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AIMS To investigate the prevalence of pathological internet use (PIU) and maladaptive internet use (MIU) among adolescents in 11 European countries in relation to demographic, social factors and internet accessibility. DESIGN Cross-sectional survey. SETTING The 7th Framework European Union (EU) funded project, Saving and Empowering Young Lives in Europe… (More)
The following problem is considered: if H is a semiregular abelian subgroup of a transitive permutation group G acting on a finite set X, find conditions for (non)existence of G-invariant partitions of X and give their description in terms of orbits of H. Conditions and descriptions presented in this paper are derived by studying spectral properties of the… (More)
In this paper we study finite, connected, 4-valent graphs X which admit an action of a group G which is transitive on vertices and edges, but not transitive on the arcs of X. Such a graph X is said to be (G, 1Â2)-transitive. The group G induces an orientation of the edges of X, and a certain class of cycles of X (called alternating cycles) determined by the… (More)
Certain graph-theoretic properties and alternative deenitions of the Gray graph, the smallest known cubic edge-but not vertex-transitive graph, are discussed in detail.