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991.
Systems with a gauge degeneracy are characterized either by supplementary conditions, or by a set of generators of gauge transformations, or by a set of constraints deriving from Dirac's canonical constraint method. These constraints can be expressed either as conditions on the field algebra , or on the states on . In aC*-algebra framework, we show that the state conditions give rise to a factor algebra of a subalgebra of the field algebra . This factor algebra, , is free of state conditions. In this formulation we show also that the algebraic conditions can be treated in the same way as the state conditions. The connection between states on and states on is investigated further within this framework, as is also the set of transformations which are compatible with the set of constraints. It is also shown that not every set of constraints can give rise to a nontrivial system. Finally as an example, the abstract theory is applied to the electromagnetic field, and this treatment can be generalized to all systems of bosons with linear constraints. The question of dynamics is not discussed. 相似文献
992.
Nataliya V. Kirij Valeria N. Movchun Wieland Tyrra Hendrik T.M. Fischer 《Journal of fluorine chemistry》2008,129(1):14-21
The reactions of non-activated aldimines with trimethyl(trifluoromethyl)silane and 1 equiv. of tetramethylammonium fluoride proceed via the formation of tetramethylammonium amides which were identified by low-temperature 19F NMR experiments. Consecutive reactions of the salts formed in situ with electrophiles yielded trifluoromethylated amines. Fluoride elimination is observed in the absence of electrophilic substrates leading to the formation of difluoromethylated ketimines. 相似文献
993.
We study one-dimensional Schrödinger operators with complex measures as potentials and present an improved criterion for absence of eigenvalues which involves a weak local periodicity condition. As an application we consider quasiperiodic measures as potentials. (© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
994.
This article studies the robustness of confidence interval construction for the intraclass kappa statistic based on a dichotomous response when the assumption of marginal homogeneity across two raters is violated. Two methods of construction are considered: the goodness-of-fit approach and the modified Wald method. Evaluation was done by exact calculation of the confidence interval coverage produced by these approaches. It was found that under mild departures from marginal homogeneity (differences in rater success rates of $<$ 10 %), the goodness- of-fit approach can be recommended. Moreover, under these same conditions, Cohen’s kappa tends to be less biased as a point estimator than the intraclass kappa statistic. 相似文献
995.
We study to which extent all pairs of opposite vertices of self-opposite type determine a given building. We provide complete answers in the case of buildings related to projective spaces, to polar spaces and the exceptional buildings, but for the latter we restrict to the vertices whose Grassmannian defines a parapolar space of point diameter 3. Some results about non-self opposite types for buildings of types ${\mathsf{A}_n}$ , ${\mathsf{D}_m}$ (m odd), and ${\mathsf{E}_6}$ are also provided. 相似文献
996.
997.
Berthold Hoge Dr. Boris Kurscheid Sebastian Peuker Wieland Tyrra Hendrik T. M. Fischer 《无机化学与普通化学杂志》2007,633(10):1679-1685
The reaction of the sterically shielded phosphane derivative, dichlorodiethylaminophosphane, Cl2PNEt2, with an excess of a mixture of 2,6‐bis(trifluoromethyl) and 2,4‐bis(trifluoromethyl)phenyl lithium gives bis[2,4‐bis(trifluoromethyl)phenyl]diethylaminophosphane, [2,4‐(CF3)2C6H3]2PNEt2, in 72 % yield as a colourless solid, while 2,6‐bis(trifluoromethyl)phenyl lithium remains unchanged in solution. The amino derivative crystallizes in the monoclinic space group P21/c (a 869.2(1), b 1857.4(1), c 1357.6(1) pm, β 100.57(4)°, Z = 4). Treatment of [2,4‐(CF3)2C6H3]2PNEt2 in CHCl3 solution with conc. HCl allows the synthesis of [2,4‐(CF3)2C6H3)]2PCl. [2,4‐(CF3)2C6H3]2PCl reacts with H2O in THF solution with quantitative formation of the corresponding secondary phosphane oxide. To obtain bis[2,4‐bis(trifluoromethyl)phenyl]phosphinic acid, [2,4‐(CF3)2C6H3]2P(O)OH, quantitatively, a CHCl3 solution of [2,4‐(CF3)2C6H3]2P(O)H, has to be stirred in an NO2 atmosphere. The phosphinic acid crystallizes is the triclinic space group (a 754.2(1), b 927.6(2), c 1305.5(2) pm, α 85.11(2)°, β 75.45(1)°, γ 79.99(2)°, Z = 2). From the reaction of the phosphinic acid with either elemental sodium or with cyanide salts, the corresponding phosphinate salts are obtained in an almost quantitatively yield. 相似文献
998.
999.
Coq N van Bommel T Hikmet RA Stapert HR Dittmer WU 《Langmuir : the ACS journal of surfaces and colloids》2007,23(9):5154-5160
In this work we explore a new hydrogel stamp material obtained from polymerizing 2-hydroxyethyl acrylate and poly(ethylene glycol) diacrylate in the presence of water for the microcontact printing of proteins directly on gold substrates and by covalent coupling to self-assembled monolayers of alkanethiols. At high cross-link density, the hydrogel is rigid, hydrophilic, and with a high buffer holding capacity to enable the unsupported printing of protein patterns homogeneously and reproducibly, with micrometer-range precision. The stamps were used to print antibodies to human parathyroid hormone, which were shown using immunoassay tests to retain their biological function with binding capacities comparable to those of solution-adsorbed antibodies. 相似文献
1000.
Blank JH Beckers J Collignon PF Clerc F Rothenberg G 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(18):5121-5128
The pros and cons of oxidative dehydrogenation of propane are outlined and a new catalytic system based on metal-doped cerianite catalysts is introduced. These novel materials catalyze the selective combustion of hydrogen from a mixture of hydrogen, propane, and propene at 550 degrees C. This gives three key advantages: energy is supplied directly where needed, product separation is made easier, and the dehydrogenation equilibrium is shifted to the desired products. A set of eighteen doped cerianites was synthesized in parallel, characterized, and screened for activity, selectivity, and stability in a cyclic redox system. The best results were obtained with Ce(0.89)Cr(0.02)Fe(0.09)O(2), Ce(0.98)Sn(0.02)O(2), and Ce(0.96)Cu(0.02)Zn(0.02)O(2), which gave 98 %, 91 %, and 98 % selectivity, respectively. Ce(0.89)Cr(0.02)Fe(0.09)O(2) also shows excellent stability in over 120 cycles (66 h on stream at 550 degrees C). Importantly, these doped cerias are monophasic crystalline materials. The dopants are incorporated as solid solutions throughout the fluorite lattice. This means that these catalysts are very stable (they do not sinter during reduction) as opposed to traditional supported metal oxides. The results show that both activity and selectivity towards hydrogen combustion can be tuned (increased or decreased) by selecting the appropriate dopant. Furthermore, the trends in selectivity differ from those measured on supported oxides of the same elements, which indicates that these novel materials indeed contain unique active sites. The factors governing selectivity towards hydrogen oxidation and the nature of the active site are discussed. 相似文献