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991.
992.
993.
In this paper, we give a classification of (finite or countable) ?0‐categorical coloured linear orders, generalizing Rosenstein's characterization of ?0‐categorical linear orderings. We show that they can all be built from coloured singletons by concatenation and ?n‐combinations (for n ≥ 1). We give a method using coding trees to describe all structures in our list (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
994.
It is an interesting topic to determine the structure of a finite group with a given number of elements of maximal order. In this article, we classify finite groups with 24 elements of maximal order. 相似文献
995.
Clestin Wafo Soh 《Communications in Nonlinear Science & Numerical Simulation》2010,15(2):139-143
We show that the structure of the Lie symmetry algebra of a system of n linear second-order ordinary differential equations with constant coefficients depends on at most n-1 parameters. The tools used are Jordan canonical forms and appropriate scaling transformations. We put our approach to test by presenting a simple proof of the fact that the dimension of the symmetry Lie algebra of a system of two linear second-order ordinary differential with constant coefficients is either 7, 8 or 15. Also, we establish for the first time that the dimension of the symmetry Lie algebra of a system of three linear second-order ordinary differential equations with constant coefficients is 10, 12, 13 or 24. 相似文献
996.
利用推广的邻格方法,完成了Q(61/2)上秩4的在一个阿基米德除子上正定,在另一阿基米德除子上负定的所有幺模格种的分类. 相似文献
997.
Let S be a blocking set in an inversive plane of order q. It was shown by Bruen and Rothschild 1 that |S| ≥ 2q for q ≥ 9. We prove that if q is sufficiently large, C is a fixed natural number and |S = 2q + C, then roughly 2/3 of the circles of the plane meet S in one point and 1/3 of the circles of the plane meet S in four points. The complete classification of minimal blocking sets in inversive planes of order q ≤ 5 and the sizes of some examples of minimal blocking sets in planes of order q ≤ 37 are given. Geometric properties of some of these blocking sets are also studied. © 2004 Wiley Periodicals, Inc. 相似文献
998.
Min Chih Lin Veronica A. Moyano Dieter Rautenbach Jayme L. Szwarcfiter 《Journal of Graph Theory》2015,78(4):258-268
A matching M of a graph G is a dominating induced matching (DIM) of G if every edge of G is either in M or adjacent with exactly one edge in M. We prove sharp upper bounds on the number of DIMs of a graph G and characterize all extremal graphs. Our results imply that if G is a graph of order n, then ; provided G is triangle‐free; and provided and G is connected. 相似文献
999.
In this article, we continue the study of 2‐colorings in hypergraphs. A hypergraph is 2‐colorable if there is a 2‐coloring of the vertices with no monochromatic hyperedge. Let denote the class of all k‐uniform k‐regular hypergraphs. It is known (see Alon and Bregman [Graphs Combin. 4 (1988) 303–306] and Thomassen [J. Amer. Math. Soc. 5 (1992), 217–229] that every hypergraph is 2‐colorable, provided . As remarked by Alon and Bregman the result is not true when , as may be seen by considering the Fano plane. Indeed there are several constructions for building infinite families of hypergraphs in that are not 2‐colorable. Our main result in this paper is a strengthening of the above results. For this purpose, we define a set X of vertices in a hypergraph H to be a free set in H if we can 2‐color such that every edge in H receives at least one vertex of each color. We conjecture that for , every hypergraph has a free set of size in H. We show that the bound cannot be improved for any and we prove our conjecture when . Our proofs use results from areas such as transversal in hypergraphs, cycles in digraphs, and probabilistic arguments. 相似文献
1000.
R. Julian R. Abel 《组合设计杂志》2015,23(4):135-139
In this article, we provide direct constructions for five mutually orthogonal Latin squares (MOLS) of orders and 60. For , these come from a new (60, 6, 1) difference matrix. For , the required construction is obtained by combining two different methods that were used in the constructions of four MOLS(14) and eight MOLS(36). 相似文献