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91.
Given a polygonal path P with vertices and a real number , a path is a t-distance-preserving approximation of P if and each straight-line edge of Q approximates the distance between and along the path P within a factor of t. We present exact and approximation algorithms that compute such a path Q that minimizes k (when given t) or t (when given k). We also present some experimental results. 相似文献
92.
Andrei M Bjørnstad V Langli G Rømming C Klaveness J Taskén K Undheim K 《Organic & biomolecular chemistry》2007,5(13):2070-2080
Cyclic adenosine monophosphate (cAMP) has been converted into its 8-bromo derivative and 2'O-TBDMS protected before activation of the phosphoric acid moiety with a reagent generated in situ from oxalyl chloride and DMF. Further reactions with primary amines furnished corresponding phosphoramidates with high stereoselectivity at the phosphorus atom. Cross-coupling reactions with the 8-bromopurine yielded 8-hetaryl derivatives. X-Ray analyses showed the amidates to possess the (S(P))-configuration. Carbon disulfide effected thiylation under strongly basic conditions stereospecifically provided the (R(P))-phosphorothioic acids. 相似文献
93.
The velocities of Ar+ and Xe+ ions near the presheath-sheath boundary in an Ar/Xe discharge are studied by particle-in-cell Monte Carlo simulation. For a pure argon discharge the argon ion has almost the same velocity profile as it does in the mixture of argon and xenon. Similarly, for a xenon discharge the xenon ion has almost the same velocity profile as it does in the mixture of argon and xenon. The ion speed at the sheath-presheath boundary is the same for an ion in a pure argon or xenon discharge and for the same ion in a mixture of argon and xenon. We conclude that, in our simulation, each ion reaches its own Bohm speed at the presheath-sheath interface. 相似文献
94.
Vidar Gudmundsson Sigtryggur Hauksson Arni Johnsen Gilbert Reinisch Andrei Manolescu Christophe Besse Guillaume Dujardin 《Annalen der Physik》2014,526(5-6):235-248
The recent results on the linear breathing mode of the excitation spectrum of a quantum dot obtained by McDonald et. al [Phys. Rev. Lett. 111 , 256801 (2013)] are extended to the nonlinear regime. To accomplish this and analyze the results the response of five different models of two interacting electrons in a quantum dot to an external short lived radial excitation that is strong enough to excite the system well beyond the linear response regime is compared. The models considered describe the Coulomb interaction between the electrons in different ways ranging from mean‐field approaches to configuration interaction (CI) models, where the two‐electron Hamiltonian is diagonalized in a large truncated Fock space. The radially symmetric excitation is selected in order to severely put to test the different approaches to describe the interaction and correlations of an electron system in a nonequilibrium state. As can be expected for the case of only two electrons none of the mean‐field models can in full details reproduce the results obtained by the CI model. Nonetheless, some linear and nonlinear characteristics are reproduced reasonably well. All the models show activation of an increasing number of collective modes as the strength of the excitation is increased. By varying slightly the confinement potential of the dot it was observed how sensitive the properties of the excitation spectrum are to the Coulomb interaction and its correlation effects. In order to approach closer the question of nonlinearity one of the mean‐field models has been solved directly in a nonlinear fashion without resorting to iterations. 相似文献
95.
Nikolai Yu. Bakaev Vidar Thomé e Lars B. Wahlbin. 《Mathematics of Computation》2003,72(244):1597-1610
Let be a convex domain with smooth boundary in . It has been shown recently that the semigroup generated by the discrete Laplacian for quasi-uniform families of piecewise linear finite element spaces on is analytic with respect to the maximum-norm, uniformly in the mesh-width. This implies a resolvent estimate of standard form in the maximum-norm outside some sector in the right halfplane, and conversely. Here we show directly that such a resolvent estimate holds outside any sector around the positive real axis, with arbitrarily small angle. This is useful in the study of fully discrete approximations based on -stable rational functions, with small.
96.
97.
98.
Synthesis of juniperonic acid [(all-Z)-5,11,14,17-eicosatetraenoic acid], has been achieved in eight steps and in 19% overall yield starting from eicosapentaenoic acid. 相似文献
99.
We present a new and simple (1+ε)-spanner of size O(n/ε2) for a set of n points in the plane, which can be maintained efficiently as the points move. Assuming the trajectories of the points can be described by polynomials whose degrees are at most s, the number of topological changes to the spanner is O((n/ε2)λs+2(n)), and at each event the spanner can be updated in O(1) time. 相似文献
100.
Polychlorinated imidazo[1,2-α]pyridines were synthesized as analogs of certain chlorinated benzimidazoles. The imidazo[1,2-α]pyridines were obtained by a condensation of ethyl bromoacetate and chlorinated 2-aminopyridines. These condensation products were treated with an ion exchange resin to effect an exchange of hydrobromide salts with hydrochloride salts. These compounds were subsequently treated with POCl3 to convert the imidazo[1,2-α]pyridin-2-ones into 2-chloroimidazo[1,2-a]pyridines. 相似文献