Seminars this semester


   Series:

 
Jan 18 Thu Thomas Wagner (Helsinki) Plasma Dynamics Group
16:00 Identifying and Tracking Coronal Flux Ropes
Google Meet
  Abstract:
To understand solar eruptions and the destabilization mechanism of the corresponding flux ropes, modelling the magnetic field in the solar corona in a time-dependent manner is commonly employed. However, identifying the field lines of solar flux ropes in simulation data is not trivial. We therefore developed a method for detecting and tracking flux ropes from modelling data. The extraction procedure uses a combination of some proxy map as input (for example the field line twist) and mathematical morphology algorithms, such as the morphological opening or the morphological gradient. The method is validated by applying it to time-dependent magnetofrictional model (TMFM) simulations of active regions AR11176 and AR12473. With full access to the flux rope field lines, we investigate the eruptivity and propagation of the flux ropes through the modelling domain. Finally, the methodology is also wrapped into a graphical user interface (GUI) to further simplify its application.
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Jan 22 Mon Dom Grainger
13:00
Hicks Seminar Room J11
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Jan 22 Mon Dom Grainger (Sheffield)
14:00
Hicks Seminar Room J11
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Jan 24 Wed Matteo Forconi (Rome) Cosmology, Relativity and Gravitation
15:00 JWST’s Revelations and the Super-LCDM’s Promise
Hicks Seminar Room J11
  Abstract:
The recent observations by the James Webb Space Telescope (JWST) of massive galaxies at high redshifts (z ∼ 10) significantly challenge the Lambda Cold Dark Matter (ΛCDM) cosmological model. These observations suggest a higher stellar mass density than previously predicted, and raise questions about galaxy formation and matter distribution in the early universe. To reconcile these findings with standard predictions, an investigation one can look into potential systematics. If systematic errors are ruled out, one might also wonder whether this new anomaly is somehow originated from the same underlying issue as the Hubble tension, suggesting the need for a beyond-ΛCDM phenomenological explanation. One potential avenue is exploring the Dark Energy Sector. Another challenge to the standard ΛCDM model arises from allowing non-Gaussian fluctuations. Using the super sample signal, it is possible to promote the standard ΛCDM model to a more comprehensive Super-ΛCDM model. This model allows to study non-Gaussianity traces using only the power spectrum. The implications of this model extend to the field of neutrino physics, indicating that the traditional constraints on neutrino masses might need revision.
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Jan 30 Tue Nirmal Kotal (Chennai Mathematical Institute )
16:00 On Knutson Ideals and Polyomino
Hicks Seminar Room J11
  Abstract:
Consider a polynomial f with a square-free leading term with respect to some monomial ordering. Consider the smallest set of ideals such that the principal ideal (f) is in the set; the colon ideal I:J is in the set for any ideal I in the set and any arbitrary ideal J; and if I and J are in the set, then the sum I+J and the intersection I∩J are in the set. Conca-Varbaro and Seccia extensively studied this class of ideals and called the members of the set as "Knutson ideals," associated with f, as they were first studied by A. Knutson. In this discussion, we will explore many algebraic features of these ideals, such as the Grobner basis, radicality, F-splitting, etc. A polyomino is a set of unit squares on the plane that is made by joining the squares side by side. Qureshi associated an ideal generated by 2-minors with polyomino. This presentation will explore the application of Knutson's methodology in the analysis of polyomino ideals. This is an ongoing joint project with Mitra Koley and Dharm Veer.
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Jan 31 Wed Sebastian Schuster (Sheffield) Cosmology, Relativity and Gravitation
15:00 What's Physical? A Space-Time Koan
Hicks Seminar Room J11
  Abstract:
Evaluating the physicality of a given space-time can prove difficult. Often, this is relegated to easy-to-check concepts: Absence of closed, time-like curves (vulgo: no time travel); validity of energy conditions (vulgo: mass/energy should be positive); geodesic completeness (vulgo: we shan't disappear); the related hole-freeness (vulgo: again, we shan't disappear); and more. The problem is that these are not necessarily mutually compatible with each other. Worse, as in the case of energy conditions, not all such concepts are either easy to justify or even fulfilled in known, physical situations. This talk will serve two purposes. The first is to make everyone queasy about the push-me-pull-you nature of physicality, as this allows us to critically examine which type of physicality may be more or less important in any given situation. Here, reverse-engineered metrics like warp drives and tractor beams will be in the spotlight. The second is to hone in on one particularly befuddling concept: Time travel. Fascinating as it is, in general relativity the space-time will either contain it or not. General relativity cannot explain why it might be there, or whether the confusion and contractions arising from it are due to the concept itself or from being in the wrong physical framework. Many arguments have to, at some point, wave their hands and allude to an unknown theory beyond it. To actually make this step beyond general relativity, I will present a very simple, quantum toy model of time travel with an emergent notion of time. While this first toy model will turn out to be not particularly illuminating, it still serves as a good starting point for more complicated toy models with richer structure.
