Dalhousie-AARMS AAMP Seminar: Jared Wunsch (Northwestern University)
2021-03-26 16:00 - 17:00 (America/Halifax) | Zoom seminar
The Dalhousie-AARMS Analysis-Applied Math-Physics Seminar takes place on Fridays from 4 – 5 pm Atlantic Time over Zoom. If you would like to attend, please email the organizers for connection details.

Atlantic Graph Theory Seminar: Dr Danielle Cox, Mount Saint Vincent University
2021-03-24 15:30 - 16:30 UTC
The Atlantic Graph Theory Seminar series will take place every Wednesday from 3:30-4:30 ADT online via zoom. The talks, provided by researchers, postdocs and graduate students, will be on a variety of current topics in graph theory. If you would like to give a talk or attend, please email one of the organizers (Jason Brown and Danielle Cox).

Dalhousie-AARMS AAMP Seminar: Marco Merkli (MUN)
2021-03-19 16:00 - 17:00 (America/Halifax)

Atlantic Graph Theory Seminar: Dr Peter Danziger, Ryerson University
2021-03-17 15:30 - 16:30 UTC

AARMS COVID-19 Seminar: Ting-Hao Hsu (UNB)
2021-03-17 10:30 - 11:30 (America/Halifax)
Slow-Fast Systems in Epidemic Models
Differential equations involving slow and fast time scales have been adopted in mathematical modelling to capture rapid changes occurred in the epidemic systems. Examples include outbreaks of infectious diseases and autonomous behavioural changes of individuals. I will introduce a new technic in slow-fast systems to analyze relaxation oscillations, i.e., periodic orbits with slow and fast segments, in such models. The approach is based on extending the so-called entry-exit function to multi-dimensional slow-fast systems using the geometric singular perturbation theory.
This is a virtual zoom seminar. If you would like to attend, please email the organizers for connection details. All times are given in the Atlantic timezone.

Dalhousie-AARMS AAMP Seminar: François Monard (U. California, Santa Cruz)
2021-03-12 16:00 - 17:00 (America/Halifax)

Atlantic Graph Theory Seminar: Dr Nancy Clarke, Acadia University
2021-03-10 15:30 - 16:30 UTC

Dalhousie-AARMS AAMP Seminar: Steven Lester (King's College London)
2021-03-05 16:00 - 17:00 (America/Halifax)

Atlantic Graph Theory Seminar: Dr Jeannette Janssen, Dalhousie University
2021-03-03 15:30 - 16:30 UTC

AARMS COVID-19 Seminar: James Watmough (UNB)
2021-03-03 10:30 - 11:30 (America/Halifax)
Case importation and community spread: post-pandemic control of the spread of SARS-CoV-2 in low density populations
It has been just over one year and 100 million cases since we first heard of a novel coronavirus with pandemic potential. We are now all far too familiar with epidemic curves and would very much like to see the tail of this one. In this talk, I will review the simple mathematical models for the transition from pandemic to endemic and what they tell us about this tail.
For the past year, Canada has kept case numbers relatively low through a combination of community quarantine and travel restrictions. In theory, this has implications for how we approach and manage the new normal of endemic SARS-CoV-2. I will focus on what this might mean for Atlantic Canada.
This is a virtual zoom seminar. If you would like to attend, please email the organizers for connection details. All times are given in the Atlantic timezone.

Atlantic Graph Theory Seminar: Dr. Gary Gordon, Lafayette College
2021-02-24 15:30 - 16:30 UTC
Permutations of finite subsets of R^2 generated by Euclidean distances
Given a finite set of points S = {P1, P2, . . . , Pn} and a vantage point V, generate an ordering of the points of S by measuring the Euclidean distance from V to each of the points of S, ordering them from nearest to farthest. As the vantage point moves around the plane, different orderings will be generated. We are interested in the maximum, minimum, and intermediate values achievable for different point-sets S. (Good and Tideman solved the maximum problem in all dimensions in the 1970s.) We also consider a generalization that uses two vantage points, using the average distance (d(V1, Pk) + d(V2, Pk))/2 to the points of S to generate an ordering.
The Atlantic Graph Theory Seminar series will take place every Wednesday from 3:30-4:30 ADT online via zoom. The talks, provided by researchers, postdocs and graduate students, will be on a variety of current topics in graph theory. If you would like to give a talk or attend, please email one of the organizers (Jason Brown and Danielle Cox).

