# Seminars this semester

Series:

 Jan 16 Mon John Greenlees (Sheffield) 11:00 J11 What we want from G spectra Jan 17 Tue Jordan Williamson (Sheffield) 14:00 J11 Orthogonal G-spectra Jan 17 Tue Sara Kalisnik (Brown) Topology seminar 16:00 J11 A short introduction to applied topology Abstract: In the last two decades applied topologists have developed numerous methods for ‘measuring’ and building combinatorial representations of the shape of the data. The most famous example of the former is persistent homology and of the latter, mapper. I will briefly talk about both of these methods and show several successful applications. Time permitting I will talk about my work on making persistent homology easier to combine with standard machine learning tools. Jan 19 Thu Jordan Williamson (Sheffield) 15:00 J11 Orthogonal G-spectra II Jan 20 Fri Dr Jiajia Liu (University of Science and Technology of China) SP2RC seminar 13:00 LT 11 Energy Rules of Solar Jets from Observational Perspectives Abstract: Solar jets are bulks of plasma materials ejected along elongated trajectories from the solar surface into the atmosphere of the Sun, often leaving the inner corona and determining the physical conditions far outwards in the interplanetary space. These impulsive and energetic ejecta are one of the most common dynamic phenomena occurring within the solar atmosphere. They are often accompanied by (nano-)flares, and some times by Coronal Mass Ejections (CMEs) and radio bursts, which could lead to significant changes of the space weather and terrestrial magnetic fields. After the nearly one-century efforts studying solar jets, we now have mature models for solar jets explaining the process of how magnetic reconnection triggers jets. However, due to the limits of the observational technology, many issues such as the detailed dynamics of, the energy transport during and the interaction with waves of solar jets are not well addressed before. In this talk, I will introduce part of my work during the past few years on the topic of "Energy Rules of Solar Jets from Observational Perspectives". Via high-resolution observations from the SDO and STEREO, I try to address the following questions of solar jets: (1) how the free magnetic energy is distributed between the thermal and kinetic energy during magnetic reconnection, (2) how the kinetic energy of solar jets is gained during and after the magnetic reconnection, and (3) how further release of the free magnetic reconnection proceeds after solar jets. Jan 24 Tue Luca Pol (Sheffield) 14:00 Complex cobordism and K theory with reality Jan 24 Tue Jonathan Sykes Uncertainty Quantification reading group 15:00 J11 Discussion of "Bayesian History Matching of Complex Infectious Disease Models Using Emulation: A Tutorial and a Case Study on HIV in Uganda", by Andrianikis et al. Jan 26 Thu Luca Pol (Sheffield) 15:00 Change of groups Jan 27 Fri Prof. B. Hindman (University of Colorado, Boulder) SP2RC seminar 13:00 LT 11 Solar convection in the rotationally constrained regime Abstract: Despite knowing that convection and rotation are indispensable components of the solar dynamo, we know vexingly little about how the influence of rotation manifests across the broad range of convective scales present in the Sun. We do know that the structure of deep meridional circulation, which may bear on the timing of the solar cycle, is sensitive to the degree of rotational constraint felt by its underlying convective motions. Similarly, the solar differential rotation, a vital source of large-scale shear in some dynamo models, results from convective motions that transport not just heat, but angular momentum. Rotation imbues convection with a sense of helicity, supplying a source of turbulent EMF to the dynamo, and it is only in regimes of strong rotational constraint that fully nonlinear models of stellar convection have evinced cyclic dynamo behavior. Current helioseismic measurements of the convective flows suggest that rotational influence is strong within the deep convection zone, but are inconsistent in how strong. Therefore, it is prudent to ask ourselves how rotation shapes the spectral distribution of convective power. I will present numerical results from a series of nonrotating and rotating convection simulations