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Hella Folkerts Kurt Dehnicke Jrg Magull Helmut Goesmann Dieter Fenske 《无机化学与普通化学杂志》1994,620(7):1301-1306
Phosphorane Iminato-Trichloroselenates(II): Syntheses and Crystal Structures of [SeCl(NPPh3)2]+SeCl3? and [Me3SiN(H)PMe3]2+[Se2Cl6]2? [SeCl(NPPh3)2]+SeCl3? has been synthesized by the reaction of Se2Cl2 with Me3SiNPPh3 in acetonitrile solution, forming orangered crystals, whereas red crystals of [Me3SiN(H)PMe3]2+[Se2Cl6]2? were obtained by the reaction of Me3SiNPMe3 with SeOCl2 in acetonitrile solution. Both complexes were characterized by X-ray structure determinations. [SeCl(NPPh3)2]+SeCl3?: Space group P21/n, Z = 4, structure solution with 7 489 observed unique reflections, R = 0.057. Lattice dimensions at ?60°C: a = 1 117.0; b = 2 241, c = 1 407.5 pm, β = 95.61°. In the cation [SeCl(NPPh3)2]+ the selenium atom is φ-tetrahedrally coordinated by the chlorine atom and by the nitrogen atoms of the phosphorane iminato ligands, whereas the anion SeCl3? has a T-shaped structure with φ-trigonal-bipyramidale surrounding of the selenium atom. [Me3SiN(H)PMe3]2+[Se2Cl6]2?: Space group P21/c, Z = 4, structure solution with 2 093 observed unique reflections, R = 0.080. Lattice dimensions at ?70°C: a = 956, b = 828, c = 1 973 pm, β = 93.80°. The structure consists of [Me3SiN(H)PMe3]+ ions and planar [Se2Cl6]2? anions, in which the selenium atoms are bridged nearly symmetrically by two chlorine atoms. 相似文献
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The need to develop reliable and efficient adaptive algorithms using mixed finite element methods arises from various applications in fluid dynamics and computational continuum mechanics. In order to save degrees of freedom, not all but just some selected set of finite element domains are refined and hence the fundamental question of convergence requires a new mathematical argument as well as the question of optimality. We will present a new adaptive algorithm for mixed finite element methods to solve the model Poisson problem, for which optimal convergence can be proved. The a posteriori error control of mixed finite element methods dates back to Alonso (1996) Error estimators for a mixed method. and Carstensen (1997) A posteriori error estimate for the mixed finite element method. The error reduction and convergence for adaptive mixed finite element methods has already been proven by Carstensen and Hoppe (2006) Error Reduction and Convergence for an Adaptive Mixed Finite Element Method, Convergence analysis of an adaptive nonconforming finite element methods. Recently, Chen, Holst and Xu (2008) Convergence and Optimality of Adaptive Mixed Finite Element Methods. presented convergence and optimality for adaptive mixed finite element methods following arguments of Rob Stevenson for the conforming finite element method. Their algorithm reduces oscillations, before applying and a standard adaptive algorithm based on usual error estimation. The proposed algorithm does this in a natural way, by switching between the reduction of either the estimated error or oscillations. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
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In this paper we prove that thek-ary fragment of transitive closure logic is not contained in the extension of the (k–1)-ary fragment of partial fixed point logic by all (2k–1)-ary generalized quantifiers. As a consequence, the arity hierarchies of all the familiar forms of fixed point logic are strict simultaneously with respect to the arity of the induction predicates and the arity of generalized quantifiers.Although it is known that our theorem cannot be extended to the sublogic deterministic transitive closure logic, we show that an extension is possible when we close this logic under congruence.Supported by a grant from the University of Helsinki. This research was initiated while he was a Junior Researcher at the Academy of FinlandThis article was processed by the author using the LATEX style filepljourlm from Springer-Verlag. 相似文献
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Hella Folkerts Kurt Dehnicke Ccilia Maichle-Mssmer Joachim Strhle 《无机化学与普通化学杂志》1995,621(7):1171-1174
Synthesis and Crystal Structure of the Selenyl-Phosphoraneiminato Complex SeO(NPPh3)2 SeO(NPPh3)2 has been prepared from SeO2 and Me3SiNPPh3 in a SeO2 suspension in acetonitrile, forming colourless crystals. The compound is characterized by IR spectroscopy and by a crystal structure determination. Space group P1 , Z = 2, structure solution with 5 344 observed unique reflections, R = 0.064. Lattice dimensions at ?40°C: a = 931.6, b = 947.6, c = 1 762 pm, α = 77.50°, β = 81.78°, γ = 79.23°. The compound forms monomeric molecules in which the selenium atom is φ-tetrahedrally surrounded with bond lengths SeO = 161.7 pm and SeN = 179.9 and 181.6 pm. 相似文献