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Feb 7 Wed Luca Marchetti (New Brunswick) Cosmology, Relativity and Gravitation
16:00 Scalar cosmological perturbations from quantum-gravitational entanglement
Hicks Seminar Room J11
  Abstract:
A major challenge at the interface between quantum gravity and cosmology is to understand how cosmological structures can emerge from physics at the Planck scale. In this talk, I will discuss the main challenges associated with the understanding of such an emergence process and provide a concrete example of how they can be addressed by extracting the physics of scalar and isotropic cosmological perturbations from full quantum gravity, as described by a causally complete Barrett-Crane group field theory model. From the perspective of the underlying quantum gravity theory, cosmological perturbations will be associated with (relational) nearest-neighbor two-body entanglement, providing crucial insights into the potentially purely quantum-gravitational nature of cosmological perturbations. I will also show that at low energies the emergent relational dynamics of these perturbations are perfectly consistent with those of general relativity, while at trans-Planckian scales quantum effects become important. Finally, I will comment on the implications of these quantum effects for the physics of the early universe and outline future research directions.
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Feb 8 Thu Balazs Asztalos SP2RC/ESPOS seminar
10:00 MHD Wave Propagation and Kelvin–Helmholtz Instability in Asymmetric Magnetic Slab Systems
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Feb 8 Thu PGR Lean Study Group
13:00
Hicks Seminar Room J11
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Feb 8 Thu Sarah Whitehouse (Sheffield) Topology Seminar
16:00 Homotopy theory of spectral sequences
Hicks Seminar Room J11
  Abstract:
For each r, maps which are quasi-isomorphisms on the r page provide a class of weak equivalences on the category of spectral sequences. The talk will cover homotopy theory associated with this setting. We introduce the category of extended spectral sequences and show that this is bicomplete by analysis of a certain presheaf category modelled on discs. We endow the category of extended spectral sequences with various model category structures. One of these has the property that spectral sequences is a homotopically full subcategory and so, by results of Meier, exhibits the category of spectral sequences as a fibrant object in the Barwick-Kan model structure on relative categories. We also note how the presheaf approach provides some insight into the décalage functor on spectral sequences. This is joint work with Muriel Livernet.
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Feb 9 Fri Matt Lennard & Jake Saunders (Sheffield)
16:00
Hicks Seminar Room J11
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Feb 12 Mon Dom Grainger (University of Sheffield)
15:00
Hicks Seminar Room J11
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Feb 13 Tue Luis Santiago Palacios (Bordeaux) Number Theory seminar
13:00 Geometry of the Bianchi eigenvariety at non-cuspidal points
Hicks Seminar Room J11 / Google Meet
  Abstract:
An important tool to study automorphic representations in the framework of the Langlands program, is to produce $p$-adic variation. Such variation is captured geometrically in the study of certain "moduli spaces" of p-adic automorphic forms, called eigenvarieties. In this talk, we first introduce Bianchi modular forms, that is, automorphic forms for $\mathrm{GL}_2$ over an imaginary quadratic field, and then discuss its contribution to the cohomology of the Bianchi threefold. After that, we present the Bianchi eigenvariety and state our result about its geometry at a special non-cuspidal point. This is a joint work in progress with Daniel Barrera (Universidad de Santiago de Chile).
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Feb 13 Tue Emmanouil Kalligeris (Sheffield) Statistics Seminar
15:00 A Twisted Markov Switching Mechanism for the Modelling of Incidence Rate Data
Hicks Seminar Room J11
  Abstract:
Various time series models have been used over the years to capture the dynamic behaviour of significant variables in various scientific fields such as epidemiology, seismology, meteorology, finance, etc. In this work, a conditional mean Markov regime switching model with covariates is proposed and studied for the analysis of incidence rate data. The components of the model are selected by both penalised likelihood techniques in conjunction with the Expectation Maximisation algorithm, with the aim of achieving a high level of robustness with respect to modelling the dynamic behaviour of epidemiological data. In addition to statistical inference, changepoint detection analysis is used to select the number of regimes, reducing the complexity associated with likelihood ratio tests. [Kalligeris EN, Karagrigoriou A, Parpoula C. (2023): On Stochastic Dynamic Modeling of Incidence Data. Int J Biostat, 10.1515/ijb-2021-0134]
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Feb 14 Wed Robin Stephenson (Sheffield) Probability seminar
16:00 Where do trees grow leaves?
