Seminars this semester

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.

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.

Jan 31

Wed

Sebastian Schuster (Sheffield)

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.

Feb 7

Wed

Luca Marchetti (New Brunswick)

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.

Feb 8

Thu

Balazs Asztalos

10:00

MHD Wave Propagation and Kelvin–Helmholtz Instability in Asymmetric Magnetic Slab Systems

Feb 8

Thu

PGR Lean Study Group

13:00

Hicks Seminar Room J11

Feb 8

Thu

Sarah Whitehouse (Sheffield)

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.

Feb 9

Fri

Matt Lennard & Jake Saunders (Sheffield)

16:00

Hicks Seminar Room J11

Feb 12

Mon

Dom Grainger (University of Sheffield)

15:00

Hicks Seminar Room J11

Feb 13

Tue

Luis Santiago Palacios (Bordeaux)

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).

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]

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.

Feb 15

Thu

Cora Uhlemann (Newcastle)

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.

Feb 15

Thu

PGR Lean Study Group

13:00

Hicks Seminar Room J11

Feb 20

Tue

Beth Romano (Kings College London)

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.

Feb 21

Wed

João Paulo M Pitelli (Campinas State)

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.

Feb 22

Thu

Joseph Grant

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.

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.

Feb 26

Mon

Carina Dunlop (Surrey)

13:00

What do cells and tissues feel? The integration of cell contractility, growth and adhesion in mechanosensing

Hicks Seminar Room J11

Feb 27

Tue

Alexandros Groutides (Warwick)

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.

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.

Feb 28

Wed

Ozgur Bayindir (Queen Mary University of London)

14:00

Algebraic K-theory and chromatic redshift

Hicks Seminar Room J11

Abstract:
I will begin with an introduction to algebraic K-theory, ring spectra and the chromatic redshift conjecture. After this, I will talk about our new proof of the redshift conjecture for Lubin-Tate spectra and our algebraic K-theory computations. This work is partially joint with Christian Ausoni and Tasos Moulinos.

Feb 29

Thu

Jack Romo (Leeds)

16:00

$(\infty, 2)$-Categories and their Homotopy Bicategories

Hicks Seminar Room J11

Abstract:
Across the multitude of definitions for a higher category, a dividing line can be found between two major camps of model. On one side lives the ‘algebraic’ models where composition operations between morphisms are given, like Bénabou’s bicategories, tricategories following Gurski and the models of n-category of Batanin and Leinster, Trimble and Penon. On the other end, one finds the ‘non-algebraic’ models, where the space of possible composites is only guaranteed to be contractible. These include the models of Tamsamani and Paoli, along with quasicategories, Segal n-categories, complete n-fold Segal spaces and more. The bridges between these models remain somewhat mysterious. Progress has been made in certain instances, as seen in the work of Tamsamani, Leinster, Lack and Paoli, Cottrell, Campbell, Nikolaus and others. Nonetheless, the correspondence remains incomplete; indeed, for instance, there is no fully verified means in the literature to take an `algebraic’ homotopy n-category of any known model of $(\infty, n)$-category for general n. In this talk, I will present my contributions to the problem of taking algebraic homotopy bicategories of non-algebraic $(\infty, 2)$-categories. This talk also serves as an introduction to the model of $(\infty, 2)$-category I will be using, namely complete 2-fold Segal spaces. If time permits, I will discuss how to compute the fundamental bigroupoid of a topological space with this construction.

Mar 4

Mon

Michael Clerx (Nottingham)

13:00

Estimating parameters for biological time-series models: lessons learned from a deep dive into ion channel modelling

Hicks Seminar Room J11

Mar 4

Mon

Lea Bottini

14:00

Gapped phases and phase transitions from the SymTFT

Hicks Seminar Room J11

Abstract:
In this talk, I will introduce the concept of Symmetry Topological Field Theory (SymTFT); this is a (d+1)-dimensional topological theory associated to a d-dimensional theory T, which neatly encodes its symmetry properties and has emerged as a key tool to study generalized symmetries. In particular, I will show how the SymTFT can be used to determine gapped infra-red phases of 2d theories that have a symmetry S described in general by a fusion category. This approach gives concrete computational tools to extract information on the gapped phase, such as the symmetry breaking pattern, the number of vacua, and the action of the symmetry on such vacua. Moreover, I will introduce a generalization of the usual SymTFT framework that allows us to characterize phase transitions between such gapped phases. The SymTFT also manifestly encodes the order parameters for the phases, thus providing a generalized version of the Landau paradigm for symmetries that go beyond the standard group-like case.

