# Seminars this week

## Pure Maths Colloquium

## Anitha Thillaisundaram (University of Lincoln)

## Ramification structures for quotients of generalised Grigorchuk-Gupta-Sidki groups

Wednesday, 11 December at 14:00J11

### Abstract

Groups of surfaces isogenous to a higher product of curves can be characterised by a purely group-theoretic condition, which is the existence of a so-called ramification structure. Gul and Uria-Albizuri showed that quotients of the periodic Grigorchuk-Gupta-Sidki groups, GGS-groups for short, admit ramification structures. We extend their result by showing that quotients of generalisations of the GGS-groups also admit ramification structures, with some deviations for the case p=2. This is joint work with Elena Di Domenico and Sukran Gul.

## Algebra / Algebraic Geometry seminar

## Adeel Khan (University of Regensburg)

## Intersection theory of derived stacks

**Wednesday**, 11 December at

**15:00**

**LT-B**

### Abstract

I will discuss how various formalisms of intersection theory (Chow groups, K-theory, cobordism) can be extended to the setting of derived schemes and stacks. This gives a new approach to virtual phenomena such as the virtual fundamental class and virtual Riemann-Roch formulas.

## Cosmology, Relativity and Gravitation

## Theo Torres (University of Sheffield)

## Hydrodynamic simulations of rotating black holes

**Wednesday**, 11 December at

**15:00**

**J11, Hicks**

### Abstract

Wave scattering phenomena are ubiquitous in almost all Sciences, from Biology to Physics. Interestingly, it has been shown many times that different physical systems are the stage to the same processes. One stunning example is the observation that waves propagating on a flowing fluid effectively experience the presence of a curved space-time. In this talk we will use this analogy to investigate, both theoretically and experimentally, fundamental effects occurring around vortex flows and rotating black holes. In particular, we will focus on light-bending, superradiance scattering, and quasi-normal modes emission

## ShEAF: postgraduate pure maths seminar

## Callum Reader

## TBA

Wednesday, 11 December at 16:00J11 Hicks

### Abstract

TBA

## Teaching Lunch

## James Cranch (Sheffield)

## Maths competitions, and the journey from school to university

**Thursday**, 12 December at

**13:00**

**LT6**

### Abstract

This summer, when I wasn't working in SoMaS as normal, I helped run the 60th International Mathematical Olympiad in Bath, and handed in a dissertation for a Masters degree in education. I'd like to talk about what these activities might have to do with one another: I'll speculate a bit about what universities can and should be doing to help school-aged students with their maths.

## Statistics Seminar

## Jeremy Colman (Sheffield)

## Simulation-Based Calibration (SBC)

Thursday, 12 December at 14:00**LT E**

### Abstract

SBC is a relatively new method for checking Bayesian inference algorithms. Its advocates (Talts et al. (2017)) argue that it identifies inaccurate computation and inconsistencies in model implementation and also provides graphical summaries to indicate the nature of the underlying problems. An example of such a summary is given. Although SBC has emerged from the Stan development team it is applicable to any Bayesian model that is capable of generating posterior samples. It does not require the use of any particular modelling language. I shall explain why there might indeed be a gap that SBC could fill, demonstrate how SBC works in practice, and discuss the balance between its costs and benefits.