Describing Neighborhoods of 5-Vertices in a Class of 3-Polytopes with Minimum Degree 5

Lebesgue proved in 1940 that each 3-polytope with minimum degree 5 contains a 5-vertex for which the set of degrees of its neighbors is majorized by one of the following sequences(6, 6, 7, 7, 7), (6, 6, 6, 7, 9), (6, 6, 6, 6, 11)(5, 6, 7, 7, 8), (5, 6, 6, 7, 12), (5, 6, 6, 8, 10), (5, 6, 6, 6, 17)(5, 5, 7, 7, 13), (5, 5, 7, 8, 10), (5, 5, 6, 7, 27), (5, 5, 6, 6,∞), (5, 5, 6, 8, 15), (5, 5, 6, 9, 11)(5, 5, 5, 7, 41), (5, 5, 5, 8, 23), (5, 5, 5, 9, 17), (5, 5, 5, 10, 14), (5, 5, 5, 11, 13).We prove that each 3-polytope with minimum degree 5 without vertices of degree from 7 to 10 contains a 5-vertex whose set of degrees of its neighbors is majorized by one of the following sequences: (5, 6, 6, 5, ∞), (5, 6, 6, 6, 15), and (6, 6, 6, 6, 6), where all parameters are tight.     

A note on similarity solutions for boundary layer flows with prescribed heat flux

We study the third‐order nonlinear equation: f′′′ + (m + 2)ff′′ ? (2m + 1)f′² = 0 on (0, ∞), subject to the boundary conditions f(0) = ? γ ∈ ?, f′(∞) = 0 and f′′(0) = ?1. The problem arises in the study of similarity solutions for boundary layer flows with prescribed heat flux. We will address the following two open questions which were proposed by Brighi and Hoernel (Math. Methods Appl. Sci. 2005; 28 : 479–503): The first one is the uniqueness of bounded solutions for and γ>0, and the second one is the structure of solutions for and γ?0. Copyright © 2007 John Wiley & Sons, Ltd.     

Monochromatic paths in random tournaments

We prove that, with high probability, any 2‐edge‐coloring of a random tournament on n vertices contains a monochromatic path of length . This resolves a conjecture of Ben‐Eliezer, Krivelevich, and Sudakov and implies a nearly tight upper bound on the oriented size Ramsey number of a directed path.     

Structure theorem for tournaments omitting N5

A finite tournament T is tight if the class of finite tournaments omitting T is well‐quasi‐ordered. We show here that a certain tournament N₅ on five vertices is tight. This is one of the main steps in an exact classification of the tight tournaments, as explained in [10]; the third and final step is carried out in [11]. The proof involves an encoding of the indecomposable tournaments omitting N₅ by a finite alphabet, followed by an application of Kruskal's Tree Theorem. This problem arises in model theory and in computational complexity in a more general form, which remains open: the problem is to give an effective criterion for a finite set {T₁,…,T_k} of finite tournaments to be tight in the sense that the class of all finite tournaments omitting each of T₁,…,T_k is well‐quasi‐ordered. © 2003 Wiley Periodicals, Inc. J Graph Theory 42: 165–192, 2003     

若干圈限制平面图的星边染色

图G的星边染色是指G的一个正常边染色,使得G中任一长为4的路和长为4的圈均不是2-边染色的.图G的星边色数χ’st(G)表示图G有星边染色的最小颜色数.设G是最大度为Δ的平面图,我们证明了:(1)若G不含4-圈,则χ’st(G)≤[1.5Δ]+15;(2)若g≥5,则χ’st(G)≤[1.5Δ」+10;(3)若g=7,则χ’st(G)≤[1.5Δ」+6.     

Graphs with No Induced Five‐Vertex Path or Antipath

We prove that a graph G contains no induced ‐vertex path and no induced complement of a ‐vertex path if and only if G is obtained from 5‐cycles and split graphs by repeatedly applying the following operations: substitution, split unification, and split unification in the complement, where split unification is a new class‐preserving operation introduced here.     

Star coloring planar graphs from small lists

A star coloring of a graph is a proper vertex‐coloring such that no path on four vertices is 2‐colored. We prove that the vertices of every planar graph of girth 6 (respectively 7, 8) can be star colored from lists of size 8 (respectively 7, 6). We give an example of a planar graph of girth 5 that requires 6 colors to star color. © 2009 Wiley Periodicals, Inc. J Graph Theory 63: 324–337, 2010     

Facial Nonrepetitive Vertex Coloring of Plane Graphs

A sequence is a repetition. A sequence S is nonrepetitive, if no subsequence of consecutive terms of S is a repetition. Let G be a plane graph. That is, a planar graph with a fixed embedding in the plane. A facial path consists of consecutive vertices on the boundary of a face. A facial nonrepetitive vertex coloring of a plane graph G is a vertex coloring such that the colors assigned to the vertices of any facial path form a nonrepetitive sequence. Let denote the minimum number of colors of a facial nonrepetitive vertex coloring of G. Harant and Jendrol’ conjectured that can be bounded from above by a constant. We prove that for any plane graph G.     

