Speakers: Prangya Parida, U. Ottawa, and Kiara McDonald, U. Victoria Zoom link:  https://us02web.zoom.us/j/86415230827?pwd=QUxLUnlMdWYzL05zSUJ4bnBCOUJnZz09 --------------------------------------------------- Prangya Parida: Title: Cover-free families on graphs Abstract: A family of subsets of a t-set is called a d-cover-free family if no subset is contained in the union of any d other subsets. We denote by t(d, n) the minimum  t for which there exists a d-cover-free family of a t-set with n subsets. Cover-free families (CFF) have wide applications in combinatorial group testing, where a d-CFF(t, n) can be…

Ramsey numbers of signed graphs Ben Seamone, Dawson College and Université de Montréal Abstract: Nathan Acheampong (Université de Montréal) Francis Clavette (Université de Montréal) Geˇna Hahn (Université de Montréal) Margaux Marseloo (Université Paris-Saclay) Viktor Paardekooper (Université de Montréal), and Ben Seamone* (Dawson College & Université de Montréal) A signed graph is a pair (G, σ) where G = (V,E) is a graph and σ : E(G) → {+, −} is a signature which assigns a sign to each edge of G. One well-studied operation on…

Switching m-edge coloured graphs Speaker: Gary MacGillivray, University of Victoria Abstract: An m-edge-coloured graph consists of a set of vertices, any two of which are either joined by an edge of one of m colours or not joined at all. The operation of switching at a vertex v of an m-edge-coloured graph with respect to an element of a subgroup \Gamma of S_m  permutes the colours of the edges incident with v.  Switching defines an equivalence relation on the set…

Kemeny's constant for Markov chains and random walks on graphs Speaker: Jane Breen, Ontario Tech University Kemeny's constant is an interesting and useful quantifier of how well-connected the states of a Markov chain are. Though it was first introduced in the 1960s, interest in this concept has recently exploded. This talk will provide an introduction to Markov chains, an overview of the history of Kemeny’s constant, discussion of some applications, and a survey of recent results, with an emphasis on…

Time: 3:30 pm, Atlantic time, (4:00 pm NST) Wednesday, Feb. 12 Speaker: Robert Bailey, Memorial University Title: Computer constructions of distance-regular graphs with primitive automorphism groups Abstract: A graph is distance-regular if, for each vertex $v$ and each vertex $w$ at distance $i$ from $v$, the number of neighbours of $w$ at distances $i-1$, $i$ or $i+1$ from $v$ depends only on $i$, and not on the choice of $v$ or $w$.  These are highly-structured graphs with interesting structural and…

Speaker: Karen Meagher, University of Regina Title: Derangement graphs and the intersection density of permutation groups Abstract: Two permutations are intersecting if they both map some $i$ to the same point, equivalently, permutations $\sigma$ and $\pi$ are intersecting if and only if $\pi^{-1}\sigma$ has a fixed point. A set of permutations is called intersecting if any two permutations in the set are intersecting. For any transitive group the stabilizer of a point is an intersecting set. The intersection density of a permutation…

Time: 3:30 pm, Atlantic time, (2:30 pm EST) Wednesday, Mar. 12 Speaker: Ron Gould, Emory University Title: Looking for Saturation in all Kinds of Places Abstract: Given a graph $H$, a graph $G$ is $H$-saturated if $G$ does not contain $H$ as a subgraph, but the addition of any missing edge to $G$ results in a graph containing $H$ as a subgraph. An $H$-saturated graph with the maximum number of edges is called an extremal graph for $H$ and for…

The 2-burning number of a graph Speaker: Ann Trenk, Wellesley College Abstract: We discuss a discrete-time model for the spread of information in a graph, motivated by the idea that people believe a story when they learn of it from two different origins. Similar to the burning number, in this problem, information spreads in rounds and a new source can appear in each round. For a graph $G$, we are interested in $b_2(G)$, the minimum number of rounds until the…