conducted in full spherical geometry. This presentation will focus on how convective spectra differ between the rotating and non-rotating models and how that behavior changes as simulations are pushed toward more turbulent and/or more rotationally-constrained regimes. I will conclude with a discussion of the implications that strong rotational constraint in the deep convection zone should have on the surface convective and how decades of surface observations may need re-interpretation. Jan 31 Tue Dimitar Kodjabachev (Sheffield) 14:00 Mackey functors Feb 2 Thu Dimitar Kodjabachev (Sheffield) 15:00 Fixed point functors Feb 3 Fri Dr. Rekha Jain (University of Sheffield) SP2RC seminar 13:00 LT 11 Feb 6 Mon Moty Katzman (Sheffield) Algebraic Geometry Learning Seminar 02:00 J11 Cohen-Macaulay modules Feb 6 Mon Torbjorn Lundh (Chalmers) Mathematical Biology Seminar Series 14:00 Hicks LT9 Four surgery problems "solved" by a "mathematical" approach Feb 7 Tue Jeremy Oakley (Sheffield) Uncertainty Quantification reading group 15:00 J11 Discussion of Wu, H., & Browne, M. W. (2015). Quantifying adventitious error in a covariance structure as a random effect. Psychometrika. Feb 7 Tue Jeff Giansiracusa (Swansea) Topology seminar 16:00 J11 Feb 8 Wed John Coates (University of Cambridge) Pure Maths Colloquium 14:00 J11 The conjecture of Birch and Swinnerton-Dyer Abstract: The conjecture of Birch and Swinnerton-Dyer is one of the principal open problems in number theory today. In my lecture, I shall give a brief account of the history of the conjecture, its precise formulation, and the partial results obtained so far in support of it. Feb 8 Wed George Papadakis (Imperial) Applied Mathematics Colloquium 14:00 Hicks, LT 10 Nonlinear optimal control of bypass transition in a boundary layer flow Abstract: We apply and assess a nonlinear optimal control strategy to suppress bypass transition in a zero-pressure-gradient boundary layer. To this end, a Lagrange variational formulation is employed that results in a set of adjoint equations. The optimal wall actuation (blowing and suction from a control slot) is found by solving iteratively the nonlinear Navier-Stokes and the adjoint equations in a forward/backward loop using DNS. The optimization is performed in a finite time horizon. Large values of optimization horizon result in instability of the adjoint equations. The control slot is located exactly in the region of transition. The results show that the control is able to significantly reduce the objective function, which is defined as the spatial and temporal integral of the quadratic deviation from the Blasius profile plus a term that quantifies the control cost. The physical mechanism with which the actuation interacts with the flow field is investigated and analysed in relation to the objective function employed. The spanwise averaged velocity is distorted by the control action, resulting in a significant reduction of the skin friction coefficient. We performed simulations with and without zero-net mass flow constraint of the actuation velocity. Results are also compared with uniform blowing using the same time-average velocity obtained from the non-linear optimal algorithm. Feb 10 Fri Dr Andrew Leonard (University of Sheffield) SP2RC seminar 13:00 F41 Feb 13 Mon Moty Katzman (Sheffield) Algebraic Geometry Learning Seminar 02:00 J11 Maximal Cohen Macaulay modules over hypersurfaces: matrix factorizations and periodic resolutions Feb 14 Tue Nick Kuhn (Virginia) Topology seminar 16:00 J11 The circle product of O-bimodules with O-algebras, with applications. Abstract: If O is an operad (in a friendly category, e.g. the category of S-modules of stable homotopy theory), M is an O-bimodule, A is an O-algebra, then the circle product over O of M with A is again an O-algebra. A useful derived version is the bar construction B(M,O,A). We survey many interesting constructions on O-algebras that have this form. These include an augmentation ideal filtration of an augmented O-algebra A, the topological Andre-Quillen homology of A, the topological Hochschild homology of A, and the tensor product of A with a space. Right O-modules come with canonical increasing filtrations, and this leads to filtrations of all of the above. In particular, I can show that