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52. Recent trends and future directions in vertex-transitive graphsKlavdija Kutnar, Dragan Marušič, 2008, original scientific article Abstract: A graph is said to be vertex-transitive if its automorphism group acts transitively on the vertex set. Some recent developments and possible future directions regarding two famous open problems, asking about existence of Hamilton paths and existence of semiregular automorphisms in vertex-transitive graphs, are discussed, together with some recent results on arc-transitive graphs and half-arc-transitive graphs, two special classes of vertex-transitive graphs that have received particular attention over the last decade.
Keywords: vertex-transitive graph, arc-transitive graph, half-arc-transitive graph, Hamilton cycle, Hamilton path, semiregular group, (im)primitive group
Published in RUP: 15.10.2013; Views: 3172; Downloads: 132
 Full text (183,49 KB) |
53. On 2-fold covers of graphsYan-Quan Feng, Klavdija Kutnar, Aleksander Malnič, Dragan Marušič, 2008, original scientific article Abstract: A regular covering projection ▫$\wp : \widetilde{X} \to X$▫ of connected graphs is ▫$G$▫-admissible if ▫$G$▫ lifts along ▫$\wp$▫. Denote by ▫$\tilde{G}$▫ the lifted group, and let CT▫$(\wp)$▫ be the group of covering transformations. The projection is called ▫$G$▫-split whenever the extension ▫{$\mathrm{CT}}(\wp) \to \tilde{G} \to G$▫ splits. In this paper, split 2-covers are considered, with a particular emphasis given to cubic symmetric graphs. Supposing that ▫$G$▫ is transitive on ▫$X$▫, a ▫$G$▫-split cover is said to be ▫$G$▫-split-transitive if all complements ▫$\tilde{G} \cong G$▫ of CT▫$(\wp)$▫ within ▫$\tilde{G}$▫ are transitive on ▫$\widetilde{X}$▫; it is said to be ▫$G$▫-split-sectional whenever for each complement ▫$\tilde{G}$▫ there exists a ▫$\tilde{G}$▫-invariant section of ▫$\wp$▫; and it is called ▫$G$▫-split-mixed otherwise. It is shown, when ▫$G$▫ is an arc-transitive group, split-sectional and split-mixed 2-covers lead to canonical double covers. Split-transitive covers, however, are considerably more difficult to analyze. For cubic symmetric graphs split 2-cover are necessarily canonical double covers (that is, no ▫$G$▫-split-transitive 2-covers exist) when ▫$G$▫ is 1-regular or 4-regular. In all other cases, that is, if ▫$G$▫ is ▫$s$▫-regular, ▫$s=2,3$▫ or ▫$5$▫, a necessary and sufficient condition for the existence of a transitive complement ▫$\tilde{G}$▫ is given, and moreover, an infinite family of split-transitive 2-covers based on the alternating groups of the form ▫$A_{12k+10}$▫ is constructed. Finally, chains of consecutive 2-covers, along which an arc-transitive group ▫$G$▫ has successive lifts, are also considered. It is proved that in such a chain, at most two projections can be split. Further, it is shown that, in the context of cubic symmetric graphs, if exactly two of them are split, then one is split-transitive and the other one is either split-sectional or split-mixed.
Keywords: graph theory, graphs, cubic graphs, symmetric graphs, ▫$s$▫-regular group, regular covering projection
Published in RUP: 15.10.2013; Views: 3670; Downloads: 34
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56. Saving and Empowering Young Lives in Europe (SEYLE)Danuta Wasserman, Vladimir Carli, Camilla Wasserman, Alan Apter, Judit Balazs, Renata Bracale, Romuald Brunner, Cendrine Bursztein-Lipsicas, Paul Corcoran, Doina Cosman, Tony Durkee, Dana Feldman, Julia Gadoros, Francis Guillemin, Christian Haring, Jean-Pierre Kahn, Michael Kaess, Helen Keeley, Dragan Marušič, Bogdan Nemes, Vita Poštuvan, Stella Reiter-Theil, Franz Resch, Franz Resch, Pilar Sáiz, Marco Sarchiapone, Merike Sisask, Airi Varnik, Christina W. Hoven, 2010, original scientific article Keywords: samomori, samomorilnost, preventiva, programi, Evropa
Published in RUP: 15.10.2013; Views: 8270; Downloads: 36
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59. The spanning laceability on the faulty bipartite hypercube-like networksCheng-Kuan Lin, Yuan-Hsiang Teng, Jimmy J. M. Tan, Lih-Hsing Hsu, Dragan Marušič, 2013, original scientific article Keywords: Hamiltonian, Hamiltonian laceable, Hypercube networks, Hypercube-like network, Spanning laceability
Published in RUP: 15.10.2013; Views: 2716; Downloads: 85
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60. The strongly distance-balanced property of the generalized Petersen graphsKlavdija Kutnar, Aleksander Malnič, Dragan Marušič, Štefko Miklavič, 2009, original scientific article Abstract: A graph ▫$X$▫ is said to be strongly distance-balanced whenever for any edge ▫$uv$▫ of ▫$X$▫ and any positive integer ▫$i$▫, the number of vertices at distance ▫$i$▫ from ▫$u$▫ and at distance ▫$i + 1$▫ from ▫$v$▫ is equal to the number of vertices at distance ▫$i + 1$▫ from ▫$u$▫ and at distance ▫$i$▫ from ▫$v$▫. It is proven that for any integers ▫$k \ge 2$▫ and ▫$n \ge k^2 + 4k + 1$▫, the generalized Petersen graph GP▫$(n, k)$▫ is not strongly distance-balanced.
Keywords: graph, strongy distance-balanced, generalized Petersen graph
Published in RUP: 15.10.2013; Views: 3109; Downloads: 132
Full text (146,23 KB) |