Atlantic GR Seminar: Sarah Muth (MUN)
2021-02-24 13:00 - 14:00 (America/Halifax)
Marginally Outer Trapped (Open) Surfaces in 4+1 Dimensional Schwarzschild
In the case of binary black hole mergers, the surface of most obvious interest, the Event Horizon, is often computationally difficult to locate. Instead, it is useful to turn to quasi-local characterizations of black hole boundaries, such as Marginally Outer Trapped Surfaces (MOTS), which are defined for a single time slice of the spacetime, and the outer-most of which is the apparent horizon. In this talk, I will describe ongoing work focused on understanding MOTS in the interior of a five-dimensional Schwarzschild black hole. Similar to the four-dimensional case previously studied, we find examples of self-intersecting MOTS with an arbitrary number of self-intersections. This provides further support that self-intersecting behavior is rather generic. I will also briefly discuss the next stage of our research, which involves further examples of these self-intersecting MOTS, this time in the full Kruskal extension of Schwarzschild.
The Atlantic General Relativity 2020 online postdoc/student seminar series is in the tradition of the annual AGR meetings, providing a forum not only for students and postdocs to present their research and make professional contacts but also to facilitate connections and collaborations between all Atlantic Canadian relativists. The series is student-organized and includes all areas of classical and quantum gravity. Talks will occur on the last Wednesday of every month, with each session consisting of two 30 minute talks. If you would like to attend, please email the organizers for connection details.
Note: all times are Atlantic Time

AARMS COVID-19 Seminar: JC Loredo-Osti (Memorial)
2021-02-17 10:30 - 11:30 (America/Halifax)
Covid-19 management in Newfoundland and Labrador
Atlantic Canada and the territories have experienced a qualitatively different COVID-19 epidemic than the other Canadian provinces. The question is, do these differences suggest different best approaches to public health policy or they are just the consequence of geographic/demographic conditions? When infection prevalence is low, imported infections are not only a large fraction of all infections, but a major trigger of outbreaks. This also posses questions about the merits of travel restrictions as well as the escalation of measures in response to outbreaks. On this presentation, we will discuss some of the ways to quantify these issues in the context of the pandemic in Atlantic Canada, and in particular in Newfoundland and Labrador.
This is a virtual zoom seminar. If you would like to attend, please email the organizers for connection details. All times are given in the Atlantic timezone.

Atlantic Graph Theory Seminar: Dr Anthony Bonato, Ryerson University
2021-02-10 15:30 - 16:30 UTC
The localization game played on graph
Graph searching investigates combinatorial models for the detection or neutralization of an adversary’s activity on a network. One such model is the localization game, where pursuers use distance probes to capture an invisible evader. We present new results on the localization number of a graph, which is the minimum number of pursuers needed to capture the evader. We survey what is known and unknown for the localization number, discuss connections with the chromatic number, and give bounds on graph families such as hypercubes, incidence graphs of combinatorial designs, and Kneser graphs.
The Atlantic Graph Theory Seminar series will take place every Wednesday from 3:30-4:30 ADT online via zoom. The talks, provided by researchers, postdocs and graduate students, will be on a variety of current topics in graph theory. If you would like to give a talk or attend, please email one of the organizers (Jason Brown and Danielle Cox).