a filtration on TAQ(A) defined recently by Behrens and Rezk agrees with one I defined about a decade ago, as was suspected. This is joint work with Luis Pereira. Feb 15 Wed Nicola Gambino (University of Leeds) Pure Maths Colloquium 14:00 J11 Commutative 2-algebra, operads, and analytic functors Abstract: Standard commutative algebra is based on commutative monoids, Abelian groups and commutative rings. In recent years, there has been some progress in developing an area that may be referred to as commutative 2-algebra, in which the familiar notions used in commutative algebra are replaced by their categorified counterparts (for example, commutative monoids are replaced by symmetric monoidal categories). The aim of this talk is to explain the analogy between standard commutative algebra and commutative 2-algebra, and to outline how this analogy suggests analogues of basic aspects of algebraic geometry. In particular, I will describe how some joint work with Andre’ Joyal on operads and analytic functors fits in this context. Feb 15 Wed Felix Ng (Department of Geography, Sheffiled) Applied Mathematics Colloquium 15:00 Hicks, LT 10 Grain-scale processes in the Earth's polar ice sheets Abstract: The spreading of the Antarctic and Greenland Ice Sheets is a slow viscous flow with nonlinear rheology. Besides temperature, grain sizes and crystal orientation within the polycrystalline ice are important factors behind the rheology. After giving this glaciological background, I will describe two mathematical models recently built to understand grain-size evolution. The first model is formulated to capture the observed grain-size profiles in ice cores. The second model tackles the fundamental process of normal grain growth (NGG), a coarsening process that occurs in metals as well as ice. Feb 20 Mon Nebojsa Pavic (Sheffield) Algebraic Geometry Learning Seminar 02:00 J11 Singularity category and MCM sheaves Feb 20 Mon Gary Mirams (Nottingham) Mathematical Biology Seminar Series 14:00 Alfred Denny Conference Room Feb 21 Tue Paul Gardner (Sheffield) Uncertainty Quantification reading group 15:00 J11 The use of Bayesian calibration in the prediction of damage in structures Abstract: This talk will include an overview of the field of structural health monitoring and damage identification, where the use of Bayesian calibrated models fit in and the aims of using this technique. It will conclude with challenges and future aims of using Bayesian calibrated subsystem models to make full system predictions of damage. Feb 21 Tue Angelica Osorno (Reed College) Topology seminar 16:00 J11 On equivariant infinite loop space machines Abstract: An equivariant infinite loop space machine is a functor that constructs genuine equivariant spectra out of simpler categorical or space level data. In the late 80's Lewis-May-Steinberger and Shimakawa developed generalizations of the operadic approach and the Gamma-space approach respectively. In this talk I will describe work in progress that aims to understand these machines conceptually, relate them to each other, and develop new machines that are more suitable for certain kinds of input. This work is joint with Anna Marie Bohmann, Bert Guillou, Peter May and Mona Merling. Feb 23 Thu Number Theory Learning Seminar 13:00 J-11 Organizational First Seminar Abstract: Organizational meeting: all interested parties are invited. Feb 24 Fri Alex Shukhobodskiy (University of Sheffield) SP2RC seminar 13:00 F41 Kink oscillations of expanding coronal loops Abstract: Kink waves and oscillations in a thin expanding magnetic tube in the presence of flow are studied. The tube consists of a core region and a thin transitional region at the tube boundary. In this region the plasma density monotonically decreases from its value in the core region to the value outside the tube. Both the plasma density and velocity of background flow vary along the tube and in time. Using the multiscale expansions the system of two equations describing the kink oscillations is derived. When there is no transitional layer the oscillations are described by the first of these two equations. This equation is used to study the effect of plasma density variation with time on kink oscillations of expanding tube with a sharp boundary. It is assumed that the