# Seminars this semester

Series:

 Sep 26 Wed Yang Zhang (Sheffield (Mech Eng)) Applied Mathematics Colloquium 14:00 Hicks, LT 9 Imaging based flame diagnostics and its quantitative analysis Abstract: In this talk, a brief history of photography and their application in combustion studies will be given, which actually goes back to the 19th century. Then case studies will be shown on digital flame imaging, especially high speed imaging for the tracking of the fast flame dynamics. It will demonstrate that selective digital imaging enhancement is essential in observing the drastically different flame light intensities of the soot and chemical species. Through digital image processing, quantitative and useful information can be extracted from the flame image database. The simultaneous imaging of visible and infrared light emissions from the ignition of a flame using a single high speed colour digital camera will also be demonstrated which also poses a challenge in spectroscopic study on how to identify this infrared only emissions. Oct 1 Mon Rachel Bearon (Liverpool) Mathematical Biology Seminar Series 14:00 Hicks F41 Revisiting Jeffery orbits; the importance of shape for micro-organism transport Oct 3 Wed Priya Subramanian (Leeds) Applied Mathematics Colloquium 14:00 Hicks, LT 9 Pattern formation in systems with multiple scales Oct 9 Tue Angelo Rendina (Sheffield) Number Theory seminar 14:00 J11 Nearly holomorphic Siegel modular forms and applications Abstract: Nearly holomorphic modular forms were introduced by Shimura as a generalization of modular forms to study a more general class of Eisenstein series. I will introduce some of the tools that we use to work with them, such as the Shimura-Maass differential operator and holomorphic projection, and present some applications: some formulae for the sum of divisor $s_r$ and Ramanujan $\tau$ functions and then congruences of critical $L$-values attached to Siegel modular forms, the latter being part of my research project. Oct 15 Mon Helen Kettle (BIOSS) Mathematical Biology Seminar Series 14:00 Hicks F41 Oct 16 Tue Kohei Kikuta (Osaka) Algebra / Algebraic Geometry seminar 16:00 J11 On categorical entropy Abstract: The categorical entropy of triangulated endofunctors was defined by Dimitrov-Haiden-Katzarkov-Kontsevich motivated by classical dynamical theory. In this talk, I'll explain relations to classical entropy theory, basics on categorical entropy, many examples and future directions. Oct 17 Wed Kevin Buzzard (Imperial) Pure Maths Colloquium 14:00 Hicks Lecture Theatre C Pure mathematics in crisis? Abstract: I argue that pure mathematics is walking inexorably towards a cliff edge, and that anyone who believes that current pure mathematics is rigorous, or a science, needs to wake up and look at the facts, which there will be plenty of in this talk, and they are not pretty. Are our results reproducible? Does it matter? What *is* mathematics? Can computer scientists save us? Can *undergraduates* save us? I hope so. This talk is about pure mathematics but will be accessible to undergraduates, mathematicians both pure and applied/applicable and computer scientists. Oct 18 Thu Gary Verth (Sheffield) Plasma Dynamics Group 15:00 Room K14 (Hicks Building) Introduction to the Sun Abstract: This talk will be an introduction to the science required to understand the Sun and its atmosphere. It is primarily intended for students starting their postgraduate research in plasma, solar, or magnetospheric physics. Due to the introductory nature of the talk, it would also be suitable for any interested non-specialists. Oct 18 Thu Simon Willerton (Sheffield) Topology seminar 16:00 J11 The Legendre-Fenchel transform from a category theoretic perspective Abstract: The Legendre-Fenchel transform is a classical piece of mathematics with many applications. In this talk I'll show how it arises in the context of category theory using categories enriched over the extended real numbers $\overline{ \mathbb{R}}:=[-\infty,+\infty]$. It turns out that it arises out of nothing more than the pairing between a vector space and its dual in the same way that the many classical dualities (eg. in Galois theory or algebraic geometry) arise from a relation between sets. I will assume no knowledge of the Legendre-Fenchel transform and no knowledge of enriched categories. Oct 23 Tue Kim Klinger-Logan (Minnesota) Number Theory seminar 14:00 J11 The Riemann Hypothesis and periods of Eisenstein series Abstract: This summer at Perspectives on the Riemann Hypothesis, Bombieri and Garrett discussed modifications to the invariant Laplacian $\Delta=y^2(\partial_x^2+\partial_y^2)$ on $SL_2(\mathbb{Z})\backslash\mathfrak{H}$ possibly relevant to RH. We will present a $GL(2)$ $L$-function as a period of Eisenstein series which can, in turn, be thought of as a linear functional on an Eisenstein series and we will discuss how such functionals may be use to analyze the zeros of the $L$-function. This idea is an extension of recent work of Bombieri and Garrett and uses techniques from functional analysis and spectral theory of automorphic forms. Oct 24 Wed Christian Voigt (Glasgow) Pure Maths Colloquium 14:00 J11 $C^*$-algebras, the Baum-Connes conjecture and quantum groups Abstract: A central theme of research in operator algebras is the Baum-Connes conjecture, which predicts the K-theory of group $C^*$-algebras and crossed