Splitting Planar Graphs of Girth 6 into Two Linear Forests with Short Paths

Recently, Borodin, Kostochka, and Yancey (Discrete Math 313(22) (2013), 2638–2649) showed that the vertices of each planar graph of girth at least 7 can be 2‐colored so that each color class induces a subgraph of a matching. We prove that any planar graph of girth at least 6 admits a vertex coloring in colors such that each monochromatic component is a path of length at most 14. Moreover, we show a list version of this result. On the other hand, for each positive integer , we construct a planar graph of girth 4 such that in any coloring of vertices in colors there is a monochromatic path of length at least t. It remains open whether each planar graph of girth 5 admits a 2‐coloring with no long monochromatic paths.     

A Hybrid Finite Volume Method for Advection Equations and Its Applications in Population Dynamics

We present in this article a very adapted finite volume numerical scheme for transport type‐equation. The scheme is an hybrid one combining an anti‐dissipative method with down‐winding approach for the flux (Després and Lagoutière, C R Acad Sci Paris Sér I Math 328(10) (1999), 939–944; Goudon, Lagoutière, and Tine, Math Method Appl Sci 23(7) (2013), 1177–1215) and an high accurate method as the WENO5 one (Jiang and Shu, J Comput Phys 126 (1996), 202–228). The main goal is to construct a scheme able to capture in exact way the numerical solution of transport type‐equation without artifact like numerical diffusion or without “stairs” like oscillations and this for any regular or discontinuous initial distribution. This kind of numerical hybrid scheme is very suitable when properties on the long term asymptotic behavior of the solution are of central importance in the modeling what is often the case in context of population dynamics where the final distribution of the considered population and its mass preservation relation are required for prediction. © 2017 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 33: 1114–1142, 2017     

The size of minimum 3‐trees

A 3‐uniform hypergraph (3‐graph) is said to be tight, if for any 3‐partition of its vertex set there is a transversal triple. We give the final steps in the proof of the conjecture that the minimum number of triples in a tight 3‐graph on n vertices is exactly . © 2006 Wiley Periodicals, Inc. J Graph Theory 54: 103–114, 2007     

Decomposing the real line into Borel sets closed under addition

We consider decompositions of the real line into pairwise disjoint Borel pieces so that each piece is closed under addition. How many pieces can there be? We prove among others that the number of pieces is either at most 3 or uncountable, and we show that it is undecidable in and even in the theory if the number of pieces can be uncountable but less than the continuum. We also investigate various versions: what happens if we drop the Borelness requirement, if we replace addition by multiplication, if the pieces are subgroups, if we partition (0, ∞), and so on.     

The width of quadrangulations of the projective plane

We show that every 4‐chromatic graph on n vertices, with no two vertex‐disjoint odd cycles, has an odd cycle of length at most . Let G be a nonbipartite quadrangulation of the projective plane on n vertices. Our result immediately implies that G has edge‐width at most , which is sharp for infinitely many values of n. We also show that G has face‐width (equivalently, contains an odd cycle transversal of cardinality) at most , which is a constant away from the optimal; we prove a lower bound of . Finally, we show that G has an odd cycle transversal of size at most inducing a single edge, where Δ is the maximum degree. This last result partially answers a question of Nakamoto and Ozeki.     

Balanced caterpillars of maximum degree 3 and with hairs of arbitrary length are subgraphs of their optimal hypercube

A caterpillar is a tree having a path that contains all vertices of of degree at least 3. We show in this article that every balanced caterpillar with maximum degree 3 and 2ⁿ vertices is a subgraph of the n‐dimensional hypercube. This solves a long‐standing open problem and generalizes a result of Havel and Liebl (1986), who considered only such caterpillars that have a path containing all vertices of degree at least 2.     

Covering 2‐connected 3‐regular graphs with disjoint paths

A path cover of a graph is a set of disjoint paths so that every vertex in the graph is contained in one of the paths. The path cover number of graph G is the cardinality of a path cover with the minimum number of paths. Reed in 1996 conjectured that a 2‐connected 3‐regular graph has path cover number at most . In this article, we confirm this conjecture.