报告题目1：Packing Steiner Trees in Digraphs

报告人：孙跃方教授，宁波大学

报告时间：2025年9月23日（周二） 9:00-12:00

报告地点：腾讯会议ID：160 481 528

报告摘要：Packing of combinatorial objects such as graphs, digraphs and hypergraphs by smaller objects is one of the central problems in graph theory and combinatorial optimization. The famous Steiner tree packing problem in undirected graphs has become a well-established topic. It is natural to extend this problem to digraphs, and such problems in digraphs are called directed Steiner type packing problems, including directed Steiner tree packing problem and strong subgraph packing problem. In this talk, we introduce known results on the directed Steiner tree packing problem and related topics. This is a joint work with Anders Yeo, Shanshan Yu and Xiaoyan Zhang.

报告人简介： 孙跃方，宁波大学数学与统计学院教授、博士生导师。主持国家自然科学基金2项。出版学术专著1部，发表SCI期刊论文50余篇。当前主要从事有向图理论的研究。

报告题目2：Number of Subgraphs and Their Converses in Tournaments

报告人：雷辉副教授，南开大学

报告时间：2025年9月23日（周二） 9:00-12:00

报告地点：腾讯会议ID：160 481 528

报告摘要：An oriented graph $D$ is {\it converse invariant} if, for any tournament $T$,  the number of copies of  $D$ in $T$ is equal to that of its converse $-D$. El Sahili and Ghazo Hanna [J. Graph Theory 102 (2023), 684-701] showed that any oriented graph $D$ with maximum degree at most 2 is converse invariant. They proposed a question: Can we characterize all converse invariant oriented graphs? In this talk, we introduce a digraph polynomial and employ it to give a necessary condition for an oriented graph to be converse invariant. We characterize all orientations of trees with diameter at most 3 that are converse invariant. In addition, in contrast to the findings of El Sahili and Ghazo Hanna, we prove that every connected graph $G$ with maximum degree at least $3$, admits an orientation $D$ of $G$ such that $D$ is not converse invariant.

This is joint work with Jiangdong Ai, Gregory Gutin, Anders Yeo, Yacong Zhou

报告人简介：雷辉，南开大学统计与数据科学学院副教授、博士生导师。2022年入选第八届中国科协“青年人才托举工程”项目。主要研究领域是图论与组合优化，在Journal of Graph Theory等杂志上发表论文20余篇，主持国家自然科学基金面上、青年各一项，参与国家自然科学基金重点项目一项。

报告题目3：Results on anti-Ramsey numbers of graphs

报告人：兰永新副教授，河北工业大学

报告时间：2025年9月23日（周二） 9:00-12:00

报告地点：腾讯会议ID：160 481 528

报告摘要：Motivated by anti-Ramsey numbers introduced by Erd\H{o}s, Simonovits and S\'os in 1975, we study the anti-Ramsey problem when host graphs are complete split graphs, plane triangulations, maximal outerplanar graphs. Given a positive integer $n$ and a plane graph $H$, let  $\mathcal{G}(H)$  be the family of  graphs $G$ such that $G$  contains  $H$ as a subgraph. The \dfn{ anti-Ramsey number of $H$ with respect to $\mathcal{G}(H)$}, denoted  $ar(\mathcal{G}(H), H)$, is the maximum number $k$ such that no edge-coloring of any graph in $\mathcal{G}(H)$ with $k$ colors contains a rainbow copy of $H$.

In this talk, we will present some results on anti-Ramsey numbers of graph with respect to $\mathcal{G}(H)$, when $\mathcal{G}(H)$ is $\{K_n+\overline{K_s}\}$, the set of all plane triangulations, and the set of all maximal outerplanar graphs. Joint work with Zhongmei Qin, Yongtang Shi, Zi-Xia Song and Changqing Xu.

报告人简介：兰永新，河北工业大学理学院副教授。主要研究方向为极值图论、结构图论等。研究成果在The Electronic of Combinatorics, Discrete Mathematics等SCI期刊发表学术论文20余篇。主持国家自然科学基金青年项目（C类）1项、河北省自然科学基金青年项目（B类、C类）2项，参与国家自然科学基金5项。2019年在南开大学获得博士学位，并入选河北工业大学第四届“元光学者”计划，2021年获河北省数学会青年学术奖，曾赴韩国纽约州立大学、英国皇家霍洛威学院访问。现担任中国运筹学会图论与组合分会青年理事、天津市工业与应用数学学会理事、河北省工业与应用数学学会理事。