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51.
Vermoortele F Ameloot R Vimont A Serre C De Vos D 《Chemical communications (Cambridge, England)》2011,47(5):1521-1523
After controlled pretreatment, some Zr-terephthalate metal-organic frameworks are highly selective catalysts for the cross-aldol condensation between benzaldehyde and heptanal. The proximity of Lewis acid and base sites in the amino-functionalized UiO-66(NH(2)) material further raises the reaction yields. 相似文献
52.
Peeters A Valvekens P Vermoortele F Ameloot R Kirschhock C De Vos D 《Chemical communications (Cambridge, England)》2011,47(14):4114-4116
Double metal cyanides (DMCs) are highly active recyclable heterogeneous catalysts for hydroamination of phenylacetylene with 4-isopropylaniline. The best hydroamination yields are obtained with Zn-Co DMCs, especially if the particle size is decreased by a reverse emulsion synthesis technique. 相似文献
53.
The frequency dependence of the double-layer capacitance has been studied at the interface Hg/0.116 M KCl in water at ?1.200 V vs. a reversible calomel electrode at 25°C. Two drop electrodes attached to 0.1-mm platinum wire have been used, one sessile with a narrow wedge, the other pendant with a widely open wedge between drop surface and support. The operation of the a.c. resistor-ratio arms bridge has been analysed in a manner generally applicable to series-R, C measurements. On that basis the effect of stray capacitances could be compensated and the frequency dispersion due to the measuring system reduced to a minimum. Both electrodes show a low-frequency dispersion of the measured series capacitance C(ω) and resistance R(ω), ω being the angular frequency. This dispersion has been analysed with a simple R, C network. In series with the bulk resistance R3 this network has two mutually parallel series R, C's: R1, C1 of the drop itself and R2, C2 of its edge (neck). From the actual C(ω), R(ω) data follow correct capacitance data C1, while R2 and C2 show a relatively stronger dependence on frequency and kind of electrode (pendant or sessile). Moreover, a sessile electrode exhibits a wedge or shielding effect above a much smaller ω (=ωh >ω1, the frequency above which the edge effect becomes insignificant) than a pendant electrode. Conclusions drawn from this information are: in the frequency domain (ωh?ω1) diffusive mass transport may be studied without interference from any geometric effect, which is probably also true at small electrolyte concentrations. This study should be performed with a pendant electrode, since it has the largest (ωh?ω1) domain. 相似文献
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Recent photoemission experiments have measured E vs. k for a single hole propagating in antiferromagnetically aligned Sr2CuO2Cl2. Comparisons with (i) the t - t′ - J model, for which the carrier is a spinless vacancy, and (ii) a strong-coupling version of the three-band Emery model, for which the carrier is a S = 1/2 hole moving on the Oxygen sublattice, have demonstrated that if one wishes to describe the quasiparticle throughout the entire first Brillouin zone the three-band model is superior. Here we present a new variational wave function for a single Oxygen hole in the three-band model: it utilizes a classical representation of the antiferromagnetically ordered Cuspin background but explicitly includes the quantum fluctuations of the lowest energy doublet of the Cu-O-Cu bond containing the Oxygen hole. We find that this wave function leads to a quasiparticle dispersion for physical exchange and hopping parameters that is in excellent agreement with the measured ARPES data. We also obtain the average spin of the Oxygen hole, and thus deduce that this spin is only quenched to zero at certain wave vectors, helping to explain the inadequacy of the t - t′ - J model to match the experimentally observed dispersion relation everywhere in the first Brillouin zone. 相似文献
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M. Vos G.A. Sawatzky M. Davies P. Weightman P.T. Andrews 《Solid State Communications》1984,52(2):159-162
We show that the local impurity density of states and the impurity electron—electron interactions can be obtained from impurity Auger spectra. For a Ag0.95Pd0.05 alloy we find 11% Pd(d) character in the Ag d band and Pd(4d-4d) Coulomb interactions which are much larger than the virtual bound state widths. 相似文献
60.
Hubert G. Theuns Guus F. La Vos Michael C. ten Noever de Brauw Cornelis A. Salemink 《Tetrahedron letters》1984,25(37):4161-4162
Photochemical irradiation of the morphinan alkaloid thebaine 1 followed by reduction, affords the dibenz[d,f]azonine alkaloids neodihydrothebaine 2 and bractazonine 3, in a sequence paralleling the proposed biosynthesis of these alkaloids in Papaver bracteatum. 相似文献