AARMS COVID-19 Seminar: Sanjeev Seahra (UNB)
2021-02-03 10:30 - 11:30 (America/Halifax)
COVID-19 modelling in New Brunswick and elsewhere
We present a simple differential equation based model of the COVID-19 pandemic that allows for time-evolving social distancing. We apply the model to the first 80 days of the pandemic in 24 different jurisdictions to quantify the effectiveness of government lockdowns in March 2020. Using Bayesian methods, we then estimate model parameters relevant to the current outbreak in New Brunswick.
This is a virtual zoom seminar. If you would like to attend, please email the organizers for connection details. All times are given in the Atlantic timezone.

Dalhousie-AARMS AAMP Seminar: Alan Lindsay (Notre Dame)
2021-01-29 16:00 - 17:00 (America/Halifax)

Atlantic Graph Theory Seminar: Jordan Barrett, PhD Candidate, McGill University
2021-01-27 15:30 - 16:30 UTC

Dalhousie-AARMS AAMP Seminar: Allan Greenleaf (Rochester)
2021-01-22 16:00 - 17:00 (America/Halifax)

Atlantic Graph Theory Seminar: Dr. Hugh Thomas, UQAM
2021-01-20 15:30 - 16:30 UTC
Dynamical algebraic combinatorics and independence sets of graphs
Dynamical algebraic combinatorics is a relatively new (and fun!) topic, which looks at cyclic group actions on objects from algebraic combinatorics, inspired by some questions coming from dynamical systems. I will give an introduction to the area, focusing on an action I have defined with Nathan Williams on the independent sets of a graph (arXiv:1805.00815). We also construct a partial order on the set of independent sets of a graph, which may be of independent interest.
The Atlantic Graph Theory Seminar series will take place every Wednesday from 3:30-4:30 ADT online via zoom. The talks, provided by researchers, postdocs and graduate students, will be on a variety of current topics in graph theory. If you would like to give a talk or attend, please email one of the organizers (Jason Brown and Danielle Cox).

Atlantic Graph Theory Seminar: Dr Stephen Finbow, Saint Francis Xavier University
2021-01-13 15:30 - 16:30 UTC
The γ-graph of a graph
For a graph G = (V, E), the γ-graph of G, G(γ) = (V (γ), E(γ)), is the reconfiguration graph whose vertex set is the collection of minimum dominating sets, or γ-sets of G, and two γ-sets are adjacent in G(γ) if they differ by a single vertex and the two different vertices are adjacent in G. The γ-graph of G was introduced by Fricke et al. in 2011 where they studied properties of γ-graphs, and raised seven questions. In this seminar we will discuss the study of γ-graphs to date with a focus on the progress of these questions.
The Atlantic Graph Theory Seminar series will take place every Wednesday from 3:30-4:30 ADT online via zoom. The talks, provided by researchers, postdocs and graduate students, will be on a variety of current topics in graph theory. If you would like to give a talk or attend, please email one of the organizers (Jason Brown and Danielle Cox).

AARMS COVID-19 Seminar: Ali Gharouni (McMaster)
2020-12-16 15:00 - 16:30 (America/Halifax)
COVID-19 Outbreak Dynamics and Testing-Isolation Efficacy; Insights from a Simple Epidemic Model
One of the main challenges in understanding COVID-19 dynamics is to estimate changes in the total level of infection in a population. The daily case count is a highly accessible form of data where observations are driven by two types of processes: (i) epidemic processes and (ii) testing processes. The challenge is then to separate these processes and understand how they interact. We developed a model that incorporates mechanistic processes of epidemic processes and testing. We have used the model to study the potential
effect of testing strategies on disease dynamics. In future work, we will develop improved methods for estimating true incidence by using data from negative as well as positive tests.
In collaboration with: Fady Abdelmalek and Drs Benjamin M Bolker, Jonathan Dushoff, David JD Earn
This is a virtual zoom seminar. If you would like to attend, please email the organizers for connection details. All times are given in the Atlantic timezone.

