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941.
The allylic amination of unfunctionalyzed olefins by nitroarenes under CO pressure, catalyzed by Ru3(CO)12/Ph-BIAN (Ph-BIAN=bis(phenylimino)acenaphthenequinone) has been extended to some substrates with strongly electron-withdrawing groups on the nitroarene. Reaction of 1,4-dinitrobenzene selectively affords functionalization of only one nitro group, the other remaining unreacted. However, the second nitro group can be reduced in one pot by CO/H2O in the presence of the same catalytic system employed in the amination reaction, to afford the corresponding 4-amino derivative. Some attempts to render the reaction enantioselective by employing chiral bis-oxazolines as ligands in place of Ph-BIAN are described. Bis-oxazolines are suitable ligands for the reaction, although not as efficient as Ph-BIAN, but the allylic amine obtained was found to be racemic. 相似文献
942.
943.
Alexander Argyros Sergio G. Leon-Saval Martijn A. van Eijkelenborg 《Optics Communications》2009,282(9):1785-1788
Twin-hollow-core microstructured optical fibres have been fabricated and characterised for the first time. The fibre cladding structure results in guidance by the inhibited coupling mechanism, in which there is a low overlap between the core modes and surrounding structure. This results in minimal interaction between the modes of each core in the transmission bands of the fibre and hence minimal coupling between the cores. It is shown that light is able to couple between the cores via coupling to cladding struts in the high loss wavelength bands. 相似文献
944.
Mauricio C. de Souza Carlos R.V. de Carvalho Wellington B. Brizon 《European Journal of Operational Research》2008
We treat a practical application of packing problems in feeding assembly lines. This study was motivated by a real situation encountered in the shop floor of a major automobile industry plant in Brazil. The assembly line feed problem (LFP) consists in how pack the items in the available containers to meet the line work centers’ requirements with a minimum total cost over the planning horizon. LFP is a variable-sized bin packing problem that has two special features: (i) a cardinality constraint on each bin’s size; and, (ii) a cost structure such that each bin’s cost varies according to the items that are packed in it. We propose an integer programming model and a GRASP heuristic for LFP. Numerical results on real-life test instances are reported. 相似文献
945.
946.
Hansford KA Perez Guarin SA Skene WG Lubell WD 《The Journal of organic chemistry》2005,70(20):7996-8000
[Chemical reaction: See text] A practical three-step synthesis of bis(pyrrol-2-yl)arylenes has been accomplished, featuring a copper-catalyzed tandem bidirectional addition of vinylmagnesium bromide to aryldicarboxylates. Spectroscopic and cyclic voltammetric analyses revealed the influence of the central aromatic core and pyrrole substitution pattern on the electrochemical properties of these comonomers. 相似文献
947.
Ennas Guido Marongiu Giaime Marras Sergio Piccaluga Giorgio 《Journal of nanoparticle research》2004,6(1):99-105
CoFe2O4–SiO2 and Fe–Co alloy–SiO2 nanocomposites were prepared by high energy ball milling of Si, -Fe2O3, Co3O4 and SiO2 mixtures, followed by thermal treatment under appropriate oxidative/reductive conditions. XRD and TEM measurements carried out after 50 h of milling show highly dispersed unidentified reaction products. Further thermal treatment at 900°C in air leads to spherical CoFe2O4 nanocrystals (NCs) with a narrow size distribution centered around 2.5 nm, uniformly dispersed in the amorphous SiO2 matrix. Reduction of this sample in a H2 flow at 800°C produces a mixture of dispersed metallic cobalt and iron silicate with traces of Fe–Co alloy NCs. Reduction of the as-milled sample, on the contrary, leads almost completely to Fe–Co alloy NCs uniformly dispersed in the SiO2 matrix and with an average particles size around 11.2 nm. 相似文献
948.
Lamberti C Groppo E Prestipino C Casassa S Ferrari AM Pisani C Giovanardi C Luches P Valeri S Boscherini F 《Physical review letters》2003,91(4):046101
Geometric parameters of NiO films epitaxially grown on Ag(001) were determined using two independent experimental techniques and ab initio simulations. Primary beam diffraction modulated electron emission experiments determined that the NiO films grow with O on top of Ag and that the oxide/metal interface distance is d=2.3+/-0.1 A. Polarization-dependent x-ray absorption, at the Ni-K edge, determined the tetragonal strain (r( parallel )=2.046+/-0.009 A, r( perpendicular )=2.12+/-0.02 A) and d=2.37+/-0.05 A. Periodic slab model results agree with the experiments (d=2.40, r( parallel )=2.07, r( perpendicular )=2.10 A; the O-on-top configuration is the most stable). 相似文献
949.
950.
The nonlinear dynamics of an inviscid magnetohydrodynamic system in a low-beta plasma is investigated through a simplified model obtained by a Galerkin projection. We show that a single Fourier mode dominates over the whole energy spectrum, a self-organization mechanism of turbulence being responsible for this nonlinear effect. Our results are in agreement with observations of an analogous phenomenon, say, the emergence of a quasi-single-helicity state both in numerical simulations and real experiments in reversed field pinch laboratory plasmas. 相似文献