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991.
992.
Nishiwaki N Rahbek Knudsen K Gothelf KV Jørgensen KA 《Angewandte Chemie (International ed. in English)》2001,40(16):2992-2995
No AbstractSupporting information for this article is available on the WWW under http://www.angewandte.com or from the author. 相似文献
993.
Kurt Johansson Johansson 《Communications in Mathematical Physics》2001,215(3):683-705
Consider an N×N hermitian random matrix with independent entries, not necessarily Gaussian, a so-called Wigner matrix. It has been conjectured
that the local spacing distribution, i.e. the distribution of the distance between nearest neighbour eigenvalues in some part
of the spectrum is, in the limit as N→∞, the same as that of hermitian random matrices from GUE. We prove this conjecture for a certain subclass of hermitian Wigner
matrices.
Received: 21 June 2000 / Accepted: 26 July 2000 相似文献
994.
Electrical instability in a SI GaAs plates of the semiconductor gas discharge gap system (SGDGS) is studied experimentally in a wide range of the gas pressures, interelectrode distances and different diameters of the cathode areas. While being driven with a stationary voltage, it generates current and discharge light emission (DLE) instabilities with different amplitudes of the oscillation. It is shown that under the experimental conditions the interelectrode distance played only a passive role and was not responsible for the appearance of the DLE instability. At the same time for different diameters D of the GaAs plate areas the expanded range of current and DLE oscillations are observed. SGDGS with an N‐shaped CVC was analyzed using both the current and DLE data showing the electrical instability in the GaAs cathode. It was found that application of high feeding voltage to this cathode give rise to non‐uniform spatial distribution of the DLE, which disturbed the operation of the system. The experiment presents also a new metod to study and visualization of the electrical instabilities in high‐resistivity GaAs plates of large diameter. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
995.
996.
Hermann Poschenrieder Eduard Eckl Hans‐Dietrich Stachel Andreas Windt Kurt Polborn 《Journal of heterocyclic chemistry》2000,37(4):839-846
The 4‐hydroxypyridones 7 and 3‐hydroxypyridones 8/9 (azagrevellins) were prepared by reaction of the pyrrolidinetrione 4 and diazoalkanes. The ring enlargement proceeded by anionotropic [1,2]‐rearrangement introducing carbon between C‐3 and C‐4 or, to a lesser extent, between C‐2 and C‐3 due to the different migration aptitudes of the two acyl groups involved. In a cognate manner ring expansion between C‐2 and C‐3 occured by the interaction of diazomethane and the pyrrolidinetrione hydrazone 15 , to give the spiroe‐poxide 16 as the final product. From the reaction of trione 4 and diazomethane, however, the diepoxide 14 was obtained. In this case ring homologation must have taken place by insertion of carbon between C‐4 and C‐5. In a two step ring expansion the pyridones 21 and 22 were obtained from the maleineimides 17. 相似文献
997.
David J. Penfold Kurt Pike Anthony Genge Mike Anson John Kitteringham Jeremy D. Kilburn 《Tetrahedron letters》2000,41(52):10347-10351
Addition of lithium bis(methylenecyclopropyl)cuprates to acetoxy azetidinones gives methylenecyclopropyl azetidinones, which can be converted to various radical cyclisation precursors. Attempted 4-exo cyclisation of 3 led only to reduced product, while cyclisation of 5, using CuCl/bipy, gave a carbacephem, via a 5-exo cyclisation, but in low yield. Cyclisation of 6 and 7, however, gave novel tricyclic β-lactams, as the result of 7-endo cyclisation, in good yield, and a cyclisation of bromide 23 led to the tricyclic β-lactam 24, via a radical cascade sequence. 相似文献
998.
Daniel T. Seidenkranz Kurt A. Langworthy Lev N. Zakharov 《Supramolecular chemistry》2019,31(8):499-507
ABSTRACTWe report here the first chiral barbiturate to act as a single-component LMOG capable of gelating a variety of chlorinated and aromatic solvents. Solution-based DOSY NMR experiments, solid-state VP-SEM, and X-ray crystallography techniques were used to characterize chloroform-based gels at a variety of size domains. This scaffold provides a simple system to study the dynamics of gelation and self-assembly. 相似文献
999.
Treatment of molybdenum(II) acetate with thioether functionalized silylamides R2Si(NLi-C6H4–2-SR')2 leads to the formation of dinuclear MoII complexes [Mo2{R2Si(NC6H4-2-SR')2}2]. According to X-ray crystal structure analyses the complexes [Mo2{Me2Si(NC6H4-2-SMe)2}2] and [Mo2{Ph2Si(NC6H4-2-SPh)2}2] comprise a Mo2-unit which is coordinated by two μ-κ-N,N' silylamide ligands. The coordination sphere around the molybdenum atoms consists of two amide nitrogen atoms and two thioether sulfur atoms in a distorted square-planar arrangement. The Mo-Mo distances are 211.0(1) and 211.7(1) pm, resp. In the complex [Mo2{Ph2Si(NC6H4-2-SMe)2}2] the silyl amide units act as tetradentate κ-N,N',S,S'chelating ligands and the Mo-Mo distance is 218.6(1) pm. 相似文献
1000.
Fluorite-related ceramics have attracted considerable attention as potential host materials for the immobilisation of radionuclides. Here we have used computer simulation to investigate the relative solution energies and mechanisms for Pu3+, Pu4+ and U4+ accommodation in an extensive range of A2B2O7 pyrochlore compounds. Solution is considered from simple oxides and via co-solution mechanisms. Results are discussed in terms of their implications for actinide retention and materials fabrication. 相似文献