Hicks Seminar Room J11
  Abstract:
We study a model of random binary trees grown ``by the leaves" in the style of Luczak and Winkler (2004). If $\tau_n$ is a uniform plane binary tree of size $n$, Luczak and Winkler, and later explicitly Caraceni and Stauffer, constructed a measure $\nu_{\tau_n}$ such that the tree obtained by adding a cherry on a leaf sampled according to $\nu_{\tau_n}$ is still uniformly distributed on the set of all plane binary trees with size $n+1$. It turns out that the measure $\nu_{\tau_n}$, which we call the leaf-growth measure, is noticeably different from the uniform measure on the leaves of the tree $\tau_n$. In fact we prove that as $n \to \infty$, with high probability it is almost entirely supported by a subset of only $n^{3 ( 2 - \sqrt{3})+o(1)} \approx n^{0.8038...}$ leaves. In the continuous setting, we construct the scaling limit of this measure, which is a probability measure on the Brownian Continuum Random Tree supported by a fractal set of dimension $ 6 (2 - \sqrt{3})$. We also compute the full (discrete) multifractal spectrum. This work is a first step towards understanding the diffusion limit of the discrete leaf-growth procedure.
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Feb 15 Thu Cora Uhlemann (Newcastle) Cosmology, Relativity and Gravitation
11:00 Making dark matter waves - the cosmic web and wavelike dark matter
Hicks Seminar Room J11
  Abstract:
Despite the astonishing success of cosmological probes in constraining the LCDM model, the dark matter mass remains one of the least constrained physical parameters. Wavelike dark matter is an intriguing alternative to standard cold dark matter with key particle physics motivations (like the QCD axion or ultralight axion-like particles) and distinct astrophysical signatures. With a simple dynamical model for the evolution of the dark matter wavefunction, I will demonstrate how to predict the formation of destructive and constructive wave interference leading to topological defects and granules dressing the cosmic web of large-scale structure. Our wave-based formalism is a versatile tool to describe the complex phase-space dynamics of cold dark matter in position space; and the fundamental description for wavelike dark matter such as ultralight particles, leading to exciting and varied probing mechanisms bridging cosmology and astroparticle physics.
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Feb 15 Thu PGR Lean Study Group
13:00
Hicks Seminar Room J11
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Feb 20 Tue Beth Romano (Kings College London) Number Theory seminar
13:00 Epipelagic representations in the local Langlands correspondence
Hicks Seminar Room J11 / Google Meet
  Abstract:
The local Langlands correspondence (LLC) is a kaleidoscope of conjectures relating local Galois theory, complex Lie theory, and representations of p-adic groups. The LLC is divided into two parts: first, there is the tame or depth-zero part, where much is known and proofs tend to be uniform for all residue characteristics p. Then there is the positive-depth (or wild) part of the correspondence, where there is much that still needs to be explored. I will talk about recent results that build our understanding of this wild part of the LLC via epipelagic representations and their Langlands parameters. I will not assume background knowledge of the LLC, but will give an introduction to these ideas via examples.
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Feb 21 Wed João Paulo M Pitelli (Campinas State) Cosmology, Relativity and Gravitation
15:00 Thermal effects on a global monopole with Robin boundary conditions
Hicks Seminar Room J11
  Abstract:
The quantum theory of a scalar field propagating on a spacetime with a naked singularity is not determined until we specify a boundary condition at the boundary. When this choice is not unique, any physical observable will depend on the particular choice of boundary condition. In this work we illustrate this explicit dependence by analyzing the transition rate of an Unruh-DeWitt detector coupled to a thermal state in the singular scenario of a global monopole. We show that the naked singularity manifests thermal effects with a non-trivial behavior with respect to the admissible boundary conditions. In particular, we show that the transition rate is finite at the singularity only for the Dirichlet boundary condition and that the divergence for the other possible (Robin) boundary conditions is consistent with the divergence of the thermal fluctuations.
