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991.
M. D. Guay 《Acta Mathematica Hungarica》2004,105(3):241-248
Axioms are given for a preconvexity space and certain consequences obtained. In particular, it is shown that in a very natural
way, a preconvexity on a space yields an abstract convexity space in much the same manner as a proximity yields a topological
space.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
992.
In this note we make a correction in the paper [1] by two of the authors. Specifically we modify an auxiliary localization
result and prove that the applications to the saturation theory of some outstanding conservative operators remain valid. Moreover,
we enrich a corollary dealing with the well-known Szász-Mirakjan operators.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
993.
Discrete global descent method for discrete global optimization and nonlinear integer programming 总被引:2,自引:0,他引:2
A novel method, entitled the discrete global descent method, is developed in this paper to solve discrete global optimization
problems and nonlinear integer programming problems. This method moves from one discrete minimizer of the objective function
f to another better one at each iteration with the help of an auxiliary function, entitled the discrete global descent function.
The discrete global descent function guarantees that its discrete minimizers coincide with the better discrete minimizers
of f under some standard assumptions. This property also ensures that a better discrete minimizer of f can be found by some classical local search methods. Numerical experiments on several test problems with up to 100 integer
variables and up to 1.38 × 10104 feasible points have demonstrated the applicability and efficiency of the proposed method. 相似文献
994.
Motivated by the central limit problem for convex bodies, we study normal approximation of linear functionals of high-dimensional
random vectors with various types of symmetries. In particular, we obtain results for distributions which are coordinatewise
symmetric, uniform in a regular simplex, or spherically symmetric. Our proofs are based on Stein’s method of exchangeable
pairs; as far as we know, this approach has not previously been used in convex geometry. The spherically symmetric case is
treated by a variation of Stein’s method which is adapted for continuous symmetries.
This work was done while at Stanford University. 相似文献
995.
Tom Edgar 《Journal of Algebraic Combinatorics》2007,26(3):357-362
Twisted Bruhat orders are certain partial orders on a Coxeter system (W,S) associated to initial sections of reflection orders, which are certain subsets of the set of reflections T of a Coxeter system. We determine which subsets of T give rise to a partial order on W in the same way. 相似文献
996.
Leo Brewin 《General Relativity and Gravitation》2007,39(4):521-528
We show by an almost elementary calculation that the ADM mass of an asymptotically flat space can be computed as a limit involving
a rate of change of area of a closed 2-surface. The result is essentially the same as that given by David Brown and York (Phys.
Rev. D 55, 1977–1984 1997; Phys. Rev. D 47, 1407–1419 1993). We will prove this result in two ways, first by direct calculation from the original formula as given by
Arnowitt, Deser and Misner and second as a corollary of an earlier result by Brewin for the case of simplicial spaces. 相似文献
997.
Alexander G. Ramm Alexandra B. Smirnova Angelo Favini 《Annali di Matematica Pura ed Applicata》2003,182(1):37-52
A nonlinear operator equation F(x)=0, F:H→H, in a Hilbert space is considered. Continuous Newton’s-type procedures based on a construction of a dynamical system with
the trajectory starting at some initial point x
0 and becoming asymptotically close to a solution of F(x)=0 as t→+∞ are discussed. Well-posed and ill-posed problems are investigated.
Received: June 29, 2001; in final form: February 26, 2002?Published online: February 20, 2003
This paper was finished when AGR was visiting Institute for Theoretical Physics, University of Giessen. The author thanks
DAAD for support 相似文献
998.
C. D. Habben 《无机化学与普通化学杂志》1991,606(1):229-232
Synthesis of Boron-Sulfur(IV)-Nitrogen Heterocycles The reaction of bis(lithio.tert.-butylamino)phenylborane with tert.-butyldichlorosulfimide and bischlorodimethylsilylsulfodiimide respectively leads to four- or eight-membered heterocycles. The disulfanebridge of one dithiazadiborolidine can be replaced by the ? N?S?N-sequence to yield a Thiatriazadiborine. 1H, 11B, 13C-NMR, mass spectra, and analytical data are reported and discussed. 相似文献
999.
Sans résumé
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1000.
Joseph Majdalani Sjoerd W. Rienstra 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》2007,58(2):289-308
The bidirectional vortex refers to the bipolar, coaxial swirling motion that can be triggered, for example, in cyclone separators
and some liquid rocket engines with tangential aft-end injectors. In this study, we present an exact solution to describe
the corresponding bulk motion in spherical coordinates. To do so, we examine both linear and nonlinear solutions of the momentum
and vorticity transport equations in spherical coordinates. The assumption will be that of steady, incompressible, inviscid,
rotational, and axisymmetric flow. We further relate the vorticity to some power of the stream function. At the outset, three
possible types of similarity solutions are shown to fulfill the momentum equation. While the first type is incapable of satisfying
the conditions for the bidirectional vortex, it can be used to accommodate other physical settings such as Hill’s vortex.
This case is illustrated in the context of inviscid flow over a sphere. The second leads to a closed-form analytical expression
that satisfies the boundary conditions for the bidirectional vortex in a straight cylinder. The third type is more general
and provides multiple solutions. The spherical bidirectional vortex is derived using separation of variables and the method
of variation of parameters. The three-pronged analysis presented here increases our repertoire of general mean flow solutions
that rarely appear in spherical geometry. It is hoped that these special forms will permit extending the current approach
to other complex fluid motions that are easier to capture using spherical coordinates. 相似文献