characteristic time of the density variation is much larger than the characteristic time of kink oscillations. Then the WKB method is used to derive the expression for the aidiabatic invariant, which is the quantity that is coserved when the plasma density varies. The general theoretical results are applied to the kink oscillations of coronal magnetic loops. The expanding loops with the half-circle shape is considered and it is assumed that the plasma temperature inside a loop decays exponentially. The dependencies of the fundamental mode frequency, the ratio of frequencies of the first overtone and fundamental mode, and the oscillation amplitude on time are calculated numerically. Feb 27 Mon Evgeny Shinder (Sheffield) Algebraic Geometry Learning Seminar 02:00 J11 Knorrer periodicity Feb 27 Mon David Grimes (Oxford) Mathematical Biology Seminar Series 14:00 Alfred Denny Conference Room Feb 28 Tue Sam Morgan (Sheffield) Differential geometry seminar 11:00 J11 Double Lie groupoids and their double Lie algebroids, I Abstract: The series of talks will consist of a precise formulation of the double Lie algebroid of a double Lie groupoid. We will also discuss some of the examples arising in Poisson geometry. In the first talk we will consider the construction of the double Lie algebroid of an LA-groupoid. This will be a stepping stone in the general construction for a double Lie groupoid. Knowledge of the standard formation of the Lie algebroid of a Lie groupoid will not be assumed, and the notions of a Lie groupoid and a Lie algebroid will be recalled. Feb 28 Tue Haluk Sengun (Sheffield) Number Theory Learning Seminar 13:00 J-11 Automorphic Forms and Representation Theory: An Overview Abstract: We shall sketch the path that goes from modular forms to automorphic representations. Feb 28 Tue Operator K-theory and Noncommutative Geometry Seminar 14:00 J11 Organizational First Meeting Feb 28 Tue Gareth Williams (Open) Topology seminar 16:00 J11 Weighted projective spaces, equivariant K-theory and piecewise algebra Abstract: Weighted projective spaces are interesting through many lenses: for example, as natural generalisations of ordinary projective spaces, as toric varieties and as orbifolds. From the point of view of algebraic topology, it is natural to study their algebraic topological invariants – notably, their (equivariant) cohomology rings. Recent work has provided satisfying qualitative descriptions for these rings, in terms of piecewise algebra, for various cohomology theories. This talk will introduce weighted projective spaces as toric varieties and survey results on their (equivariant) cohomology rings, with particular focus on equivariant K-theory. It will conclude with recent results of Megumi Harada, Tara Holm, Nige Ray and the speaker, and indicate the flavour of current work of Tara Holm and the speaker. Mar 1 Wed Anne Taormina (University of Durham) Pure Maths Colloquium 15:00 J11 The riches of Mathieu Moonshine Abstract: In 2009, three Japanese theoretical particle physicists observed that the elliptic genus of a K3 surface, when expressed in terms of mock modular forms, exposes numbers that can be linked to the dimensions of finite dimensional representations of the sporadic group Mathieu 24. Since then, this intriguing connection has been studied from several points of view, other examples of the same type of phenomenon for other finite groups and mock modular forms have been discovered, and the research topic of New Moonshines’ has slowly caught the attention of researchers across fields. In this talk, I will describe the 2009 observation, now referred to as Mathieu Moonshine’, and explain the challenges faced by the theoretical physics community in understanding the origin and role of the huge Mathieu 24 finite symmetry in the context of strings compactified on K3 surfaces. In particular, I will discuss how this phenomenon is related to the geometry of K3 surfaces and introduce the concept of symmetry surfing. Mar 2 Thu Andrew Corbett (Bristol) Number Theory seminar 13:00 J11 Period integrals and special values of L-functions Abstract: In many ways L-functions have been seen to contain interesting arithmetic information; evaluating at special points can make this connection very explicit. In this talk we shall