In this note,we show a sharp lower bound of min{Σ_(i=1)^(k)dG(u_(i)):u1u2...uk is a path of(2-)connected G}on its order such that(k-1)-iterated line graphs L^(k-1)(G)are hamiltonian.
Abstract A graph g is k-ordered Hamiltonian, 2 h k h n, if for every ordered sequence S of k distinct vertices of G, there exists a Hamiltonian cycle that encounters S in the given order. In this article, we prove tha...Abstract A graph g is k-ordered Hamiltonian, 2 h k h n, if for every ordered sequence S of k distinct vertices of G, there exists a Hamiltonian cycle that encounters S in the given order. In this article, we prove that if G is a graph on n vertices with degree sum of nonadjacent vertices at least $n+{{3k - 9} \over 2}$, then G is k-ordered Hamiltonian for k=3,4,...,￠${n \over {19}}$?. We also show that the degree sum bound can be reduced to n+ 2 ￠ ${k \over {2}}$ m 2 if $\kappa(G)\ge {{3k - 1} \over 2}$ or '(G) S 5k m 4. Several known results are generalized.展开更多
A graph G satisfies the Ore-condition if d（x）＋d（y） ≥ ｜V（G）｜ for any xy E（G）. Luo et al. [European J. Combin., 2008] characterized the simple Z3-connected graphs satisfying the Ore-condition. In this paper...A graph G satisfies the Ore-condition if d（x）＋d（y） ≥ ｜V（G）｜ for any xy E（G）. Luo et al. [European J. Combin., 2008] characterized the simple Z3-connected graphs satisfying the Ore-condition. In this paper, we characterize the simple Z3-connected graphs G satisfying d（x）＋d（y） ≥ ｜V（G）｜ - 1 for any xy E（G）, which improves the results of Luo et al.展开更多
A cycle C of a graph G is a m-distance-dominating cycle if for all vertices of . Defining denotes the minimum value of the degree sum of any k independent vertices of G. In this paper, we prove that if G is a 3-connec...A cycle C of a graph G is a m-distance-dominating cycle if for all vertices of . Defining denotes the minimum value of the degree sum of any k independent vertices of G. In this paper, we prove that if G is a 3-connected graph on n vertices, and if , then every longest cycle is m-distance-dominating cycles.展开更多
In this paper we determine all the bipartite graphs with the maximum sum of squares of degrees among the ones with a given number of vertices and edges.
This is an expository paper on algebraic aspects of exponential sums over finite fields.This is a new direction.Various examples,results and open problems are presented along the way,with particular emphasis on Gauss ...This is an expository paper on algebraic aspects of exponential sums over finite fields.This is a new direction.Various examples,results and open problems are presented along the way,with particular emphasis on Gauss periods,Kloosterman sums and one variable exponential sums.One main tool is the applications of various p-adic methods.For this reason,the author has also included a brief exposition of certain p-adic estimates of exponential sums.The material is based on the lectures given at the 2020 online number theory summer school held at Xiamen University.Notes were taken by Shaoshi Chen and Ruichen Xu.展开更多
A tree with at most m leaves is called an m-ended tree.Kyaw proved that every connected K1,4-free graph withσ4(G)n-1 contains a spanning 3-ended tree.In this paper we obtain a result for k-connected K1,4-free graphs ...A tree with at most m leaves is called an m-ended tree.Kyaw proved that every connected K1,4-free graph withσ4(G)n-1 contains a spanning 3-ended tree.In this paper we obtain a result for k-connected K1,4-free graphs with k 2.Let G be a k-connected K1,4-free graph of order n with k 2.Ifσk+3(G)n+2k-2,then G contains a spanning 3-ended tree.展开更多
An invariant σ2（G） of a graph is defined as follows： σ2（G） ：= min{d（u） ＋ d（v）｜u, v ∈V（G）,uv ∈ E（G）,u ≠ v} is the minimum degree sum of nonadjacent vertices （when G is a complete graph, we define ...An invariant σ2（G） of a graph is defined as follows： σ2（G） ：= min{d（u） ＋ d（v）｜u, v ∈V（G）,uv ∈ E（G）,u ≠ v} is the minimum degree sum of nonadjacent vertices （when G is a complete graph, we define σ2（G） = ∞）. Let k, s be integers with k ≥ 2 and s ≥ 4, G be a graph of order n sufficiently large compared with s and k. We show that if σ2（G） ≥ n ＋ k- 1, then for any set of k independent vertices v1,..., vk, G has k vertex-disjoint cycles C1,..., Ck such that ｜Ci｜ ≤ s and vi ∈ V（Ci） for all 1 ≤ i ≤ k. The condition of degree sum σs（G） ≥ n ＋ k - 1 is sharp.展开更多
基金Supported by the National Natural Science Foundation of China(11871099).
