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排序方式: 共有216条查询结果,搜索用时 31 毫秒
31.
Flix Zamora Pilar Amo-Ochoa Birgit Fischer Arnd Schimanski Bernhard Lippert 《Angewandte Chemie (International ed. in English)》1999,38(15):2274-2275
Not only UV radiation can bring about the dimerization of the pyrimidine nucleobase uracil, a metal ion can as well! The reaction proceeds by a reductive elimination process of two cis-oriented uracil entities, each bonded to AuIII through C5 [Eq. (a)]. R/R′=H/CH3, CH3/CH3, H,C5H9O4 相似文献
32.
Horst Kunkely Dr. Arnd Vogler Prof. Dr. 《Angewandte Chemie (International ed. in English)》2009,48(9):1685-1687
Last but not least : A simple molecular redox system is used to split water into hydrogen and oxygen photochemically. Two separate photolyses are combined to a cyclic process (see scheme). Osmocene ([Cp2OsII] with Cp?=C5H5?) serves as photocatalyst.
33.
Lightweight construction plays an important role in the global task to save energy. A common approach to reduce the weight of structures is the use of composite materials like fibre reinforced polymers (FRP). FRP can be characterised by transversely isotropic material behaviour, a special case of anisotropy. In our arcticle we present the necessary efforts to include such material behaviour into an existing adaptive FEM code. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
34.
Thomas Apel Johannes Pfefferer Arnd R?sch 《Computational Optimization and Applications》2012,52(1):3-28
A specific elliptic linear-quadratic optimal control problem with Neumann boundary control is investigated. The control has to fulfil inequality constraints. The domain is assumed to be polygonal with reentrant corners. The asymptotic behaviour of two approaches to compute the optimal control is discussed. In the first the piecewise constant approximations of the optimal control are improved by a postprocessing step. In the second the control is not discretized; instead the first order optimality condition is used to determine an approximation of the optimal control. Although the quality of both approximations is in general affected by corner singularities a convergence order of 3/2 can be proven provided that the mesh is sufficiently graded. 相似文献
35.
We discuss the full discretization of an elliptic optimal control problem with pointwise control and state constraints. We
provide the first reliable a-posteriori error estimator that contains only computable quantities for this class of problems.
Moreover, we show, that the error estimator converges to zero if one has convergence of the discrete solutions to the solution
of the original problem. The theory is illustrated by numerical tests. 相似文献
36.
We study the existence of dislocations in an anisotropic Swift-Hohenberg equation. We find dislocations as traveling or standing waves connecting roll patterns with different wavenumbers in an infinite strip. The proof is based on a bifurcation analysis. Spatial dynamics and center-manifold reduction yield a reduced, coupled-mode system of differential equations. Existence of traveling dislocations is then established by showing that this reduced system possesses robust heteroclinic orbits. 相似文献
37.
Johannes Reisch Arnd A. W. Voerste Michael Top Peter Dziemba 《Monatshefte für Chemie / Chemical Monthly》1992,123(5):473-475
Summary The natural product noracronycine as well as some of its analogs were synthesized by Mitsunobu-etherisation, using propinol derivatives.
Acetylenchemie, 22. Mitt.: Synthese von Noracronycin und einiger Analoga mittels Mitsunobu-Reaktion (Kurze Mitt.)
Zusammenfassung Der Naturstoff Noracronycin sowie einige seiner Analoga konnten durch Mitsunobu-Veretherung unter Verwendung von Propinol-Derivaten synthetisiert werden.相似文献
38.
Complexes of Rhenium with Planar ReN2S2 Rings. Syntheses and Crystal Structures of AsPh4[ReCl4(N2S2)] and PPh4[ReBr4(N2S2)] The complex [ReCl4(N2S2)]? can be obtained as PPh4⊕ or AsPh4⊕ salt by the action of S(NSiMe3)2 and of diphenylacetylene, respectively, on the chlorothionitrene complex [ReCl4(NSCl)2]?. Another method of synthesis is the reaction of [ReCl3(NSCl)2(POCl3)] with SbPh3. [ReBr3(N2S2)]2 is obtained from excess Me3SiBr and [ReCl3(NSCl)2(POCl3)]. The anionic complex [ReBr4(N2S2)]? forms from either [ReCl4(NSCl)2]? or [ReCl4(N2S2)]? with Me3SiBr. All compounds are black, diamagnetic, and sensitive to moisture; the PPh4⊕ and AsPh4⊕ salts are soluble in CH2Cl2 and CH2Br2. The IR spectra are reported. The crystal structures of AsPh,4[ReCl4(N2S2)] and PPh4[ReBr4(N2S2)] were determined by X-ray diffraction. AsPh4[ReCl4(N2S2)]: space group P2/n, Z = 2, a = 1244.5, b = 1429.3, c = 791.1 pm, γ = 96.89° (1715 observed reflexions, R = 0.082). PPh4[ReBr4[ReBr4(N2S2)]: space group P21/n, Z = 4, a = 961.7, b = 1397.4, c = 2205.7 pm, β = 102.10° (1787 observed reflexions, R = 0.073). In both compounds the [ReX4(N2S2)]? anions have the same type of structure, the Re atoms forming part of planar ReN2S2 rings; the bond lengths are ReN 177 pm, NS 152 pm, and SS 259 for the chloro compound and ReN 184 pm, NS 153 pm, and SS 264 pm for the bromo compound. In AsPh4[ReCl4(N2S2)] the cations are stacked to form columns in the c-direction; in PPh4[ReBr4(N2S2)], there is considerable distortion form this packing principle. 相似文献
39.
Ochiai N Sasamoto K Takino M Yamashita S Daishima S Heiden AC Hoffmann A 《Analytical and bioanalytical chemistry》2002,373(1-2):56-63
A method for the simultaneous determination of seven preservatives - sorbic acid, benzoic acid, and p-hydroxybenzoic acid ethyl, isopropyl, propyl, isobutyl, and butyl esters - in beverages, vinegar, aqueous sauces, and quasi-drug drinks has been developed using the stir-bar sorptive extraction technique then thermal desorption GC-MS analysis. The extraction conditions - pH, sample volume, extraction temperature, salt addition, and extraction time - were examined. d5-Benzoic acid and p-hydroxybenzoic acid sec-butyl ester were added as surrogate internal standards to compensate for the effect of sample matrix and coexisting analytes on the sorptive extraction. The linearity of the method was good over the concentration range from 1 to 1000 microg mL(-1) for sorbic acid, 10-1000 microg mL(-1) for benzoic acid, and 0.1-100 microg mL(-1) for p-hydroxybenzoic acid ethyl, isopropyl, propyl, isobutyl, and butyl esters, and the correlation coefficients were higher than 0.9984. The limit of detection ranged from 0.015 to 3.3 microg mL(-1). The recoveries (95-105%) and precision (RSD: 0.86-6.0%) of the method were examined by analyzing a sparkling soft drink, white wine, red wine, balsamic vinegar, soy sauce, and quasi-drug drink samples fortified at the 5 to 50 microg mL(-1) level. 相似文献
40.