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Feb 22 Thu Joseph Grant (UEA) Topology Seminar
16:00 Frobenius algebra objects in Temperley-Lieb categories at roots of unity
Hicks Seminar Room J11
  Abstract:
Frobenius algebras appear in many parts of maths and have nice properties. One can define algebra objects in any monoidal category, and there is a standard definition of when such an algebra object is Frobenius. But this definition is not satisfied by something which we'd like to think of as an algebra object in Temperley-Lieb categories at roots of unity. We will explore a more general definition of a Frobenius algebra object which covers this example, and will explore some of its properties. This is joint work with Mathew Pugh.
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Feb 22 Thu Renato Miotto (Unicamp, Brazil) Plasma Dynamics Group
16:00 Bridging the gap between numerical simulations and experiments through computer vision and deep learning
online / Google Meet
  Abstract:
Several physics and engineering problems require knowledge of physical properties to be completely characterized. However, such properties cannot always be easily obtained experimentally, which means that numerical simulations are often necessary to study the problem in question. In the present work, we propose to leverage data from numerical simulations to extract relevant information from experimental visualizations of the flow field using deep learning. We uniquely treat the image semantic segmentation as an image-to-image translation task that infers semantic labels of structures from the input images in a supervised way. The present methodology exploits the semantic proximity between images from the numerical and experimental domains to translate any properties of interest between them. Example applications are shown for a moving airfoil as well as for predicting forces on a sand dune. Extrapolation and interpolation for different flow regimes never seen by the neural network are discussed.
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Feb 26 Mon Carina Dunlop (Surrey) Mathematical Biology Seminar
13:00 What do cells and tissues feel? The integration of cell contractility, growth and adhesion in mechanosensing
Hicks Seminar Room J11
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Feb 27 Tue Alexandros Groutides (Warwick) Number Theory seminar
13:00 On integral structures in smooth $\mathrm{GL}_2$-representations and zeta integrals.
Hicks Seminar Room J11 / Google Meet
  Abstract:
We will discuss recent work on local integral structures in smooth ($\mathrm{GL}_2\times H$)-representations, where $H$ is an unramified maximal torus of $\mathrm{GL}_2$. Inspired by work of Loeffler-Skinner-Zerbes, we will introduce certain unramified Hecke modules containing lattices with deep integral properties. We'll see how this approach recovers a Gross-Prasad type multiplicity one result in this unramified setting and present an integral variant of it with applications to zeta integrals and automorphic modular forms. Finally, we will reformulate and answer a conjecture of Loeffler on integral unramified Hecke operators attached to the lattices mentioned above.
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Feb 27 Tue Prof. Robin Henderson (Newcastle University) Statistics Seminar
15:00 Event History and Topological Data Analysis
Hicks Seminar Room J11
  Abstract:
Topological data analysis has become popular in recent years, though mainly outside the statistical literature. In this talk we review some of the elements of topological data analysis and we show links to event history and survival analysis. We argue that exploiting topological data as event history can be useful in the analysis of data in the form of images. We propose a version of the well-known Nelson-Aalen cumulative hazard estimator for the comparison of topological features of random fields and for testing parametric assumptions. We suggest a Cox proportional hazards approach for the analysis of embedded metric trees. The Nelson-Aalen method is illustrated on globally distributed climate data and on neutral hydrogen distribution in the Milky Way. The Cox method is used to compare vascular patterns in fundus images of the eyes of healthy and diabetic retinopathy patients.
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Feb 28 Wed Ozgur Bayindir (Queen Mary University of London) Pure Maths Colloquium
14:00
Hicks Seminar Room J11
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Feb 29 Thu Jack Romo (Leeds) Topology Seminar
16:00
Hicks Seminar Room J11
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Mar 4 Mon Michael Clerx (Nottingham) Mathematical Biology Seminar
13:00 Estimating parameters for biological time-series models: lessons learned from a deep dive into ion channel modelling
Hicks Seminar Room J11
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Mar 5 Tue Lewis M Combes Number Theory seminar
13:00
Hicks Seminar Room J11 / Google Meet
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Mar 6 Wed Simon Willerton (Sheffield) Pure Maths Colloquium
14:00
Hicks Seminar Room J11
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Mar 6 Wed William Giare (Sheffield) Cosmology, Relativity and Gravitation
15:00
Hicks Seminar Room J11
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Mar 7 Thu Nadia Mazza (Lancaster) Topology Seminar
16:00 Endotrivial modules for finite groups of Lie type
Hicks Seminar Room J11
  Abstract:
Let G be a finite group and k a field of positive characteristic p diving the order of G. An endotrivial kG-module is a finitely generated kG-module which is "invertible" in some suitable sense. Since the late 70s, these modules have been intensely studied in modular representation theory. In this talk, we review the essential background on endotrivial modules, and present some results about endotrivial modules for finite groups of Lie type, obtained jointly with Carlson, Grodal and Nakano.