文摘In this note,we show a sharp lower bound of min{Σ_(i=1)^(k)dG(u_(i)):u1u2...uk is a path of(2-)connected G}on its order such that(k-1)-iterated line graphs L^(k-1)(G)are hamiltonian.
基金Partially supported by the National Natural Sciences Foundation of China (No.19831080).
文摘Abstract A graph g is k-ordered Hamiltonian, 2 h k h n, if for every ordered sequence S of k distinct vertices of G, there exists a Hamiltonian cycle that encounters S in the given order. In this article, we prove that if G is a graph on n vertices with degree sum of nonadjacent vertices at least $n+{{3k - 9} \over 2}$, then G is k-ordered Hamiltonian for k=3,4,...,￠${n \over {19}}$?. We also show that the degree sum bound can be reduced to n+ 2 ￠ ${k \over {2}}$ m 2 if $\kappa(G)\ge {{3k - 1} \over 2}$ or '(G) S 5k m 4. Several known results are generalized.
基金Supported by National Natural Science Foundation of China (Grant No. 11071233)the Fundamental Research Funds for the Central Universities (Grant No. WK0010000021)
文摘A graph G satisfies the Ore-condition if d（x）＋d（y） ≥ ｜V（G）｜ for any xy E（G）. Luo et al. [European J. Combin., 2008] characterized the simple Z3-connected graphs satisfying the Ore-condition. In this paper, we characterize the simple Z3-connected graphs G satisfying d（x）＋d（y） ≥ ｜V（G）｜ - 1 for any xy E（G）, which improves the results of Luo et al.
文摘A cycle C of a graph G is a m-distance-dominating cycle if for all vertices of . Defining denotes the minimum value of the degree sum of any k independent vertices of G. In this paper, we prove that if G is a 3-connected graph on n vertices, and if , then every longest cycle is m-distance-dominating cycles.
基金Supported by the National Natural Science Foundation of China(No.11271300)
文摘In this paper we determine all the bipartite graphs with the maximum sum of squares of degrees among the ones with a given number of vertices and edges.
基金partially supported by the National Natural Science of Foundation under Grant No.1900929。
文摘This is an expository paper on algebraic aspects of exponential sums over finite fields.This is a new direction.Various examples,results and open problems are presented along the way,with particular emphasis on Gauss periods,Kloosterman sums and one variable exponential sums.One main tool is the applications of various p-adic methods.For this reason,the author has also included a brief exposition of certain p-adic estimates of exponential sums.The material is based on the lectures given at the 2020 online number theory summer school held at Xiamen University.Notes were taken by Shaoshi Chen and Ruichen Xu.
基金supported by Scientific Research Fund of Hubei Provincial Education Department (Grant No. Q20141609)National Natural Science Foundation of China (Grant Nos. 11371162 and 11271149)Wuhan Textile University (2012)
文摘A tree with at most m leaves is called an m-ended tree.Kyaw proved that every connected K1,4-free graph withσ4(G)n-1 contains a spanning 3-ended tree.In this paper we obtain a result for k-connected K1,4-free graphs with k 2.Let G be a k-connected K1,4-free graph of order n with k 2.Ifσk+3(G)n+2k-2,then G contains a spanning 3-ended tree.
基金Foundation item： the National Natural Science Foundation of China （No. 10626029）.
文摘An invariant σ2（G） of a graph is defined as follows： σ2（G） ：= min{d（u） ＋ d（v）｜u, v ∈V（G）,uv ∈ E（G）,u ≠ v} is the minimum degree sum of nonadjacent vertices （when G is a complete graph, we define σ2（G） = ∞）. Let k, s be integers with k ≥ 2 and s ≥ 4, G be a graph of order n sufficiently large compared with s and k. We show that if σ2（G） ≥ n ＋ k- 1, then for any set of k independent vertices v1,..., vk, G has k vertex-disjoint cycles C1,..., Ck such that ｜Ci｜ ≤ s and vi ∈ V（Ci） for all 1 ≤ i ≤ k. The condition of degree sum σs（G） ≥ n ＋ k - 1 is sharp.