Atlantic Graph Theory Seminar: Dr Erin Meger (Université du Québec à Montréal)
2020-12-09 15:30 - 16:30 UTC
The Iterated Local Model for Social Networks
Complex networks are said to exhibit four key properties: large scale, evolving over time, small world properties, and power law degree distribution. The Preferential Attachment Model (Barab´asi–Albert, 1999) and the ACL Preferential Attachment Model (Aiello, Chung, Lu, 2001) for random networks, evolve over time and rely on the structure of the graph at the previous time step. Further models of complex networks include: the Iterated Local Transitivity Model (Bonato, Hadi, Horn, Pralat, Wang, 2011) and the Iterated Local Anti-Transitivity Model (Bonato, Infeld, Pokhrel, Pralat, 2017). In this talk, we will define and discuss the Iterated Local Model. This is a generalization of the ILT and ILAT models, where at each time step edges are added deterministically according to the structure of the graph at the previous time step.
The Atlantic Graph Theory Seminar series will take place every Wednesday from 3:30-4:30 ADT online via zoom. The talks, provided by researchers, postdocs and graduate students, will be on a variety of current topics in graph theory. If you would like to give a talk or attend, please email one of the organizers (Jason Brown and Danielle Cox).

Dalhousie-AARMS AAMP Seminar: Peter Hintz (MIT)
2020-12-04 16:00 - 17:00 (America/Halifax)
Title: Linear stability of slowly rotating Kerr spacetimes
Abstract: I will describe joint work with Dietrich Häfner and András Vasy in which we study the asymptotic behavior of linearized gravitational perturbations of Schwarzschild or slowly rotating Kerr black hole spacetimes. We show that solutions of the linearized Einstein equation decay at an inverse polynomial rate to a stationary solution (given by an infinitesimal variation of the mass and angular momentum of the black hole), plus a pure gauge term. The proof uses a detailed description of the resolvent of an associated wave equation on symmetric 2-tensors near zero energy.
The Dalhousie-AARMS Analysis-Applied Math-Physics Seminar takes place on Fridays from 4 – 5 pm Atlantic Time over Zoom. If you would like to attend, please email the organizers for connection details.

Atlantic Graph Theory Seminar: Dr Melissa Huggan (Ryerson University)
2020-12-02 15:30 - 16:30 UTC
The Cheating Robot and Insider Information
Throughout this talk, we explore a deterministic model as an alternative approach to studying simultaneous play combinatorial games. We call this the Cheating Robot model. This model forces both players to move at the same time, but one player has extra information about where their opponent is going to move and can react accordingly. We discuss some general theory and explore a case study to get some insight into this model. This is joint work with Richard J. Nowakowski.
The Atlantic Graph Theory Seminar series will take place every Wednesday from 3:30-4:30 ADT online via zoom. The talks, provided by researchers, postdocs and graduate students, will be on a variety of current topics in graph theory. If you would like to give a talk or attend, please email one of the organizers (Jason Brown and Danielle Cox).

Dalhousie-AARMS AAMP Seminar: Graham Cox (Memorial University)
2020-11-27 16:00 - 17:00 (America/Halifax)
Title: Nodal deficiency via equipartition energy functionals and the Dirichlet-to-Neumann map
Abstract: A classic result in differential equations is that the nth eigenfunction
of a Sturm-Liouville boundary value problem has precisely n-1 zeros.
Courant’s nodal domain theorem provides a natural generalization of this
result to higher dimensions, but it is generally not sharp. The lack of
sharpness is measured by the “nodal deficiency” of an eigenfunction.
Despite over a century of intensive study, this quantity is still not
very well understood.
The first explicit formula for the nodal deficiency was obtained in 2012
by Berkolaiko, Kuchment and Smilansky, using an energy functional
defined on the space of equipartitions. More recently, with Jones and
Marzuola, I obtained another formula for the nodal deficiency, in terms
of Dirichlet-to-Neumann operators defined on the eigenfunction’s nodal
domains. While originally derived using symplectic methods, this result
can also be understood using the spectral flow generated by a family of
boundary conditions imposed on the nodal set. In this talk I will
describe this flow, and explain how it provides a concrete mechanism by
which low energy eigenfunctions do or do not contribute to the nodal
deficiency. I will also describe recent progress relating these two
formulas for the nodal deficiency, and hint at some applications to the
theory of spectral minimal partitions.
This talk represents joint work with Thomas Beck, Gregory Berkolaiko,
Isabel Bors, Yaiza Canzani, Grace Conte, Christopher Jones and Jeremy
Marzuola.
The Dalhousie-AARMS Analysis-Applied Math-Physics Seminar takes place on Fridays from 4 – 5 pm Atlantic Time over Zoom. If you would like to attend, please email the organizers for connection details.

