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排序方式: 共有157条查询结果,搜索用时 31 毫秒
41.
A combination of HBr and trans-3,5-dihydroperoxy-3,5-dimethyl-1,2-dioxolane as anew and powerful oxidant was found effective for facile brotnination of different aromatic compounds at room temperature in water as a green solvent.Mild reaction conditions,high selectivity and yield,high reaction rate and non-toxicity are some of the major advantages of this synthetic protocol. 相似文献
42.
43.
Building on the recent axiomatisation of infinite matroids with duality, we present a theory of representability for infinite matroids. This notion of representability allows for infinite sums, and is preserved under duality. 相似文献
44.
45.
Measurements of the thermal desorption of methyl bromide (MeBr) from bare and RS-functionalized GaAs(110), where R = CH3 and CH3CH2, reveal marked systematic changes in molecule-surface interactions. As the thickness of the organic spacer layer is increased, the electrostatic MeBr-GaAs(110) interaction decreases, lowering the activation energy for desorption, Ed, as well as decreasing the critical coverage required for nucleation of bulklike MeBr. On the CH3CH2S-functionalized surface, Ed is lowered to a value roughly equal to that for desorption from three-dimensional (3-D) clusters; because the kinetics of desorption of isolated molecules differs from that for desorption from clusters, desorption of isolated molecules from the organic surface occurs at a lower temperature than desorption from the clusters. Thus, the "monolayer" desorption wave occurs at a lower temperature than the "multilayer" desorption wave. These results illustrate the role that organic chain length in nanometer-scale thin films can play in alteration of the delicate balance of interfacial interactions. 相似文献
46.
Summary: In this work, a surface re-modified multi-walled carbon nanotube (MWNT) was prepared by the chemical attachment of oligomeric unsaturated polyester on the MWNT surface. The re-modified MWNT was incorporated in two concentrations of 0.35 and 0.70 Wt.% into epoxy resin in order to investigate its effect on morphology and mechanical behavior of the MWNT/epoxy nanocomposite. The transmission electron microscopy showed that the re-modification of MWNT surface improves its dispersion state in the epoxy matrix. The tensile measurements for the nanocomposite having different amounts of surface re-modified/not-modified MWNT showed that the fracture mechanism changed from brittle to tough beyond a certain amount of surface re-modified MWNT. The scanning electron microscopy findings on the fracture surface morphology of the resulted nanocomposite substantiated the observed phenomena. 相似文献
47.
Kaveh Parvanak Boroujeni 《中国化学快报》2010,21(12):1395-1398
<正>Silica gel supported aluminium trichloride(SiO_2-AlCl_3) has been shown to be a mild,efficient,and chemoseiective heterogeneous Lewis acid catalyst for the acylation of aromatic compounds with acid chlorides.The catalyst can be reused up to five times after simple washing with ether and is stable(as a bench top catalyst). 相似文献
48.
E. Kogan M. Auslender M. Kaveh 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,9(3):373-376
Localization and dephasing of conduction electrons in a low carrier density ferromagnet due to scattering on magnetic fluctuations
is considered. We claim the existence of the “mobility edge”, which separates the states with fast diffusion and the states
with slow diffusion; the latter is determined by the dephasing time. When the “mobility edge” crosses the Fermi energy a large
and sharp change of conductivity is observed. The theory provides an explanation for the observed temperature dependence of
conductivity in ferromagnetic semiconductors and manganite pyrochlores.
Received 17 January 1999 and Received in final form 12 March 1999 相似文献
49.
In this paper an efficient method is developed for decomposing large-scale finite element meshes. A weighted incidence graph is used to transform the connectivity properties of finite element models into those of graphs. A graph Gc of manageable size is obtained from the main graph model by a coarsening algorithm. The p-medians of this graph are selected using two approaches. The first algorithm uses an ant colony optimization and the second algorithm employs a hybrid ant colony together with genetic algorithm. Here, p is the number of subdomains which the finite element meshes is intended to be decomposed. Once the medians are obtained, the nodes in Gc associated with each median are selected. In an expansion process, the nodes of the subdomains in G are obtained. The capabilities of both ant colony optimization, and hybrid ant colony and genetic algorithm are evaluated using many examples of different topology. 相似文献
50.
We present a review of part of the results obtained by the authors for the statistics of coherent radiation propagating in a random medium both in the framework of diagrammatic techniques and random matrix theory. Distribution functions for the total transmission coefficient and the angular transmission coefficient for the diffusive transport and the crossover between the diffusive and ballistic regimes are obtained.The authors acknowledge the financial support of the Israeli Academy of Sciences and of the Schottenstein Center. 相似文献