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排序方式: 共有335条查询结果,搜索用时 140 毫秒
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Suvi T.M. Orr Shawn CabralDilinie P. Fernando Teresa Makowski 《Tetrahedron letters》2011,52(28):3618-3620
A variety of chiral azetidinepiperidines have been synthesized utilizing an expedient one-pot union of piperidine chloroaldehyde with chiral amines. This two step one-pot procedure provides access to an interesting set of compounds that retain the chiral purity of the starting chiral amine. 相似文献
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This paper addresses the isomorphism problem for the universal (non-self-adjoint) operator algebras generated by a row contraction subject to homogeneous polynomial relations. We find that two such algebras are isometrically isomorphic if and only if the defining polynomial relations are the same up to a unitary change of variables, and that this happens if and only if the associated subproduct systems are isomorphic. The proof makes use of the complex analytic structure of the character space, together with some recent results on subproduct systems. Restricting attention to commutative operator algebras defined by a radical ideal of relations yields strong resemblances with classical algebraic geometry. These commutative operator algebras turn out to be algebras of analytic functions on algebraic varieties. We prove a projective Nullstellensatz connecting closed ideals and their zero sets. Under some technical assumptions, we find that two such algebras are isomorphic as algebras if and only if they are similar, and we obtain a clear geometrical picture of when this happens. This result is obtained with tools from algebraic geometry, reproducing kernel Hilbert spaces, and some new complex-geometric rigidity results of independent interest. The C?-envelopes of these algebras are also determined. The Banach-algebraic and the algebraic classification results are shown to hold for the wot-closures of these algebras as well. 相似文献
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Diana J. SchwerhaChun-Sing Orr Bean T. ChenSidney C. Soderholm 《Analytica chimica acta》2002,457(2):257-264
Photoacoustic Fourier transform-infrared spectroscopy (PA-FT-IR) has been used to perform direct-on-filter (DOF) analysis of crystalline silica using laboratory-generated filter samples. With these samples, the silica particles were embedded in the stable three-dimensional matrix of the filter. In this preliminary study, it was demonstrated that the photoacoustic (PA) signals generated from direct-on-filter measurements were significantly higher than the corresponding signals for equivalent amounts of silica particles placed directly in the photoacoustic detector cup. Studies with Min-U-Sil-5 loaded onto 9 mm filter stubs indicated a limit of detection of less than 10 μg. Additionally, Teflon filters were demonstrated to be more suitable for these measurements than other types. The photoacoustic FT-IR approach seems to be feasible for further development to use with full-sized personal sampling filters. 相似文献
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We study the concentration of adatoms on GaAs(001) during annealing under MBE conditions. By rapidly cooling the sample from typical growth temperatures and typical As overpressures, the thermal concentration of adatoms can be frozen into small islands on the terraces. The area of the resulting islands is measured with STM far from terrace steps, giving an estimate of the concentration of adatoms during equilibrium. We find that a surprisingly large concentration of adatoms is present for typical growth temperatures, e.g. 0.18 monolayer at 600°C. Possible consequences for current growth models are discussed. 相似文献
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R. Pfaff B. M. Young W. Benenson J. Clayton D. J. Morrissey N. A. Orr T. Reposeur M. Thoennessen J. A. Winger 《Zeitschrift für Physik A Hadrons and Nuclei》1993,347(1):67-70
A comparison has been made between the production of high energy (E γ≧30 MeV)γ rays from the bombardment of124Sn and112Sn targets withE/A= 10 MeV12C ions. The results are well explained by then-p bremsstrahlung model and do not indicate the need for any new processes. 相似文献
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J. F. Mc Clendon Th. v Fellenberg G. Pfeiffer L. Scheffer J. A. Höjer J. B. Orr W. Godden J. M. Dundas J. M. Kolthoff und K. Hillgruber 《Fresenius' Journal of Analytical Chemistry》1931,84(1-2):68-80
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