Atlantic Graph Theory Seminar: Dr Jared Howell (Memorial University of Newfoundland, Grenfell Campus)
2020-11-25 15:30 - 16:30 UTC
Gracefully labelling windmills using Skolem-like sequences
To gracefully label a graph G, assign each vertex v ∊ V(G) a distinct label l(v) from {0,1,2,…,|E(G)|}, such that {|l(u)-l(v)| : uv ∊ E(G)}={1,2,3,…,|E(G)|}. In this talk we will examine constructive techniques using Skolem-like sequences to gracefully label windmills of cycles. This includes new constructive techniques for known results as well as new results on windmills with vanes of mixed cycle length.
The Atlantic Graph Theory Seminar series will take place every Wednesday from 3:30-4:30 ADT online via zoom. The talks, provided by researchers, postdocs and graduate students, will be on a variety of current topics in graph theory. If you would like to give a talk or attend, please email one of the organizers (Jason Brown and Danielle Cox).

Atlantic GR Seminar: Jinzhao Wang (ETH Zurich) and Saikat Mondal (MUN)
2020-11-25 13:00 - 14:00 (America/Halifax)
Outer entropy equals Bartnik-Bray inner mass, and the gravitational ant conjecture
Jinzhao Wang (ETH Zurich)
Entropy and energy are found to be closely tied on our quest for quantum gravity. We point out an interesting connection between the recently proposed outer entropy, a coarse-grained entropy defined for a compact spacetime domain motivated by the holographic duality, and the Bartnik-Bray quasilocal mass long known in the mathematics community. In both scenarios, one seeks an optimal spacetime fill-in of a given closed, connected, spacelike, codimension-two boundary. We show that for an outer-minimizing mean-convex surface, the Bartnik-Bray inner mass matches exactly with the irreducible mass corresponding to the outer entropy. The equivalence implies that the area laws derived from the outer entropy are mathematically equivalent as the monotonicity property of the quasilocal mass. It also gives rise to new bounds between entropy and the gravitational energy, which naturally gives the gravitational counterpart to Wall’s ant conjecture. We also observe that the equality can be achieved in a conformal flow of metrics, which is structurally similar to the Ceyhan-Faulkner proof of the ant conjecture. We compute the small sphere limit of the outer entropy and it is proportional to the bulk stress tensor as one would expect for a quasilocal mass.
Marginally outer trapped (open) surfaces in Schwarzschild geometry and extreme mass ratio merger
Saikat Mondal (MUN)
Black holes are one of the common objects in astrophysics. Some are formed from a dying star, called a stellar black hole. There are also supermassive black holes consisting of mass millions or even billions times that of the sun. Such black holes are thought to lie at the center of almost every galaxy. In this talk we will explore the evolution of horizons of black hole mergers in a special limit called the ” extreme mass ratio” limit. For example, a supermassive black hole merges with a stellar black hole to become a single black hole. In this limit, the merging horizons can be studied with the help of simple numerics. We will discuss mainly about marginally outer trapped surfaces (MOTS). Interestingly, the MOTSs we find in our numerical analysis have an arbitrary number of self-intersections.
The Atlantic General Relativity 2020 online postdoc/student seminar series is in the tradition of the annual AGR meetings, providing a forum not only for students and postdocs to present their research and make professional contacts but also to facilitate connections and collaborations between all Atlantic Canadian relativists. The series is student-organized and includes all areas of classical and quantum gravity. Talks will occur on the last Wednesday of every month, with each session consisting of two 30 minute talks. If you would like to attend, please email the organizers for connection details.