ask what information is contained in central values of certain automorphic L-functions, in the spirit of the Gan--Gross--Prasad conjectures, and report on recent progress. We also describe some surprising applications in analytic number theory regarding the `size' of a modular form. Mar 2 Thu Mark Walters (Queen Mary) Probability 14:00 Mar 7 Tue Sam Morgan (Sheffield) Differential geometry seminar 11:00 J11 Double Lie groupoids and their double Lie algebroids, II Abstract: In the second talk, we will briefly discuss some examples of Lie algebroids arising from Lie groupoids; this should tie in with the description of the Lie functor, given in the first seminar. We shall then continue the construction of a double Lie algebroid of an LA-groupoid. Mar 7 Tue Haluk Sengun (Sheffield) Number Theory Learning Seminar 13:00 J-11 Background. Part I. Mar 7 Tue Neil Hansford (Sheffield) Operator K-theory and Noncommutative Geometry Seminar 14:00 J11 An introduction to C*-algebras. Part I. Mar 7 Tue Jeremy Colman (Sheffield) Uncertainty Quantification reading group 15:00 J11 Discussion of "Modelling extremes using approximate Bayesian Computation", by R. Erhardt and S. A. Sisson Mar 7 Tue Will Mycroft Topology seminar 16:00 J11 Plethories of Cohomology Operations Abstract: Cohomology operations are a very useful property of a cohomology theory. The collection of cohomology operations has a very rich structure. Historically the dual notion, of homology cooperations, have been the main target of attention and a nice algebraic structure called a Hopf ring has been used to understand these. Unfortunately, the Hopf ring contains no structure that is dual to the notion of composition. Boardman, Wilson and Johnson attempt to rectify this situation by defining an enriched Hopf ring, although this structure is rather less pleasant. A 2009 theorem of Stacey and Whitehouse shows that the collection of cohomology operations has the structure of an algebraic object called a plethory and this expresses all the structure, including composition. In this talk I shall define the above concepts and illustrate some examples of plethories for known cohomology theories. Mar 14 Tue Jordan Williamson (Sheffield) Number Theory Learning Seminar 13:00 J-11 Background. Part II. Abstract: Operators on Hilbert spaces. Mar 14 Tue Jordan Williamson (Sheffield) Operator K-theory and Noncommutative Geometry Seminar 14:00 J11 An introduction to C*-algebras. Part II. Mar 14 Tue Dimitar Kodjabachev (Sheffield) Topology seminar 16:00 J11 Mar 14 Tue Dimitar Kodjabachev (Sheffield) Topology seminar 16:00 J11 Gorenstein duality for topological modular forms with level structure Abstract: Gorenstein duality is a homotopy theoretic framework that allows one to view a number of dualities in algebra, geometry and topology as examples of a single phenomenon. I will briefly introduce the framework and concentrate on illustrating it with examples coming from derived algebraic geometry, especially topological modular forms with level structure. Mar 15 Wed Andrei Jaikin (Autonomous University of Madrid) Pure Maths Colloquium 14:00 J11 On $l^2$-Betti numbers and their analogues in positive characteristic Abstract: Let $G$ be a group, $K$ a field and $A$ a $n$ by $m$ matrix over the group ring $K[G]$. Let $G=G_1>G_2>G_3\cdots$ be a chain of normal subgroups of $G$ of finite index with trivial intersection. The multiplication on the right side by $A$ induces linear maps $$\begin{array}{cccc} \phi_i: & K[G/G_i]^n & \to& K[G/G_i]^m\\ &&&\\ &(v_1,\ldots,v_n) &\mapsto& (v_1,\ldots,v_n)A.\end{array}$$ We are interested in properties of the sequence $\{\frac{\dim_K \ker \phi_i}{|G:G_i|}\}$. In particular, we would like to answer the following questions. Is there the limit $\lim_{i\to \infty}\frac{\dim_K \ker \phi_i}{|G:G_i|}$? If the limit exists, how does it depend on the chain $\{G_i\}$? What is the range of possible values for $\lim_{i\to \infty}\frac{\dim_K \ker \phi_i}{|G:G_i|}$ for a given group $G$? It turns out that the answers on these questions are known for many groups $G$ if $K$ is a number field, less known if $K$ is an arbitrary field of characteristic 0 and almost unknown if $K$ is a field of positive characteristic. In my talk I will give several motivations to consider these