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排序方式: 共有168条查询结果,搜索用时 28 毫秒
61.
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63.
M. Andersson Chr. Bargholtz Kj. Fransson E. Fumero L. Gerén L. Holmberg K. Lindh L. Mårtensson I. Sitnikova P. -E. Tegnér G. Weiss K. Wilhelmsen Rolander 《Physics of Atomic Nuclei》2002,65(4):628-629
The halo nucleus 6He has been studied in a pionic fusion experiment at the CELSIUS storage ring facility in Uppsala. The 6He nuclei were produced in reactions with a deuteron beam incident on a 4He jet target 0.9–5.4 MeV above threshold in the center-of-mass frame. The 6He ions were detected in a ΔE-E solid-state detector telescope inserted into the CELSIUS ring. The aim of the experiment was to investigate, in particular, the high-momentum part of the halo wave function by measuring the total and differential cross sections of the reaction d+4He→6He+π +. 相似文献
64.
The manufacturing of composite materials has gained momentum in Taiwan, the Republic of China, over recent years. Fiber-reinforced plastics (FRP) pressure vessels have been made successfully by filament winding. Reviewed in this work are the design consideration manufacturing technology and inspection procedure. This involves theoretical analysis, material selection, mandrel design, tooling, processing know-how and proof tests. 相似文献
65.
Summary Compounds with the composition CuXL, in which X=Cl– or Br– and L=R,S-1-amino-2-propanol andS-1-amino-2-propanol, both with deprotonated hydroxy groups, are described. Magnetic measurements strongly suggest these compounds to have a tetrameric cubane-type structure with a Cu4O4 core. The racemic and optically-active compounds show a different magnetic behaviour, most likely originating from different cluster types for the isomers. The results of the i.r., f.i.r. and e.s.r. spectra are in good agreement with the proposed cluster types. 相似文献
66.
Koole R Liljeroth P Oosterhout S Vanmaekelbergh D 《The journal of physical chemistry. B》2005,109(19):9205-9208
The Ti/TiO2/Au junction forms the basis of a promising new type of photovoltaic cell, provided that a light-harvesting antenna layer can be deposited on the thin gold film. We report that the electrical diode characteristics of the TiO2/Au Schottky barrier deteriorate by deposition of a hydrophobic quantum dot film, Merbromin dye adsorption, or electron-hole photogeneration in TiO2 under inert conditions. In the presence of oxygen and water vapor, the Schottky barrier characteristics and high photovoltage are recovered. The strong influence of the TiO2 surface chemistry on the (photo)electrical characteristics of the solar cell is discussed on the basis of an existing microscopic model. 相似文献
67.
Patrick J. Baesjou Willem L. Driessen Ger Challa Jan Reedijk 《Journal of molecular catalysis. A, Chemical》1996,110(3):195-210
The complex of copper(II) nitrate with N-methylimidazole (Nmiz) ligand has been studied as a catalyst for the oxidative coupling of 2,6-dimethylphenol by means of kinetic and spectroscopic measurements. The order of the reaction in copper is fractional and depends on the N/Cu ratio and the base/Cu ratio, indicating that there are at least two possible rate-determining steps, i.e. the formation of a dinuclear copper species and the phenol oxidation. EPR spectroscopy performed on frozen solutions with varying ligand to copper ratios shows that all Cu(II) is converted into the precursor complex at a ratio of 4 to 1, whereas in kinetic experiments, maximum activity and selectivity are reached only at a ratio of at least 30 to 1. Base is needed as a co-catalyst, and the maximum reaction rate is reached at a base to copper ratio of 1.8 to 1. The solid-state X-ray structure of the catalyst precursor complex has been determined to be [Cu(Nmiz)4(NO3)2], monoclinic, space group P21/n, a = 8.452(1) Å, b = 10.376(2)Å, c = 12.821(2)Å, β = 94.88(2) °, Z = 1, R = 0.049 for 3525 reflections. This structure consists of an axially elongated octahedral CuN4O2 chromophore, which is in agreement with frozen-solution EPR spectra. Investigations under conditions where water and dioxygen were carefully excluded, have shown that for the phenol oxidation step the presence of dioxygen is not required. However, the reaction does require a trace of water (or hydroxide) to form the reactive intermediate. A modified reaction mechanism for the oxidative coupling is presented with special attention to the first steps of the reaction and the equilibrium species present in solution. The role of dioxygen appears to be only to reoxidize the formed Cu(I) species and to regenerate base. 相似文献
68.
Jan P. C. Bootsma Leo A. M. Rupert Ger Challa Franz Müller 《Journal of polymer science. Part A, Polymer chemistry》1984,22(9):2169-2180
The strong influence of medium composition (water/2-propanol mixtures) on the rate of oxidation of 1-substituted dihydronicotinamides by a flavin-containing polyelectrolyte was studied. We found that the coil dimensions of the corresponding copolymer of styrene and vinylbenzyltriethylammoniumchloride without flavin groups dramatically depend on the solvent. Viscometric measurements revealed compact coil conformations in solvents of both high water and high 2-propanol content, but pronounced coil expansion in intermediate mixtures. These changes of polyelectrolyte coil dimensions are related to changes in electrostatic potential of the microreactors. Addition of 2-propanol also results in decrease of substrate enrichments, caused by weakening of nonpolar polymer–substrate interactions, as was demonstrated for 1-carbamoylmethyl-, 1-benzyl-, and 1 decyl-substituted 1,4-dihydronicotinamide substrates. The enormous decrease in rate constant for oxidation of DNAH by 2 upon increasing the 2-propanol content from 10 to 40% (v/v), from k = 3120 to 21 M?1 s?1, can thus be explained as a cooperation of both effects. Evidence for the formation of a charge transfer complex between the polyelectrolyte-bound flavin and the dihydronicotinamide having a long-wavelength absorption is also presented. 相似文献
69.
A J Coenen L H Henckens Y Mengerink S van der Wal P J Quaedflieg L H Koole E M Meijer 《Journal of chromatography. A》1992,596(1):59-66
The separation by reversed-phase high-performance liquid chromatography of Rp and Sp diastereomers of phosphate-methylated DNA and RNA dinucleotides was studied with respect to pH, organic modifier type and concentration and reversed-phase packing material. Drylab G was used to deduce optimum conditions. On the basis of the observed discrepancies between the computer predictions and experimental results, the gradient operation procedure with volatile buffers was improved. By repetitive chromatography on a 250 x 22 mm I.D. reversed-phase column, fourteen diastereomeric pairs were obtained in at least 97% purity and 60% yield, in amounts of 10-100 mg. 相似文献
70.