共查询到20条相似文献,搜索用时 951 毫秒
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《Journal of Pure and Applied Algebra》2022,226(10):107074
For a commutative ring A we consider a related graph, , whose vertices are the unimodular rows of length 2 up to multiplication by units. We prove that is path-connected if and only if A is a -ring, in the terminology of P. M. Cohn. Furthermore, if denotes the clique complex of , we prove that is simply connected if and only if A is universal for . More precisely, our main theorem is that for any commutative ring A the fundamental group of is isomorphic to the group modulo the subgroup generated by symbols. 相似文献
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《Discrete Mathematics》2022,345(8):112917
Let and denote the flow number and the circular flow number of a flow-admissible signed graph , respectively. It is known that for every unsigned graph G. Based on this fact, in 2011 Raspaud and Zhu conjectured that holds also for every flow-admissible signed graph . This conjecture was disproved by Schubert and Steffen using graphs with bridges and vertices of large degree. In this paper we focus on cubic graphs, since they play a crucial role in many open problems in graph theory. For cubic graphs we show that if and only if and if , then . We also prove that all pairs of flow number and circular flow number that fulfil these conditions can be achieved in the family of bridgeless cubic graphs and thereby disprove the conjecture of Raspaud and Zhu even for bridgeless signed cubic graphs. Finally, we prove that all currently known flow-admissible graphs without nowhere-zero 5-flow have flow number and circular flow number 6 and propose several conjectures in this area. 相似文献
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We study the non-linear minimization problem on with , and : where presents a global minimum α at with . In order to describe the concentration of around , one needs to calibrate the behavior of with respect to s. The model case is In a previous paper dedicated to the same problem with , we showed that minimizers exist only in the range , which corresponds to a dominant non-linear term. On the contrary, the linear influence for prevented their existence. The goal of this present paper is to show that for , and , minimizers do exist. 相似文献
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《Discrete Mathematics》2022,345(8):112902
For a simple graph G, denote by n, , and its order, maximum degree, and chromatic index, respectively. A graph G is edge-chromatic critical if and for every proper subgraph H of G. Let G be an n-vertex connected regular class 1 graph, and let be obtained from G by splitting one vertex of G into two vertices. Hilton and Zhao in 1997 conjectured that must be edge-chromatic critical if , and they verified this when . In this paper, we prove it for . 相似文献
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Judit Abardia-Evéquoz Károly J. Böröczky Mátyás Domokos Dávid Kertész 《Journal of Functional Analysis》2019,276(11):3325-3362
The space of continuous, -equivariant, , and translation covariant valuations taking values in the space of real symmetric tensors on of rank is completely described. The classification involves the moment tensor valuation for and is analogous to the known classification of the corresponding tensor valuations that are -equivariant, although the method of proof cannot be adapted. 相似文献
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The paper investigates longtime dynamics of the Kirchhoff wave equation with strong damping and critical nonlinearities: , with . The well-posedness and the existence of global and exponential attractors are established, and the stability of the attractors on the perturbation parameter ? is proved for the IBVP of the equation provided that both nonlinearities and are of critical growth. 相似文献
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《Discrete Mathematics》2022,345(2):112663
Given graphs F and H, the generalized rainbow Turán number is the maximum number of copies of F in an n-vertex graph with a proper edge-coloring that contains no rainbow copy of H. B. Janzer determined the order of magnitude of for all and , and a recent result of O. Janzer implied that . We prove the corresponding upper bound for the remaining cases, showing that . This matches the known lower bound for k even and is conjectured to be tight for k odd. 相似文献
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