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11.
Abstract The Hetero Diels-Alder reaction of enamino ketones and ethyl vinyl ether to give dihydropyrans is studied in different solutions under pressure up to 7 kbar. The kinetics is measured via on-line FT IR spectroscopy. The cycloaddition shows a remarkable pressure dependent increase in diastereo-selectivity. For the difference in activation volumes referring to the reaction to the two diastereomers, values up to 5.9 ± 0.5 cm3/mol are observed. The ratio of cis and trans diastereomers can be improved by almost one order of magnitude by changing pressure and temperature from 1 bar and 90 °C to 6 kbar and 0.5 °C. 相似文献
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We discuss Gaussian generalized random fields indexed by smoothsections of vector bundles with respect to Markov properties.We propose a new set-up which is suitable for the present questionand within which new phenomena are detected naturally. In particular,we give a counterexample to the belief that locality in theRKHS implies the germ Markov property. We also prove the closeconnection between the Markov property and cokernels of localoperators. Furthermore, we prove the Markov property for a verydegenerate Gaussian random field. 相似文献
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G. Autie‐Castro M. Autie E. Reguera J. Santamaría‐González R. Moreno‐Tost E. Rodríguez‐Castellón A. Jiménez‐López 《Surface and interface analysis : SIA》2009,41(9):730-734
The adsorption and separation of light n‐alkane hydrocarbons (propane, butane, pentane, hexane and heptane) by zinc and cadmium hexacyanocobaltates (III) were studied from inverse gas chromatographic data. These two solids are representative of the porous frameworks found for transition metals hexacyanometallates. For cadmium, the porous framework is related to the presence of systematic vacancies for the building block, [Co(CN)6], while for Zn it is a consequence of a tetrahedral coordination for the Zn atom. These linear light hydrocarbons (paraffins) are effectively separated by these two porous frameworks. The involved differential adsorption heats and the related separation coefficients were estimated from the recorded chromatographic data. No significant differences for the separation ability of light n‐alkane hydrocarbons by the evaluated materials were observed. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
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Summary: Raman spectroscopy was applied to perform a comprehensive morphological analysis of polyethylene (PE) ski base materials at different processing levels. The morphological characterization included determination and evaluation of Raman spectra and examination of the crystallinity values by differential scanning calorimetry (DSC). A good agreement between Raman and DSC crystallinity fractions was obtained, thus corroborating the Raman spectroscopy approach. While for the PE grade with the lowest average molar mass no significant morphological changes due to processing from the raw material via the extruded film to the post-treated film was found, higher molar mass PE grades exhibited a decrease of crystallinity, but an increase of the amorphous fraction along the process chain. 相似文献
17.
Bing Shi Jon M. Hiller Yuzi Liu Chian Liu Jun Qian Lisa Gades Michael J. Wieczorek Albert T. Marander Jorg Maser Lahsen Assoufid 《Journal of synchrotron radiation》2012,19(3):425-427
X‐ray optics called multilayer Laue lenses (MLLs) provide a promising path to focusing hard X‐rays with high focusing efficiency at a resolution between 5 nm and 20 nm. MLLs consist of thousands of depth‐graded thin layers. The thickness of each layer obeys the linear zone plate law. X‐ray beamline tests have been performed on magnetron sputter‐deposited WSi2/Si MLLs at the Advanced Photon Source/Center for Nanoscale Materials 26‐ID nanoprobe beamline. However, it is still very challenging to accurately grow each layer at the designed thickness during deposition; errors introduced during thickness measurements of thousands of layers lead to inaccurate MLL structures. Here, a new metrology approach that can accurately measure thickness by introducing regular marks on the cross section of thousands of layers using a focused ion beam is reported. This new measurement method is compared with a previous method. More accurate results are obtained using the new measurement approach. 相似文献
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Tam NM Ngan VT de Haeck J Bhattacharyya S Le HT Janssens E Lievens P Nguyen MT 《The Journal of chemical physics》2012,136(2):024301
The geometric structures of neutral and cationic Si(n)Li(m)(0/+) clusters with n = 2-11 and m = 1, 2 are investigated using combined experimental and computational methods. The adiabatic ionization energy and vertical ionization energy (VIE) of Si(n)Li(m) clusters are determined using quantum chemical methods (B3LYP/6-311+G(d), G3B3, and CCSD(T)/aug-cc-pVxZ with x = D,T), whereas experimental values are derived from threshold photoionization experiments in the 4.68-6.24 eV range. Among the investigated cluster sizes, only Si(6)Li(2), Si(7)Li, Si(10)Li, and Si(11)Li have ionization thresholds below 6.24 eV and could be measured accurately. The ionization threshold and VIE obtained from the experimental photoionization efficiency curves agree well with the computed values. The growth mechanism of the lithium doped silicon clusters follows some simple rules: (1) neutral singly doped Si(n)Li clusters favor the Li atom addition on an edge or a face of the structure of the corresponding Si(n)(-) anion, while the cationic Si(n)Li(+) binds with one Si atom of the bare Si(n) cluster or adds on one of its edges, and (2) for doubly doped Si(n)Li(2)(0/+) clusters, the neutrals have the shape of the Si(n+1) counterparts with an additional Li atom added on an edge or a face of it, while the cations have both Li atoms added on edges or faces of the Si(n)(-) clusters. 相似文献
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We determine lattice polytopes of smallest volume with a given number of interior lattice points. We show that the Ehrhart
polynomials of those with one interior lattice point have largest roots with norm of order n2, where n is the dimension. This improves on the previously best known bound n and complements a recent result of Braun where
it is shown that the norm of a root of a Ehrhart polynomial is at most of order n2. For the class of 0-symmetric lattice polytopes we present a conjecture on the smallest volume for a given number of interior
lattice points and prove the conjecture for crosspolytopes. We further give a characterisation of the roots of Ehrhart polyomials
in the three-dimensional case and we classify for n ≤ 4 all lattice polytopes whose roots of their Ehrhart polynomials have
all real part -1/2. These polytopes belong to the class of reflexive polytopes. 相似文献