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On edge detour graphs

100%

Santhakumaran A. P. , Athisayanathan S.

Discussiones Mathematicae Graph Theory

2010

tom 30

nr 1

155-174

For two vertices u and v in a graph G = (V,E), the detour distance D(u,v) is the length of a longest u-v path in G. A u-v path of length D(u,v) is called a u-v detour. A set S ⊆V is called an edge detour set if every edge in G lies on a detour joining a pair of vertices of S. The edge detour number dn₁(G) of G is the minimum order of its edge detour sets and any edge detour set of order dn₁(G) is an edge detour basis of G. A connected graph G is called an edge detour graph if it has an edge detour set. It is proved that for any non-trivial tree T of order p and detour diameter D, dn₁(T) ≤ p-D+1 and dn₁(T) = p-D+1 if and only if T is a caterpillar. We show that for each triple D, k, p of integers with 3 ≤ k ≤ p-D+1 and D ≥ 4, there is an edge detour graph G of order p with detour diameter D and dn₁(G) = k. We also show that for any three positive integers R, D, k with k ≥ 3 and R < D ≤ 2R, there is an edge detour graph G with detour radius R, detour diameter D and dn₁(G) = k. Edge detour graphs G with detour diameter D ≤ 4 are characterized when dn₁(G) = p-2 or dn₁(G) = p-1.

The vertex detour hull number of a graph

88%

Santhakumaran A. , Ullas Chandran S.

Discussiones Mathematicae Graph Theory

2012

tom 32

nr 2

321-330

For vertices x and y in a connected graph G, the detour distance D(x,y) is the length of a longest x - y path in G. An x - y path of length D(x,y) is an x - y detour. The closed detour interval I_D[x,y] consists of x,y, and all vertices lying on some x -y detour of G; while for S ⊆ V(G), $I_D[S] = ⋃_{x,y ∈ S} I_D[x,y]$. A set S of vertices is a detour convex set if $I_D[S] = S$. The detour convex hull $[S]_D$ is the smallest detour convex set containing S. The detour hull number dh(G) is the minimum cardinality among subsets S of V(G) with $[S]_D = V(G)$. Let x be any vertex in a connected graph G. For a vertex y in G, denoted by $I_D[y]^x$, the set of all vertices distinct from x that lie on some x - y detour of G; while for S ⊆ V(G), $I_D[S]^x = ⋃_{y ∈ S} I_D[y]^x$. For x ∉ S, S is an x-detour convex set if $I_D[S]^x = S$. The x-detour convex hull of S, $[S]^x_D$ is the smallest x-detour convex set containing S. A set S is an x-detour hull set if $[S]^x_D = V(G) -{x}$ and the minimum cardinality of x-detour hull sets is the x-detour hull number dhₓ(G) of G. For x ∉ S, S is an x-detour set of G if $I_D[S]^x = V(G) - {x}$ and the minimum cardinality of x-detour sets is the x-detour number dₓ(G) of G. Certain general properties of the x-detour hull number of a graph are studied. It is shown that for each pair of positive integers a,b with 2 ≤ a ≤ b+1, there exist a connected graph G and a vertex x such that dh(G) = a and dhₓ(G) = b. It is proved that every two integers a and b with 1 ≤ a ≤ b, are realizable as the x-detour hull number and the x-detour number respectively. Also, it is shown that for integers a,b and n with 1 ≤ a ≤ n -b and b ≥ 3, there exist a connected graph G of order n and a vertex x such that dhₓ(G) = a and the detour eccentricity of x, $e_D(x) = b$. We determine bounds for dhₓ(G) and characterize graphs G which realize these bounds.

Detour chromatic numbers

75%

Frick M. , Bullock F.

Discussiones Mathematicae Graph Theory

2001

tom 21

nr 2

283-291

The nth detour chromatic number, χₙ(G) of a graph G is the minimum number of colours required to colour the vertices of G such that no path with more than n vertices is monocoloured. The number of vertices in a longest path of G is denoted by τ( G). We conjecture that χₙ(G) ≤ ⎡(τ(G))/n⎤ for every graph G and every n ≥ 1 and we prove results that support the conjecture. We also present some sufficient conditions for a graph to have nth chromatic number at most 2.

Budowa i utrzymanie mostów składanych na przeprawach tymczasowych

63%

Szelka J. , Wysoczański A.

Mosty

2023

tom nr 2

36-39

W artykule przedstawiono przykłady zastosowań konstrukcji składanych do budowy mostów objazdowych we Wrocławiu. Zaprezentowane konstrukcje mostów składanych (DMS-65, MS-54, MS 22-80, KD-66C) pozwalają na łatwy i szybki montaż przęseł i podpór w różnych układach konstrukcyjnych. W końcowej części opracowania podano perspektywy rozwoju tych konstrukcji.

The article presents examples of the use of folding structures for the construction of bypass bridges in Wrocław. The presented structures of folding bridges (DMS-65, MS-54, MS 22-80, KD-66C) allow for easy and quick assembly of spans and supports in various structural systems. In the final part of the paper, the prospects for the development of these structures are given.