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In this paper we outline a new particle-mesh method for rapidly rotating shallow water flows based on a set of regularized equations of motion. The time-stepping method uses an operator splitting of the equations into an Eulerian gravity wave part and a Lagrangian advection part. An essential ingredient is the advection of absolute vorticity by means of translated radial basis functions. We show that this implies exact conservation of enstrophy. The method is tested on two model problems based on the qualitative features of the solutions obtained (i.e., dispersion or smoothness of potential vorticity contours) as well as on the increase in mean divergence level. 相似文献
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Francis J. Narcowich Joseph D. Ward Holger Wendland. 《Mathematics of Computation》2005,74(250):743-763
In this paper we discuss Sobolev bounds on functions that vanish at scattered points in a bounded, Lipschitz domain that satisfies a uniform interior cone condition. The Sobolev spaces involved may have fractional as well as integer order. We then apply these results to obtain estimates for continuous and discrete least squares surface fits via radial basis functions (RBFs). These estimates include situations in which the target function does not belong to the native space of the RBF.
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Langer P Armbrust H Eckardt T Magull J 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(6):1443-1455
The Lewis acid mediated cyclization of epoxides with 1,3-bis(trimethylsilyloxy)-1,3-butadienes, electroneutral equivalents of 1,3-dicarbonyl dianions, results in the formation of 2-alkylidenetetrahydrofurans with a great variety of substitution patterns and functional groups. This includes the synthesis of 2,3'-bifuranylidenes and 7-oxabicyclo[4.3.0]nonanes. The cyclization of dienes with functionalized epoxides containing base-labile groups proceeds with good chemoselectivity. In all reactions, good regio- and E diastereoselectivities are observed. Based on the stereoselectivities observed for reactions of 1,2-disubstituted epoxides, a working hypothesis for the mechanism of the reaction is suggested. 相似文献
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The synthesis of two new aromatic cyclic enediynes 1a and 1b using a double Wittig condensation, followed by bromination and di-dehydrobromination, is reported. The structures were determined using X-ray crystallography. The observed C(1)-C(6) distances of the enediyne moiety in the oxygen- and sulfur-containing eleven-membered rings are quite short with 3.44 and 3.50 A, respectively, indicating the highly strained nature of these compounds. Isodesmic calculations at the B3LYP/6-31G level of theory indicate a strain energy of 8.2 and 5.8 kcal/mol, respectively. Despite the highly strained ring system, the compounds were found to be stable under thermal, photochemical, and electron-transfer conditions. Using BLYP/6-311+G/BLYP/6-31G calculations, the origin of this unusual stability was traced to the high energy of the 1,4 benzyne diradicals formed via Bergman cyclization. For the radical cation, both the C(1)-C(6) and the C(1)-C(5) cyclization mode previously reported for acyclic analogues of 1 were found to be energetically prohibitive. 相似文献