Seminars this semester
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 Gspectra  
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 Gspectra 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 onecentury 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 highresolution 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 largescale 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 nonrotating models and how that behavior changes as simulations are pushed toward more turbulent and/or more rotationallyconstrained 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 reinterpretation. 

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  CohenMacaulay 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 SwinnertonDyer  
Abstract: The conjecture of Birch and SwinnertonDyer 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 zeropressuregradient 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 NavierStokes 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 zeronet mass flow constraint of the actuation velocity. Results are also compared with uniform blowing using the same timeaverage velocity obtained from the nonlinear 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 Obimodules with Oalgebras, with applications.  
Abstract: If O is an operad (in a friendly category, e.g. the category of Smodules of stable homotopy theory), M is an Obimodule, A is an Oalgebra, then the circle product over O of M with A is again an Oalgebra. A useful derived version is the bar construction B(M,O,A). We survey many interesting constructions on Oalgebras that have this form. These include an augmentation ideal filtration of an augmented Oalgebra A, the topological AndreQuillen homology of A, the topological Hochschild homology of A, and the tensor product of A with a space. Right Omodules 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 2algebra, 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 2algebra, 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 2algebra, 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  Grainscale 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 grainsize evolution. The first model is formulated to capture the observed grainsize 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 LewisMaySteinberger and Shimakawa developed generalizations of the operadic approach and the Gammaspace 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  J11  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 halfcircle 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 LAgroupoid. 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  J11  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 Ktheory 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 Ktheory 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 Ktheory. 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 Lfunctions  
Abstract: In many ways Lfunctions 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 Lfunctions, in the spirit of the GanGrossPrasad 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 LAgroupoid. 

Mar 7  Tue  Haluk Sengun (Sheffield)  Number Theory Learning Seminar 
13:00  J11  Background. Part I.  
Mar 7  Tue  Neil Hansford (Sheffield)  Operator Ktheory 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  J11  Background. Part II.  
Abstract: Operators on Hilbert spaces. 

Mar 14  Tue  Jordan Williamson (Sheffield)  Operator Ktheory 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.


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 RempeGillen (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 RiotteLambert (Glasgow)  Mathematical Biology Seminar Series 
14:00  Alfred Denny Conference Room  Consequences of memorybased 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 LAgroupoid, and look at a specific example of an LAgroupoid 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  J11  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 Ktheory and Noncommutative Geometry Seminar 
14:00  J11  Ktheory 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  Metricindependence 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 jinvariant; their coarse moduli space is an affine line with the jinvariant as coordinate. Conversely, it is not difficult to construct an elliptic curve with a specified jinvariant. 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 quasiaffine 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 nonhyperelliptic 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 RempeGillen (Liverpool )  SoMaS Colloquium 
16:05  LT7  Metronomes and fireflies: Stability in the Arnold family  
Abstract: *Phaselocking* (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 onedimensional discretetime model of a periodically forced oscillator as the simplest context in which to study phaselocking phenomena. In this talk, I will describe a longstanding problem concerning the density of stable parameters within this family (arising from phaselocking 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 onedimensional discrete dynamics, including computer experiments of both the Arnold family and the wellknown 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  J11  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 Ktheory and Noncommutative Geometry Seminar 
14:00  J11  Ktheory of C*algebras. Part II.  
Mar 29  Wed  Ulrike Tillmann (University of Oxford)  Pure Maths Colloquium 
14:00  J11  Riemann's moduli spaces and operads  
Abstract: Riemann's moduli spaces are at the heart of much modern mathematics. In this lecture we will explore their properties as an operad. Operads were introduced in the 1970 in homotopy theory to study loop spaces. Infinite loop spaces are of particular interest as they give rise to generalised cohomology theories. In the 1990's operads had a renaissance with much interest stimulated from mathematical physics. In particular, Segal's axiomatic approach to conformal field theory defines an operad of Riemann surfaces. We will show that this is an example of a new generation of operads detecting infinite loop spaces. The talk will introduce the main concepts and is addressed to a general mathematical audience. 

Mar 30  Thu  TBA  Algebra / Algebraic Geometry seminar 
16:00  J11  
Mar 31  Fri  Norbert Gyenge (Sheffield)  SP2RC seminar 
13:00  F41  On Active Longitudes and their Relation to Loci of Coronal Mass Ejections  
Abstract: The spatial inhomogeneity of the distribution of coronal mass ejection (CME) loci in the solar atmosphere could provide a new tool to estimate the longitudinal position of the most probable CMEcapable active regions in the Sun. The anomaly in the longitudinal distribution of active regions themselves is often referred to as active longitude (AL). In order to reveal the connection between the AL and CME loci, here, we investigate the morphological properties of active regions. The first morphological property studied is the separateness parameter, which is suitable to characterise the probability of the locus of an energetic event, such as solar flare or CME. The second morphological property we focus on is the tilt angle of sunspot groups. Analysis of tilt angle of sunspot groups allows us to estimate the helicity of active regions. An increased helicity leads to a more complex builtup of the magnetic structure and also can be the cause of CME eruption. We found that the most complex active regions appear statisticlly significantly near to the AL and that the AL itself is associated with the most tilted active regions. Therefore, the number of CME loci is higher around the enhanced longitudinal activity. Further, the origin of the fast CMEs is also found to be associated with the AL belt. We concluded that the source of the most probably CMEcapable active regions is at the AL. Applying our method may allow us to predict the potential flare and CME sources several Carrington Rotation (CR) in advance, and, our further findings could provide new information for solar dynamo modelling. 

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  J11  Real story. Part II.  
Abstract: Representations of $SL(2,\mathbb{R})$. 

Apr 25  Tue  Sarah Browne (Sheffield)  Operator Ktheory 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 underrecording 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  J11  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 Ktheory and Noncommutative Geometry Seminar 
14:00  J11  Khomology  
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  J11  Adelic sotry. Part I.  
Abstract: Adeles, ideles. $GL(2)$ over the adeles, strong approximation. 

May 9  Tue  Sven Meinhardt (Sheffield)  Operator Ktheory 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 quasispectrum for graded Etheory  
Abstract: Graded Etheory 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 quasitopological space and explain why this notion is necessary in our case. We will define the notion of an orthogonal quasispectrum as an orthogonal spectrum for quasitopological spaces, and further give the quasitopological spaces to form the spectrum for graded Etheory. If time allows I will give the smash product structure. 

May 16  Tue  Ariel Weiss (Sheffield)  Number Theory Learning Seminar 
13:00  J11  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 Ktheory 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  Quasitopological 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  J11  Adelic story. Part III.  
Abstract: Tensor product theorem, odds and ends. 

May 23  Tue  Haluk Sengun (Sheffield)  Operator Ktheory and Noncommutative Geometry Seminar 
14:00  J11  The BaumConnes 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  