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Mar 8 Fri Stefano Gariazzo (IFT Madrid) Cosmology, Relativity and Gravitation
15:00
Hicks Seminar Room J11
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Mar 8 Fri Andrew Neate (Sheffield)
16:00
Hicks Seminar Room J11
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Mar 12 Tue Andrea Dotto (Cambridge) Number Theory seminar
13:00
Hicks Seminar Room J11 / Google Meet
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Mar 13 Wed Evgeny Shinder (Sheffield) Pure Maths Colloquium
14:00
Hicks Seminar Room J11
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Mar 13 Wed Eemeli Tomberg (Lancaster) Cosmology, Relativity and Gravitation
15:00
Hicks Seminar Room J11
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Mar 18 Mon Philip Pearce (UCL) Mathematical Biology Seminar
13:00 Some consequences of phenotypic heterogeneity in living active matter
Hicks Seminar Room J11
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Mar 20 Wed Emine Yildirim (University of Leeds) Pure Maths Colloquium
14:00
Hicks Seminar Room J11
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Mar 20 Wed Aindriú Conroy (Charles U Prague) Cosmology, Relativity and Gravitation
15:00
Hicks Seminar Room J11
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Mar 21 Thu Andy Baker (Glasgow) Topology Seminar
16:00
Hicks Seminar Room J11
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Apr 15 Mon Francesca Scarabel (Leeds) Mathematical Biology Seminar
13:00 Structured population models
Hicks Seminar Room J11
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Apr 17 Wed Tony Samuel (University of Birmingham) Pure Maths Colloquium
14:00
Hicks Seminar Room J11
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Apr 17 Wed Adrià Gómez Valent (Barcelona) Cosmology, Relativity and Gravitation
15:00
Hicks Seminar Room J11
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Apr 18 Thu Briony Eldridge (Southampton) Topology Seminar
16:00
Hicks Seminar Room J11
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Apr 24 Wed Catherine Meusburger (University of Erlangen) Pure Maths Colloquium
14:00
Hicks Seminar Room J11
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Apr 24 Wed Elsa Teixeira (Montpellier) Cosmology, Relativity and Gravitation
15:00
Hicks Seminar Room J11
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Apr 25 Thu Georg Struth (Sheffield) Topology Seminar
16:00
Hicks Seminar Room J11
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Apr 26 Fri Thomas Montandon (Montpellier) Cosmology, Relativity and Gravitation
15:00
Hicks Seminar Room J11
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Apr 30 Tue Bence Hevesi (Kings College London) Number Theory seminar
13:00
Hicks Seminar Room J11 / Google Meet
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May 1 Wed David Corfield (University of Kent) Pure Maths Colloquium
14:00
Hicks Seminar Room J11
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May 1 Wed Suddhasattwa Brahma (Edinburgh) Cosmology, Relativity and Gravitation
15:00
Hicks Seminar Room J11
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May 2 Thu Ehud Meir (Aberdeen) Topology Seminar
16:00
Hicks Seminar Room J11
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May 7 Tue Jay Taylor (Manchester) Number Theory seminar
13:00
Hicks Seminar Room J11 / Google Meet
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May 8 Wed Rohini Ramadas (University of Warwick) Pure Maths Colloquium
14:00
Hicks Seminar Room J11
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May 8 Wed Gabriele Barca (Rome/Sheffield) Cosmology, Relativity and Gravitation
15:00
Hicks Seminar Room J11
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May 20 Mon Juan Morales (Glasgow) Mathematical Biology Seminar
13:00
Hicks Seminar Room J11
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May 21 Tue Owen Patashnick (Kings College London) Number Theory seminar
13:00
Hicks Seminar Room J11 / Google Meet
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May 22 Wed Eleonora Di Valentino (Sheffield) Cosmology, Relativity and Gravitation
15:00
Hicks Seminar Room J11
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May 23 Thu Oliver House (Sheffield) Topology Seminar
16:00
Hicks Seminar Room J11
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