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921.
The diastereoselective synthesis of the macrolactone core of amphidinolide W was successfully accomplished using Evans’ asymmetric alkylation, Aldol reaction, Julia-Kocienski olefination, and Kita’s macrocyclization protocol. 相似文献
922.
923.
The dynamical behavior of multi-spot solutions in a two-dimensional domain Ω is analyzed for the two-component Schnakenburg
reaction–diffusion model in the singularly perturbed limit of small diffusivity ε for one of the two components. In the limit ε→0, a quasi-equilibrium spot pattern in the region away from the spots is constructed by representing each localized spot
as a logarithmic singularity of unknown strength S
j
for j=1,…,K at unknown spot locations x
j
∈Ω for j=1,…,K. A formal asymptotic analysis, which has the effect of summing infinite logarithmic series in powers of −1/log ε, is then used to derive an ODE differential algebraic system (DAE) for the collective coordinates S
j
and x
j
for j=1,…,K, which characterizes the slow dynamics of a spot pattern. This DAE system involves the Neumann Green’s function for the Laplacian.
By numerically examining the stability thresholds for a single spot solution, a specific criterion in terms of the source
strengths S
j
, for j=1,…,K, is then formulated to theoretically predict the initiation of a spot-splitting event. The analytical theory is illustrated
for spot patterns in the unit disk and the unit square, and is compared with full numerical results computed directly from
the Schnakenburg model.
相似文献
924.
A high‐order element‐based Galerkin method is developed to solve the non‐divergent barotropic vorticity equation (BVE). The solution process involves solving a conservative transport equation for the vorticity fields and a Poisson equation for the stream function fields. The discontinuous Galerkin method is employed for solving the transport equation and a spectral element method (continuous Galerkin) is used for the Poisson equation. A third‐order strong stability preserving explicit Runge–Kutta scheme is used for time integration. A series of tests have been performed to validate the model, which include the evolution of an idealized tropical cyclone and interaction of dual vortices in close proximity. The numerical convergence study is performed by solving the BVE on the sphere where the analytic solution is known. The test results are consistent with physical observations, and the model exhibits exponential convergence. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
925.
一个推广的具最佳常数的多参数Hardy-Hilbert不等式 总被引:2,自引:0,他引:2
刘琼 《数学的实践与认识》2008,38(2):127-132
引入λ1,λ2,α等多个参数,利用权系数方法,给出了一个推广的具最佳常数的多参数Hardy-Hilbert重级数不等式,并给出其等价形式. 相似文献
926.
Various authors have studied extensions of Shannon’s entropy but their inferential properties and applications in applied
sciences have not invited proper attention from researchers. In the present paper we explore the motivation and implication
of using various classes of the generalized entropies and conditional entropies. We evaluate β-class and (α, β)-class entropies for multivariate normal density function. We also obtain the measures of dependence in terms of the classes
of generalized entropies.
相似文献
927.
Aïssa Wade 《Annals of Global Analysis and Geometry》2008,33(3):207-217
Poisson fiber bundles are studied. We give sufficient conditions for the existence of a Dirac structure on the total space
of a Poisson fiber bundle endowed with a compatible connection. We also provide some examples.
相似文献
928.
We consider a two-level supply chain with a number of identical, independent ‘retailers’ at the lower echelon and a single supplier at the upper echelon controlled by continuous review inventory policy (R, Q). Each retailer experiences Poisson demand with constant transportation times. We assume constant lead time for replenishing supplier orders from an external warehouse to the supplier and unsatisfied retailer orders are backordered in the supplier. We assume that the unsatisfied demand is partially backordered in the identical retailers. The partially backordering policy is implemented in the identical retailers using an explicit control parameter ‘b’ which limits the maximum number of backorders allowed to be accumulated during the lead time. We develop an approximate cost function to find optimal reorder points for given batch sizes in all installations, the optimal value of b in the identical retailers and the related accuracy is assessed through simulation. 相似文献
929.
Majid Adib 《Numerical Linear Algebra with Applications》2008,15(7):637-642
In 1979, Gay proved that Broyden's methods, when used for n‐square linear systems, terminate in at most 2n iterations (SIAM J. Numer. Anal. 1979; 16 :623–630). Also, the ABS methods were introduced in 1984 (Numer. Math. 1984; 45 :1361–1376). In this paper we show another (handy) proof of Gay's theorem by these algorithms. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
930.
The possibility of material design technology to obtain negative refractive indices poses the question on the optical properties of aspherical surfaces made from such media. Here, the special aspherical surfaces connected with Cartesian ovaloides are discussed in the case of a negative refractive index. A subset of the Cartesian ovaloides contains spheres which allow aplanatic imaging in the well-known kind. A sign change of the refractive index shows changes in the virtual character of the aplanatic images. 相似文献