Mon, 13 Oct 2025
16:00
C3

Eigenvalues of non-backtracking matrices

Cedric Pilatte
(Mathematical Insitute, Oxford)
Abstract
Understanding the eigenvalues of the adjacency matrix of a (possibly weighted) graph is a problem arising in various fields of mathematics. Since a direct computation of the spectrum is often too difficult, a common strategy is to instead study the trace of a high power of the matrix, which corresponds to a high moment of the eigenvalues. The utility of this method comes from its combinatorial interpretation: the trace counts the weighted, closed walks of a given length within the graph.
 
However, a common obstacle arises when these walk-counts are dominated by trivial "backtracking" walks—walks that travel along an edge and immediately return. Such paths can mask the more meaningful structural properties of the graph, yielding only trivial bounds.
 
This talk will introduce a powerful tool for resolving this issue: the non-backtracking matrix. We will explore the fundamental relationship between its spectrum and that of the original matrix. This technique has been successfully applied in computer science and random graph theory, and it is a key ingredient in upcoming work on the 2-point logarithmic Chowla conjecture.
Tue, 21 Oct 2025
12:30
C3

Mathematical modelling of a mass-conserving electrolytic cell

Georgina Ryan, OCIAM
Abstract

The electrochemical processes in electrolytic cells are the basis for modern energy technology such as batteries. Electrolytic cells consist of an electrolyte (an salt dissolved in solution), two electrodes, and a battery. The Poisson–Nernst–Planck equations are the simplest mathematical model of steady state ionic transport in an electrolytic cell. We find the matched asymptotic solutions for the ionic concentrations and electric potential inside the electrolytic cell with mass conservation and known flux boundary conditions. The mass conservation condition necessitates solving for a higher order solution in the outer region. Our results provide insight into the behaviour of an electrochemical system with a known voltage and current, which are both experimentally measurable quantities.

Mon, 01 Dec 2025
16:00
C3

TBC

Søren Eilers
(Unviersity of Copenhagen)
Abstract

to follow

Thu, 20 Nov 2025
16:00
C3

TBC

Marius Dadarlat
(Purdue)
Abstract

to follow

Tue, 30 Sep 2025
15:00
C3

Spacetime reconstruction and measured Lorentz-Gromov-Hausdorff convergence

Mathias Braun
(École Polytechnique Fédérale de Lausanne (EPFL))
Abstract

We present Gromov's celebrated reconstruction theorem in Lorentzian geometry and show two applications. First, we introduce several notions of convergence of (isomorphism classes of) normalized bounded Lorentzian metric measure spaces, for which we describe several fundamental properties. Second, we state a version within the spacetime reconstruction problem from quantum gravity. Partly in collaboration with Clemens Sämann (University of Vienna).

Tue, 11 Nov 2025
16:00
C3

TBC

Ghazaleh Asghari
(University of Reading)
Abstract

to follow

Tue, 04 Nov 2025
16:00
C3

TBC

Aaron Kettner
(Institute of Mathematics, Czech Academy of Sciences)
Abstract

to follow

Tue, 21 Oct 2025
16:00
C3

TBC

Julian Gonzales
(University of Glasgow)
Abstract

to follow

Tue, 28 Oct 2025
16:00
C3

TBC

Sophie Zegers
(TU Delft)
Abstract

to follow

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