共查询到20条相似文献,搜索用时 15 毫秒
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In this paper, we discuss new upper bounds for the chromatic numbers of and with intervals of forbidden distances. 相似文献
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We study some properties of -homotopy groups: geometric interpretations of connectivity, excision results, and a re-interpretation of quotients by free actions of connected solvable groups in terms of covering spaces in the sense of -homotopy theory. These concepts and results are well suited to the study of certain quotients via geometric invariant theory. As a case study in the geometry of solvable group quotients, we investigate -homotopy groups of smooth toric varieties. We give simple combinatorial conditions (in terms of fans) guaranteeing vanishing of low degree -homotopy groups of smooth (proper) toric varieties. Finally, in certain cases, we can actually compute the “next” non-vanishing -homotopy group (beyond ) of a smooth toric variety. From this point of view, -homotopy theory, even with its exquisite sensitivity to algebro-geometric structure, is almost “as tractable” (in low degrees) as ordinary homotopy for large classes of interesting varieties. 相似文献
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We study the dynamics of infinitely many Cucker–Smale (C–S) flocking particles under the interplay of random communication and incompressible fluids. For the dynamics of an ensemble of flocking particles, we use the kinetic Cucker–Smale–Fokker–Planck (CS–FP) equation with a degenerate diffusion, whereas for the fluid component, we use the incompressible Navier–Stokes (N–S) equations. These two subsystems are coupled via the drag force. For this coupled model, we present the global existence of weak and strong solutions in . Under the extra regularity assumptions of the initial data, the unique solvability of strong solutions is also established in . In a large coupling regime and periodic spatial domain , we show that the velocities of C–S particles and fluids are asymptotically aligned to two constant velocities which may be different. 相似文献
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We study the Keller–Segel system in when the chemoattractant concentration is described by a parabolic equation. We prove that the critical space, with some similarity to the elliptic case, is that the initial bacteria density satisfies , , and that the chemoattractant concentration satisfies . In these spaces, we prove that small initial data give rise to global solutions that vanish as the heat equation for large times and that exhibit a regularizing effect of hypercontractivity type. To cite this article: L. Corrias, B. Perthame, C. R. Acad. Sci. Paris, Ser. I 342 (2006). 相似文献
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Masoud Hassani 《Comptes Rendus Mathematique》2017,355(11):1133-1137
In this paper, we study the irreducible representation of in . This action preserves a quadratic form with signature . Thus, it acts conformally on the 3-dimensional Einstein universe . We describe the orbits induced in and its complement in . This work completes the study in [2], and is one element of the classification of cohomogeneity one actions on [5]. 相似文献
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Xiaopeng Zhao 《Comptes Rendus Mathematique》2017,355(3):310-317
This paper discusses the large-time behavior of solutions for a new Hall–MHD system in . Using the Fourier splitting method, we establish the upper bound of the time-decay rate in for weak solutions. 相似文献
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Cleopatra Christoforou 《Journal of Differential Equations》2012,252(3):2845-2863
The isometric immersion problem for surfaces embedded into is studied via the fluid dynamic framework introduced in Chen et al. (2010) [6] as a system of balance laws of mixed-type. The techniques developed in the theory of weak solutions of bounded variation in continuum physics are employed to deal with the isometric immersions in the setting of differential geometry. The so-called BV framework is formed that establishes convergence of approximate solutions of bounded variation to the Gauss–Codazzi system and yields the isometric realization of two-dimensional surfaces into . Local and global existence results are established for weak solutions of small bounded variation to the Gauss–Codazzi system for negatively curved surfaces that admit equilibrium configurations. As an application, the case of catenoidal shell of revolution is provided. 相似文献
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It is known that the category of homogeneous bundles on is equivalent to the category of representations of a quiver with relation. In this paper we make use of this equivalence to describe a family of G-exceptional bundles on and to prove that they are stable. We also study the G-exceptionality of Fibonacci bundles on . 相似文献
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