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本文从建立椭园衍射模型入手,探讨了球形颗粒与真实颗粒在傅立叶谱上的数量关系,提出了一种傅立叶粒径定义,该定义为激光衍射法测非球形颗粒,提供了一种可行的方法。 相似文献
204.
栓皮栎,杉木和火炬松根际与非根际土壤氮素及pH差异的研究 总被引:11,自引:0,他引:11
厉婉华 《南京林业大学学报(自然科学版)》1996,20(2):49-52
初步研究了南京林业大学下蜀林场栓皮栎,杉木和火炬松根际与非根际土壤氮素状况及土壤pH的差异,结果表明三个树种根际土壤全氮含量都明显高于非根际土壤,无机氮的季节变化是栓皮栎根际无机氮含量皆高于非根际土壤,杉木和火炬松根际土壤无机氮含量积累或亏缺或与非根际土壤接近。三个树种对土壤pH的影响是:栓皮栎根际土壤pH大于非根际土壤pH,杉木和火炬松则是根际土壤pH小于非根际土壤pH。 相似文献
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C. Balbuena 《Discrete Mathematics》2007,307(6):659-667
The restricted connectivity κ′(G) of a connected graph G is defined as the minimum cardinality of a vertex-cut over all vertex-cuts X such that no vertex u has all its neighbors in X; the superconnectivity κ1(G) is defined similarly, this time considering only vertices u in G-X, hence κ1(G)?κ′(G). The minimum edge-degree of G is ξ(G)=min{d(u)+d(v)-2:uv∈E(G)}, d(u) standing for the degree of a vertex u. In this paper, several sufficient conditions yielding κ1(G)?ξ(G) are given, improving a previous related result by Fiol et al. [Short paths and connectivity in graphs and digraphs, Ars Combin. 29B (1990) 17-31] and guaranteeing κ1(G)=κ′(G)=ξ(G) under some additional constraints. 相似文献
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The curvature of a polytope, defined as the largest possible total curvature of the associated central path, can be regarded
as a continuous analogue of its diameter. We prove an analogue of the result of Klee and Walkup. Namely, we show that if the
order of the curvature is less than the dimension d for all polytopes defined by 2d inequalities and for all d, then the order of the curvature is less that the number of inequalities for all polytopes. 相似文献
209.
The degree/diameter problem is to determine the largest graphs or digraphs of given maximum degree and given diameter. This paper deals with directed graphs. General upper bounds, called Moore bounds, exist for the largest possible order of such digraphs of maximum degree d and given diameter k. It is known that simulated annealing and genetic algorithm are effective techniques to identify global optimal solutions.This paper describes our attempt to build a Hybrid Simulated Annealing and Genetic Algorithm (HSAGA) that can be used to construct large digraphs. We present our new results obtained by HSAGA, as well as several related open problems. 相似文献
210.
Martin Lätsch 《Discrete Applied Mathematics》2008,156(17):3194-3202
As a generalization of directed and undirected graphs, Edmonds and Johnson [J. Edmonds, E.L. Johnson, Matching: A well-solved class of linear programs, in: R. Guy, H. Hanani, N. Sauer, J. Schönheim (Eds.), Combinatorial Structures and their Applications, Gordon and Breach, New York, 1970, pp. 88-92] introduced bidirected graphs. A bidirected graph is a graph each arc of which has either two positive end-vertices (tails), two negative end-vertices (heads), or one positive end-vertex (tail) and one negative end-vertex (head). We extend the notion of directed paths, distance, diameter and strong connectivity from directed to bidirected graphs and characterize those undirected graphs that allow a strongly connected bidirection. Considering the problem of finding the minimum diameter of all strongly connected bidirections of a given undirected graph, we generalize a result of Fomin et al. [F.V. Fomin, M. Matamala, E. Prisner, I. Rapaport, Bilateral orientations in graphs: Domination and AT-free classes, in: Proceedings of the Brazilian Symposium on Graphs, Algorithms and Combinatorics, GRACO 2001, in: Electronics Notes in Discrete Mathematics, vol. 7, Elsevier Science Publishers, 2001] about directed graphs and obtain an upper bound for the minimum diameter which depends on the minimum size of a dominating set and the number of bridges in the undirected graph. 相似文献