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41.
The reaction of aryl iodides and bromides with acrolein diethyl acetal in the presence of Pd(OAc)(2), (n)()Bu(4)NOAc, K(2)CO(3), KCl, and DMF, at 90 degrees C until the disappearance of the acetal followed by the addition of 2 N HCl to the crude reaction mixture, affords cinnamaldehydes in good to high yields. A variety of functional groups are tolerated in the aryl halides, including ether, aldehyde, ketone, ester, dialkylamino, nitrile, and nitro groups. The presence of substituents close to the oxidative addition site does not hamper the reaction. 相似文献
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We investigate the effects of delaying the time to recovery (delayed recovery) and of nonuniform transmission on the propagation of diseases on structured populations. Through a mean-field approximation and large-scale numerical simulations, we find that postponing the transition from the infectious to the recovered states can largely reduce the epidemic threshold, therefore promoting the outbreak of epidemics. On the other hand, if we consider nonuniform transmission among individuals, the epidemic threshold increases, thus inhibiting the spreading process. When both mechanisms are at work, the latter might prevail, hence resulting in an increase of the epidemic threshold with respect to the standard case, in which both ingredients are absent. Our findings are of interest for a better understanding of how diseases propagate on structured populations and to a further design of efficient immunization strategies. 相似文献
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N-Propargylic beta-enaminones have been used as common intermediates for the synthesis of polysubstituted pyrroles and pyridines. Best results have been obtained using DMSO as solvent. In the presence of Cs(2)CO(3) N-propargylic beta-enaminones are cyclized to pyrroles in good to high yields, whereas omitting bases and using CuBr leads to the selective formation of pyridines. 相似文献
47.
Maria Rosa M. L. Albuquerque Gilcarlos R. Medeiros Sandro J. F. Oliveira Adaildo G. dAssunção 《International Journal of Infrared and Millimeter Waves》2005,26(6):855-866
The design of nonuniform bilateral finlines on anisotropic substrates for millimeter wave applications is presented. The taper consists of a planar circuit with smooth variation of the slot width profile along the structure. The spectral domain method and Galerkin procedure are combined with the transmission line theory for studying the behavior of tapered bilateral finlines and evaluation of their design parameters. The influence of the substrate anisotropy on the propagation characteristics of these structures is also examined. This technique is general and can be applied to investigate a broad class of planar transmission line tapers. 相似文献
48.
Sandro Faedo 《Annali di Matematica Pura ed Applicata》1897,25(1):111-133
Sunto Estendendo e approfondendo classiche ricerche diM. B?cher eU. Dini si dimostra che un'equazione differenziale lineare omogenea d'ordinen, i cui coefficienti sono funzioni quasi continue che soddisfano a opportune condizioni di sommabilità, possiede nell' intorno
di un punto singolare (in cui le dette condizioni non sono verificate) un sistema fondamentale d'integrali che si calcolano
esplicitamente mediante serie derivabili termine a terminen−1 volte. Si confrontano i risultati con quelli ottenuti daFuchs per le equazioni a coefficienti analitici e se ne fa applicazione alla ricerca delle proprietà asintotiche delle soluzioni
di una equazione differenziale lineare omogenea d'ordinen.
Questa Memorta è già apparsa litografata nel 1946 presso la litografia D. Tacchi & F., Pisa. 相似文献
49.
A combination of more stable counter-cation (tetraphenylphosphonium in place of tetrapropylammonium), of local basic microenvironment, and of a non-solubilizing reaction medium (supercritical CO2) improves the life-cycle and reusability of catalytic ORMOSILs doped with perruthenate in the oxidation of alcohols with O2. A number of different bases were co-entrapped and their effect on catalysis assessed in the oxidative dehydrogenation of benzyl alcohol in dense phase carbon dioxide at 22 MPa and 75 °C. The optimized catalyst retains most of its activity after five consecutive runs when a normal ORMOSIL-entrapped TPAP has become inactive. Deactivation of TPAP could be ascribed by EPR analysis to the formation of catalytically inactive RuO2. 相似文献
50.
Frank Langhans Stefan Kiefer Carsten Hartmann Toni Markurt Tobias Schulz Christo Guguschev Martin Naumann Sandro Kollowa Andrea Dittmar Jürgen Wollweber Matthias Bickermann 《Crystal Research and Technology》2016,51(2):129-136
In order to evaluate the possible involvement of crucible materials in the growth of AlN bulk crystals grown by physical vapor transport, we applied growth conditions with a high vertical thermal gradient and hence high supersaturation of aluminum vapor. Under these conditions, precipitates formed causing diffuse grayish substructures at the initial growth interface and in the crystal body, decorating dislocations. Electron microscopy studies revealed that the precipitates are elongated, single‐phase particles with sizes of 50–500 nm of commensurate structure, oriented along the <110> direction. Chemical analysis of the precipitates showed tungsten as well as carbon and oxygen. The lattice parameters of the precipitates are in close agreement to hexagonal tungsten hemicarbide (W2C). The possible transport from the tungsten parts and its conversion into tungsten hemicarbide precipitates is discussed. We thus conclude that the W2C precipitates may contribute to the decoration of dislocations, even in growth with moderate thermal gradients. 相似文献