Atlantic Graph Theory Seminar: Kyle MacKeigan (PhD Candidate, Dalhousie University)
2020-11-18 15:30 - 16:30 UTC
Orthogonal Colourings of Graphs
Two colourings of a graph are orthogonal if they have the property that when two vertices receive the same colour in one colouring, then those vertices receive distinct colours in the other colouring. In this talk, the importance of perfect orthogonal colourings is demonstrated. Then, perfect orthogonal colourings of Cayley graphs and tree graphs are constructed. To conclude, it is shown how the Cartesian, tensor, and strong graph product can be used to generate perfect orthogonal colourings.
The Atlantic Graph Theory Seminar series will take place every Wednesday from 3:30-4:30 ADT online via zoom. The talks, provided by researchers, postdocs and graduate students, will be on a variety of current topics in graph theory. If you would like to give a talk or attend, please email one of the organizers (Jason Brown and Danielle Cox).

AARMS COVID-19 Seminar: Shannon LeBlanc (Dept of Health NB)
2020-11-18 15:00 - 16:30 (America/Halifax)
Importation Risk under the Northern Lights
To understand the risk that an infectious traveler from other Canadian provinces and territories will enter the Northwest Territories the Government of the Northwest Territories has fitted jurisdictional reported COVID-19 transmission data to a simple SEIR model. Using the most recent epidemiological parameters for transmission we estimate the likelihood that a pre-symptomatic or asymptomatic/unreported COVID-19 case will travel to the NWT at time t. We have mapped territorial travel data collected since May 2020 to identify the points in time that our importation risk was highest. Using the output of the importation risk model we have developed a Markov tree to assist public health decision makers in understanding the risk that these travelers pose to the public based on the testing and quarantine strategies that they choose to apply.
Shannon LeBlanc is currently an Epidemiologist at the New Brunswick Department of Health who has recently worked with the government of the Northwest Territories
This is a virtual zoom seminar. If you would like to attend, please email the organizers for connection details.

Dalhousie-AARMS AAMP Seminar: Reem Yassawi (Open University, London)
2020-11-06 16:00 - 17:00 (America/Halifax)
Title: Some tame or wild Cantor dynamical systems
Abstract: A topological dynamical system is a pair where is a compact metric spaces and is a group or semigroup acting continuously on . One algebraic invariant of a such a dynamical system is the Ellis semigroup. The Ellis semigroup of a topological dynamical system is defined to be the compactification of the action in the topology of pointwise convergence on the space of all function . Tameness is a concept whose roots date back to Rosenthal’s embedding theorem, which says that if a sequence in does not have a weakly Cauchy subsequence, then it must be a sequence on unit vectors in . Köhler linked the concept of tameness to the Ellis semigroup. A system is tame if its Ellis semigroup has size at most the continuum. Non-tame systems are very far from tame, as they must contain a copy of , the Stone-Cech compactification of .
In this talk, I will briefly survey the properties of the Ellis semigroup that make it an interesting object to study, and discuss recent developments concerning tameness. I will then discuss Toeplitz shifts, which themselves have been studied extensively in this context and is the subject of some joint work with G. Fuhrmann and J. Kellendonk.
The Dalhousie-AARMS Analysis-Applied Math-Physics Seminar takes place on Fridays from 4 – 5 pm Atlantic Time over Zoom. If you would like to attend, please email the organizers for connection details.