questions, describe the known results and present recent advances in the case where $K$ has characteristic 0. Mar 16 Thu Martin Dickson (King's College) Number Theory seminar 13:00 J11 Central $L$-values of twists of Siegel cusp forms of degree two Abstract: The $L$-functions attached to Siegel cusp forms of degree two are conjectured, and in some cases known, to satisfy algebraicity properties at central values. This algebraicity is particularly interesting for those cusp forms which are expected to correspond to rational abelian surfaces. I will discuss these conjectures, the periods for these $L$-values, and finally the formulation of exact formula for the central values of twists of the degree four $L$-function. This includes some joint work with A. Saha, A. Pitale, and R. Schmidt. Mar 16 Thu Lasse Rempe-Gillen (Liverpool) SoMaS Colloquium 16:00 LT7 Mar 16 Thu Lesley Longstone (Independent Police Complaints Commission) RSS Seminar Series 16:30 Hicks Room K14 Independent Police Complaints Commission: using statistics to improve public confidence Abstract: As part of the IPCC’s role in securing and maintaining public confidence in the complaints system, the IPCC uses learning from its work to influence changes in policing, ensure accountability and spreads best practice and high standards of service. We are responsible for producing national statistics on deaths in or following police contact and official statistics on public complaints made about the police. We also procure a nationally representative survey in England and Wales to measure public confidence in the police complaints system. The presentation provides an overview of the methodologies for these main statistical outputs and the challenges faced, including external interpretations and quality issues. It also considers uses of the data and making evidenced based decisions that allow us to drive continuous improvement. Mar 20 Mon Evgeny Shinder (Sheffield) Algebraic Geometry Learning Seminar 02:00 J11 BGG correspondence Mar 20 Mon Louise Riotte-Lambert (Glasgow) Mathematical Biology Seminar Series 14:00 Alfred Denny Conference Room Consequences of memory-based movement at the individual and population levels Mar 21 Tue Sam Morgan (Sheffield) Differential geometry seminar 11:00 J11 Double Lie groupoids and their double Lie algebroids, III Abstract: In the third talk we will complete the construction of a double Lie algebroid of an LA-groupoid, and look at a specific example of an LA-groupoid arising naturally from a Poisson Lie group. We will finish by discussing the general notion of a double Lie algebroid of a double Lie groupoid. Mar 21 Tue Prathan Jarupoonphol (Sheffield) Number Theory Learning Seminar 13:00 J-11 Background. Part III. Abstract: The Lie algebra of $SL(2,\mathbb{R})$, the universal enveloping algebra and its centre, action on smooth functions on $SL(2,\mathbb{R})$. Mar 21 Tue Paul Mitchener (Sheffield) Operator K-theory and Noncommutative Geometry Seminar 14:00 J11 K-theory of C*-algebras. Part I. Mar 21 Tue Richard Wilkinson (Sheffield) Uncertainty Quantification reading group 15:00 J11 Discussion of Wong, R. K. W., Storlie, C. B. and Lee, T. C. M. (2017), A frequentist approach to computer model calibration. J. R. Stat. Soc. B, 79: 635–648. Mar 22 Wed Martin Lotz (University of Manchester) Pure Maths Colloquium 14:00 J11 Geometric Probability and Phase Transitions: Applications of the Steiner and Weyl Tube Formula Abstract: The tube formulas of Steiner and Weyl express the measure of tubular neighbourhoods of geometric objects (convex sets and Riemannian manifolds, respectively) as polynomials with certain curvature invariants as coefficients. We introduce these formulas and discuss recent applications to fields such as geometric probability, concentration of measure, numerical analysis, and convex optimization. Based on work with D. Amelunxen, M.B. McCoy, J.A. Tropp, F. Cucker, P. Buergisser Mar 22 Wed Abraham Harte (Dublin City University) Applied Mathematics Colloquium 14:00 Hicks, LT 10 Metric-independence of electromagnetic fields Mar 23 Thu Jeroen Sijsling (Ulm) Number Theory seminar 13:00 J11 Reconstructing plane quartics from their invariants Abstract: Up to isomorphism, elliptic curves over $\mathbb{C}$ are classified by their