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911.
Imidazolium-tagged ferrocenyl diphosphanes are useful ligands in palladium-catalyzed allylic substitutions with heteroatom nucleophiles. Substitution with phthalimide proceeds with high enantioselectivity (up to 92% ee) in various ionic liquids. Reaction with p-cresol as nucleophile affords allylation product in up to 62% ee, while using tolylsulfinate as a nucleophile gives a product with very little or no enantioselectivity. Under these reaction conditions, catalyst recyclability is challenging, and decrease in activity as well as enantioselectivity was observed. 相似文献
912.
Ohne Zusammenfassung 相似文献
913.
A new low-temperature plasma surface modification of advanced polyester tire cord at atmospheric pressure was tested. Plasma surface treatment was performed in the barrier discharge plasmas (BDPs, atmospheric pressure glow discharge (APG) and plasma of gliding are (Glid Arc). The surface properties were characterized by the electron spin resonance spectroscopy (ESR), measurements of the contact angle of various polar and non-polar liquids with polyester cords, H-test, peel test and partially by zeta potential measurements. Further tests have been performed at an industrial testingimpregnation line where the common technology was applied on both plasma treated and untreated fibres. The standard H-test and peel-tests were used to characterize the adhesion of the fibre to usual testingrubbers. 相似文献
914.
915.
J. Török S. Krishnamurthy J. Kertész S. Roux 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,18(4):697-701
We introduce a model for the slow relaxation of an energy landscape caused by its local interaction with a random walker whose
motion is dictated by the landscape itself. By choosing relevant measures of time and potential this self-quenched dynamics can be mapped on to the “True” Self-Avoiding Walk model. This correspondence reveals that the average distance of
the walker at time t from its starting point is , where for one dimension and 1/2 for all higher dimensions. Furthermore, the evolution of the landscape is similar to that in growth
models with extremal dynamics.
Received 8 August 2000 相似文献
916.
We show that the conjectures by Matthews and Sumner (every 4-connected claw-free graph is Hamiltonian), by Thomassen (every 4-connected line graph is Hamiltonian) and by Fleischner (every cyclically 4-edge-connected cubic graph has either a 3-edge-coloring or a dominating cycle), which are known to be equivalent, are equivalent to the statement that every snark (i.e. a cyclically 4-edge-connected cubic graph of girth at least five that is not 3-edge-colorable) has a dominating cycle.We use a refinement of the contractibility technique which was introduced by Ryjá?ek and Schelp in 2003 as a common generalization and strengthening of the reduction techniques by Catlin and Veldman and of the closure concept introduced by Ryjá?ek in 1997. 相似文献
917.
Ohne Zusammenfassung 相似文献
918.
A k-uniform hypergraph is hamiltonian if for some cyclic ordering of its vertex set, every k consecutive vertices form an edge. In 1952 Dirac proved that if the minimum degree in an n-vertex graph is at least n/2 then the graph is hamiltonian.
We prove an approximate version of an analogous result for uniform hypergraphs: For every K ≥ 3 and γ > 0, and for all n large enough, a sufficient condition for an n-vertex k-uniform hypergraph to be hamiltonian is that each (k
− 1)-element set of vertices is contained in at least (1/2 + γ)n edges.
Research supported by NSF grant DMS-0300529.
Research supported by KBN grant 2P03A 015 23 and N201036 32/2546. Part of research performed at Emory University, Atlanta.
Research supported by NSF grant DMS-0100784. 相似文献
919.
920.