products. In this talk I will give a leisurely introduction to this conjecture, explain what it is good for, and discuss some recent connections with the theory of quantum groups. Oct 24 Wed Istvan Cziegler (York) Applied Mathematics Colloquium 14:00 Hicks, LT 11 Turbulence and phase transitions in tokamak plasmas Abstract: The transition from the low- to the high-confinement operation is one of the most important phenomena in magnetic confinement fusion. The high-confinement regime, known as H-mode, leads to a vastly increased plasma density and temperature, which equates to a significant gain in fusion power. Since the dominant transport across the confining magnetic field is due to turbulence, the L-H transition can be thought of as a phase transition to suppressed turbulence. It is known that both the quality of global confinement and the threshold of the transition depend on macroscopic parameters, such as plasma density, magnetic topology and geometry near particle exhaust areas called divertors. The talk will connect the various scales of dynamics with this phenomenology and some broader context in physics. Oct 24 Wed James Brotherston, Callum Reader, Sadiah Zahoor ShEAF: postgraduate pure maths seminar 16:00 J11 Hicks Oct 25 Thu Anna Marie Bohmann (Vanderbilt) Topology seminar 16:00 J11 Graded Tambara Functors Abstract: Let G be a finite group. The coefficients of G-equivariant cohomology theories naturally form a type of structure called a Mackey functor, which incorporates data coming from each subgroup of G. When the cohomology theory is a G-ring commutative spectrum---meaning that is has an equivariant multiplication---interesting new structures arise. In particular, work of Brun and of Strickland shows that the zeroth homotopy groups have norm maps which yield the structure of a Tambara functor. In this talk, I discuss joint work with Vigleik Angeltveit on the algebraic structure induced by norm maps on the higher homotopy groups, which we call a graded Tambara functor. Oct 29 Mon Elaine Ferguson (Glasgow) Mathematical Biology Seminar Series 14:00 Hicks F41 Oct 30 Tue Adel Betina (Sheffield) Number Theory seminar 14:00 J11 On the p-adic periods of semi-stable modular curves Oct 31 Wed Miguel Teixeira (Reading) Applied Mathematics Colloquium 14:00 Hicks, LT 9 A physically-based model for the wind-driven current in the wavy oceanic surface layer Abstract: A simple analytical model is developed for the current induced by the wind and modified by surface wind-waves in the oceanic surface layer, based on a first-order turbulence closure and including the effect of a vortex force representing the Stokes drift of the waves. The shear stress is partitioned between a component due to shear in the current and a wave-induced component, which decays over a depth proportional to the wavelength. The model reproduces the apparent reduction of the friction velocity and enhancement of the roughness length estimated from current profiles, detected in a number of studies. The current profile becomes flatter for strong wave forcing owing to a smaller fraction of the total shear stress being supported by the current shear. These effects are entirely attributed to non-breaking surface waves, and predicted to increase with wave forcing. A version of the model where the shear stress decays to zero with depth is able to adequately predict the surface current speed. Nov 1 Thu Markus Szymik (NTNU) Topology seminar 16:00 J11 Quandles, knots, and homotopical algebra Abstract: Knots and their groups are a traditional topic of geometric topology. In this talk I will explain how aspects of the subject can be approached using ideas from Quillen’s homotopical algebra, rephrasing old results and leading to new ones. Nov 6 Tue Vlad Serban (Vienna) Number Theory seminar 14:00 J11 A finiteness result for families of Bianchi modular forms Abstract: We develop a p-adic "unlikely intersection” result and show how it can be used to examine which Hida families over imaginary quadratic fields interpolate a dense set of modular forms for GL2 over an imaginary quadratic field. In this way we arrive at the first proven examples where only finitely many classical automorphic forms are on a p-adic family. Nov 12 Mon George Constable (Bath) Mathematical Biology Seminar Series 14:00 Hicks LT10 Nov 13 Tue TBA Number Theory seminar 14:00 J11 Nov 14 Wed Lukasz Grabowski (Lancaster) Pure Maths Colloquium 14:00 J11 Nov 14 Wed James McLaughlin (Northumbria) Applied Mathematics Colloquium 14:00 Hicks, LT 9 Nov 20 Tue Ciaran Schembri (Sheffield) Number Theory seminar 14:00 J11 TBA Nov 21 Wed Tobias Berger (Sheffield) Pure Maths Colloquium 14:00 J11 Nov 21 Wed Simon Malham (Herrot-Watt) Applied Mathematics Colloquium 14:00 Hicks, LT 9 Nov 26 Mon Elaine Crooks (Swansea) Mathematical Biology Seminar Series 14:00 Hicks LT10 Nov 27 Tue Jack Shotton (Durham) Number Theory seminar 14:00 J11 TBA Nov 28 Wed Yanki Lekili (King's College London) Pure Maths Colloquium 14:00 J11 Dec 5 Wed Elisa Posthingel (Loughborough) Pure Maths Colloquium 14:00 J11 Dec 5 Wed Jake Shipley (SoMaS) Applied Mathematics Colloquium 14:00 Hicks, LT 11 Dec 10 Mon Rachel Norman (Stirling) Mathematical Biology Seminar Series 14:00 Hicks LT10 Dec 12 Wed Steffen Kionke (Karlsruhe Institute for Technology) Pure Maths Colloquium 14:00 J11 Dec 13 Thu Alice Pozzi (UCL) Number Theory seminar 14:00 J11 TBA