j-invariant; their coarse moduli space is an affine line with the j-invariant as coordinate. Conversely, it is not difficult to construct an elliptic curve with a specified j-invariant. In higher genus the situation is quite a bit more complicated. The moduli space of smooth genus 2 curves, as determined by Igusa, is already no longer a quasi-affine space, although it is still birational. In this genus Clebsch and Mestre have developed methods to reconstruct curves from their invariants, which also apply to hyperelliptic curves of higher genus. These methods are however very specific to the hyperelliptic case and do not at all generalize. This talk describes joint work with Reynald Lercier and Christophe Ritzenthaler that describes how reconstruction is possible in the next simplest case: that of non-hyperelliptic curves in genus 3, or in other words smooth plane quartics in $\mathbb{P}^2$. Mar 23 Thu Jordan Williamson (Sheffield) Category Theory 14:00 LT10 The category of representations of a finite group Mar 23 Thu Weijun Xu (Warwick) Probability 14:00 Mar 23 Thu Lasse Rempe-Gillen (Liverpool ) SoMaS Colloquium 16:05 LT7 Metronomes and fireflies: Stability in the Arnold family Abstract: *Phase-locking* (or phase synchronisation) is a phenomenon, first discovered by Huygens in the 17th century, in which two interacting oscillators synchronise their frequencies. It occurs in a plethora of physical and biological systems, from simple interacting pendula (search for “metronomes synchronise” on youtube …) to the synchronised behaviour of fireflies. In the 1960s, Vladimir Arnold proposed a one-dimensional discrete-time model of a periodically forced oscillator as the simplest context in which to study phase-locking phenomena. In this talk, I will describe a long-standing problem concerning the density of stable parameters within this family (arising from phase-locking phenomena), which we were able to resolve in recent work with van Strien (Duke Math. J., 2015). The talk will begin with a gentle introduction to one-dimensional discrete dynamics, including computer experiments of both the Arnold family and the well-known logistic family from population dynamics. These experiments naturally lead to the formulation of the density problem. The talk will hence be accessible to a general mathematical audience, including postgraduate students. Time permitting, I will also discuss how these developments are connected to, and were made possible by, recent progress in the study of the dynamics of transcendental entire functions. Mar 24 Fri Eleanor Vickers (Sheffield) SP2RC seminar 13:00 F41 MHD surface waves in an inclined magnetic field Mar 27 Mon John Greenlees (Sheffield) Algebraic Geometry Learning Seminar 02:00 J11 Graded singularity category Mar 28 Tue David Spencer (Sheffield) Number Theory Learning Seminar 13:00 J-11 Real story. Part I. Abstract: Automorphic forms on $SL(2,\mathbb{R})$, automorphic form associated to a classical cusp form. Mar 28 Tue Paul Mitchener (Sheffield) Operator K-theory and Noncommutative Geometry Seminar 14:00 J11 K-theory of C*-algebras. Part II. Mar 29 Wed Ulrike Tillmann (University of Oxford) Pure Maths Colloquium 14:00 J11 Mar 30 Thu TBA Algebra / Algebraic Geometry seminar 16:00 J11 Apr 6 Thu TBA Algebra / Algebraic Geometry seminar 16:00 J11 Apr 24 Mon Sven Meinhardt (Sheffield) Algebraic Geometry Learning Seminar 02:00 J11 Matrix factorizations and Homological Mirror Symmetry Apr 24 Mon Mirela Domijan (Liverpool) Mathematical Biology Seminar Series 14:00 Alfred Denny Conference Room Apr 25 Tue Di Zhang (Sheffield) Number Theory Learning Seminar 13:00 J-11 Real story. Part II. Abstract: Representations of $SL(2,\mathbb{R})$. Apr 25 Tue Sarah Browne (Sheffield) Operator K-theory and Noncommutative Geometry Seminar 14:00 J11 Bott periodicicty. Apr 25 Tue Ana Lecuona Topology seminar 16:00 J11 Apr 26 Wed Vidit Nanda (Oxford) Pure Maths Colloquium 14:00 J11 tba Apr 26 Wed Cedric Beaume (Leeds) Applied Mathematics Colloquium 14:00 Hicks, LT 10 Apr 27 Thu Rachel Newton (Reading) Number Theory seminar 13:00 J11 TBA Apr 27 Thu Nick Bingham Probability 14:00 Apr 27 Thu TBA Algebra / Algebraic Geometry seminar 16:00 J11 Apr 27 Thu Jonty Rougier (Bristol) SoMaS Colloquium 16:00 LT7 Assessing the risk from