting in the appearance of slower component in the luminescence decay kinetics of Ce3+ centres and decrease of the Ce3+-related luminescence intensity. 相似文献
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We study procurement auctions in which, as is common in practice, a group of sellers (incumbents, qualified bidders) is given an advantage, based, for example, on better reliability, quality, or incumbency status. We show conditions under which for any given first price handicap auction, there is a simple second-price design which dominates it. This generalizes a previous result for the case of an auction with one insider and one outsider (Mares and Swinkels in J Econ Theory, 2013) and sharpens our understanding of the classical result by Maskin and Riley (Rev Econ Stud 67:413–438, 2000). 相似文献
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Cr3+ multisites in an yttrium aluminium garnet host have been observed. The absorption, emission and excitation spectra and decay curves have been recorded. With the help of a high-resolution dye laser, the 2E and 4A2 splittings were measured. 相似文献
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A method is proposed for the determination of natural frequencies and mode shapes of a system which is constrained so that unknown stiffnesses are replaced by rigid connections. The constraint is not imposed physically but only in mathematics so that the behaviour of the constrained system is inferred from the unconstrained measurements. Since stiffnesses which are made rigid cannot experience any elastic strain they can have no effect on the inferred measurements. A procedure for comparing the inferred measurements with similarly constrained finite element predictions can be used to determine modelstructure errors. Damage, such as a crack in a beam, can be located by comparing the inferred measurements from the structure in its undamaged and current states. It is demonstrated how unmeasured rotations may be constrained by using rigidbody modes and a reduction/expansion transformation from a finite element model.Sommario. Viene proposto un metodo per la determinazione delle frequenze proprie e dei modi di vibrazione di un sistema vincolato in modo tale che alcuni elementi elastici siano sostituiti da collegamenti rigidi. Il vincolo non viene imposto fisicamente, ma solo matematicamente, e pertanto il comportamento del sistema vincolato viene dedotto dalle misure sul sistema non vincolato. Poiché gli elementi che sono resi rigidi non possono subire alcuna deformazione elastica, essi non hanno certamente alcun effetto sulle misure dedotte per il sistema vincolato. Una procedura che mette a confronto le misure dedotte per il sistema vincolato con le previsioni fornite da un modello ad elementi finiti con analoghi vincoli, può essere utilizzata per determinare errori nella struttura del modello. Danni del tipo di una cricca su una trave possono essere localizzati confrontando le misure dedotte – per sistemi analogamente vincolati – da quelle effettuate sulla struttura non danneggiata e sulla struttura danneggiata. Si dimostra come si possono imporre vincoli sulle rotazioni (non misurate) utilizzando i modi di corpo rigido dell'elemento e una tecnica di riduzione/espansione dei gradi di libertà di un modello ad elementi finiti. 相似文献