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R.G. Gibson 《Discrete Mathematics》2008,308(24):5937-5943
For any permutation π of the vertex set of a graph G, the graph πG is obtained from two copies G′ and G″ of G by joining u∈V(G′) and v∈V(G″) if and only if v=π(u). Denote the domination number of G by γ(G). For all permutations π of V(G), γ(G)≤γ(πG)≤2γ(G). If γ(πG)=γ(G) for all π, then G is called a universal fixer. We prove that graphs without 5-cycles are not universal fixers, from which it follows that bipartite graphs are not universal fixers. 相似文献
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For any permutation π of the vertex set of a graph G, the generalized prism πG is obtained by joining two copies of G by the matching {uπ(u):u∈V(G)}. Denote the domination number of G by γ(G). If γ(πG)=γ(G) for all π, then G is called a universal fixer. The edgeless graphs are the only known universal fixers, and are conjectured to be the only universal fixers. We prove that claw-free graphs are not universal fixers. 相似文献
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Geometrical optics analysis for reduction of trapezoidal image distortion in a single prism-based optical fingerprint scanner 总被引:2,自引:0,他引:2
Sarun Sumriddetchkajorn Suwannee Phoojaruenchanachai 《Optics and Lasers in Engineering》2007,45(1):229-239
A single prism-based optical fingerprint scanner structure is mathematically analyzed by using geometrical optics approach. Important parameters including a tilting angle of the fingerprint accepting plane, a geometrical-optic distant difference, a trapezoidal image distortion, an object compression ratio, and an orientation of a two-dimensional image sensor are formulated for the first time in terms of all three angles of the prism and the prism material. In addition, based on our mathematical model, we propose to design all three angles of the prism in such a way that the plane accepting the fingertip observed from one side of the prism is normal to the optical axis of the system. In this way, the imaging plane is perpendicular to the optical axis, eliminating the trapezoidal image distortion and leading to ease of implementation. Experimental verification using three commercially available dispersion prisms made from three different glass materials and one prism based on our design concept shows that a prism with higher refractive index provides lower trapezoidal image distortion. The experimental data generally obeys our theoretical analysis. 相似文献
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