large volcanic eruptions: Understanding the historical record Abstract: Volcanoes threaten many millions of people worldwide, disproportionately in developing countries. Fortunately, large explosive volcanic eruptions are rare, but this also makes it harder to assess the rate of eruptions for the purposes of risk assessment. This difficulty is compounded by an unreliable historical record, in which the probability of an eruption being recorded in a modern database is affected by the size of the eruption, and also the time and location. In joint work with volcanologists Steve Sparks and Kathy Cashman, I have been quantifying the recording probability regionally as a function of time, for large eruptions. From a mathematical point of view, this application has some intriguing features. Our results so far suggest that under-recording is much more severe than previously thought. We think that a similar situation exists for other major hazards, such as earthquakes. May 2 Tue Rudolf Chow (Sheffield) Number Theory Learning Seminar 13:00 J-11 Real sotry. Part III. Abstract: Spectral decomposition of $L^2(\Gamma \backslash SL(2,\mathbb{R}))$, the Duality Theorem. May 2 Tue David O'Sullivan (Sheffield Hallam ) Operator K-theory and Noncommutative Geometry Seminar 14:00 J11 K-homology May 4 Thu Sam Edis (Sheffield) Number Theory seminar 13:00 J11 TBA May 4 Thu Ziyu Zhang (Hannover) Algebra / Algebraic Geometry seminar 16:00 J11 TBA May 8 Mon Steve Webb (Liverpool John Moores) Mathematical Biology Seminar Series 14:00 Alfred Denny Conference Room May 9 Tue Dimitar Kodjabachev (Sheffield) Number Theory Learning Seminar 13:00 J-11 Adelic sotry. Part I. Abstract: Adeles, ideles. $GL(2)$ over the adeles, strong approximation. May 9 Tue Sven Meinhardt (Sheffield) Operator K-theory and Noncommutative Geometry Seminar 14:00 J11 Group actions, group C*-algebra, crossed product algebras. Part I. May 10 Wed Barbara Bolognese (Sheffield) Pure Maths Colloquium 14:00 J11 tba May 11 Thu Herbert Gangl (Durham) Number Theory seminar 13:00 J11 TBA May 11 Thu Alistair Craw (Bath) Algebra / Algebraic Geometry seminar 16:00 J11 May 16 Tue Sarah Browne (Sheffield) Topology seminar 00:00 J11 An orthogonal quasi-spectrum for graded E-theory Abstract: Graded E-theory is a bivariant functor from the category where objects are graded C*-algebras and arrows are graded *-homomorphisms to the category where objects are abelian groups and arrows are group homomorphisms. It is bivariant in the sense that it is a cohomology theory in its first variable and a homology theory in its second variable. In this talk I'll give a description of a quasi-topological space and explain why this notion is necessary in our case. We will define the notion of an orthogonal quasi-spectrum as an orthogonal spectrum for quasi-topological spaces, and further give the quasi-topological spaces to form the spectrum for graded E-theory. If time allows I will give the smash product structure. May 16 Tue Ariel Weiss (Sheffield) Number Theory Learning Seminar 13:00 J-11 Adelic story. Part II. Abstract: Automorphic forms on $GL(2)$ over the adeles, the automorphic representation associated to a classical cuspidal modular form. May 16 Tue Haluk Sengun (Sheffield) Operator K-theory and Noncommutative Geometry Seminar 14:00 J11 Group actions, group C*-algebra, crossed product algebras. Part II. May 16 Tue Sarah Browne (Sheffield) Topology seminar 16:00 J11 Quasi-topological assembly for K theory May 17 Wed Kasia Rejzner (University of York) Pure Maths Colloquium 14:00 J11 May 18 Thu Sean Ledger (Bristol) Probability 14:00 Hicks LT E May 18 Thu Ciaran Meachan (Glasgow) Algebra / Algebraic Geometry seminar 16:00 J11 May 23 Tue Number Theory Learning Seminar 13:00 J-11 Adelic story. Part III. Abstract: Tensor product theorem, odds and ends. May 23 Tue Haluk Sengun (Sheffield) Operator K-theory and Noncommutative Geometry Seminar 14:00 J11 The Baum-Connes conjecture. May 24 Wed Alvar Daza (Universidad Rey Juan Carlos) Applied Mathematics Colloquium 14:00 Hicks, LT 10 Topological Properties of Escape Basins in Open Systems May 25 Thu TBA Algebra / Algebraic Geometry seminar 16:00 J11 Jun 1 Thu TBA Algebra / Algebraic Geometry seminar 16:00 J11 Jun 8 Thu TBA Algebra / Algebraic Geometry seminar 16:00 J11