Mar 4

Mon

Franco Rota

15:00

Non-degeneracy invariants of Enriques surfaces

Hicks Seminar Room J11

Abstract:
Every Enriques surface Y has an elliptic pencil, and every elliptic pencil on Y has two multiple fibers, whose reduced support is called a half-fiber. The non-degeneracy invariant of an Enriques surface is defined to be the maximum number of half-fibers meeting each other at exactly one point. This invariants influences the projective geometry of Y, as well as the structure of its derived category. In collaboration with R. Moschetti and L. Schaffler, we study techniques to compute non-degeneracy. These mix computer algebra and classical geometric methods. I'll illustrate our results in a few examples and I'll outline future directions.

Mar 5

Tue

Lewis M Combes

13:00

Period polynomials of level 1 Bianchi modular forms

Hicks Seminar Room J11 / Google Meet

Abstract:
The period polynomial of a classical modular form encodes important arithmetic information about the form itself, being made out of critical L-values and connecting to congruences via Haberland's formula. In this talk, we report on work to generalise these connections to the setting of Bianchi modular forms---those over an imaginary quadratic field. We demonstrate explicit congruences between various types of Bianchi modular form, and show how to detect them using a pairing on period polynomials.

Mar 6

Wed

Simon Willerton (Sheffield)

14:00

Instantaneous dimension of metric spaces via spread and magnitude

Hicks Seminar Room J11

Abstract:
Some spaces seem to have different dimensions at different scales. A long thin strip might appear one-dimensional at a distance, then two-dimensional when zoomed in on, but when zoomed in on even closer it is seen to be made of a finite array of points, so at that scale it seems zero-dimensional. I will present a way of quantifying this phenomenon using a couple of measures of the size of metric spaces, namely magnitude and spread. I will show lots of examples for finite metric spaces.

Mar 6

Wed

William Giare (Sheffield)

15:00

Do we need to rethink inflation?

Hicks Seminar Room J11

Abstract:
I will discuss some arguments that have led me to question whether we need to reassess our understanding of cosmic inflation. Large-scale CMB temperature and polarization measurements from the Planck satellite and the BICEP/Keck collaboration have established stringent constraints on the amplitude of primordial gravitational waves (r < 0.036) and the spectral index of scalar modes (ns = 0.9649 ± 0.0044). In contrast, small-scale CMB data from the Atacama Cosmology Telescope yield divergent predictions, pointing towards a scale-invariant spectrum (ns = 1.008 ± 0.015). This leads to an overall disagreement regarding the inflationary potential as inferred by CMB experiments probing different angular scales in the sky. The well-known Hubble tension further compounds the challenge. Solutions involving new physics at early times may reshape the predictions for inflation based on large-scale measurements to align with trends observed in small-scale data. As a result, with inflation, we find ourselves between the known and the unknown.

Mar 7

Thu

Ryan Campbell (Queen's University Belfast, United Kingdo)

10:00

DKIST's view of quiet photospheric magnetism and application of neural networks to the characterisation of Stokes profiles

Abstract:
A new era of solar physics commences with observations of the quiet Sun using the 4-metre Daniel K. Inouye Solar Telescope/Visible Spectropolarimeter (DKIST/ViSP). We present full-Stokes observations taken during DKIST’s cycle 1, in the Fe I 630.1/630.2 nm lines, allowing us to examine small-scale magnetism in the photosphere. We use the Stokes Inversion based on Response functions (SIR) code to invert the Fe I line pair. We reveal the existence of a serpentine magnetic element for the first time. A statistical analysis is undertaken, comparing inversions of DKIST data with Hinode data. A novel machine learning technique is used to characterise and contrast the shapes of circular polarisation signals found in the ground-based and space-based data, and synthetic observations produced from MANCHA simulations are used to aid our understanding of the differences between datasets.

Mar 7

Thu

Nadia Mazza (Lancaster)

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.

Mar 8

Fri

Fabrizio del Monte (Sheffield)

11:00

Mar 8

Fri

Stefano Gariazzo (IFT Madrid)

15:00

Relic neutrinos: decoupling and direct detection perspectives

Hicks Seminar Room J11

Abstract:
A background radiation of relic neutrinos, originated during the early phases of the Universe expansion, is predicted by the standard cosmological model, but has never been confirmed by a direct measurement. In this seminar, I will review some of the theoretical and phenomenological aspects of relic neutrino decoupling, present indirect evidence of their existence and discuss proposed techniques and ongoing experimental efforts for attempting the first direct detection of the neutrino background.

Mar 8

Fri

Andrew Neate (Sheffield)

16:00

Hicks Seminar Room J11

Mar 11

Mon

Alex Fletcher (Sheffield)

13:00

Hicks J11

Mar 12

Tue

Andrea Dotto (Cambridge)

13:00

Some consequences of mod p multiplicity one for Shimura curves

Hicks Seminar Room J11 / Google Meet

Abstract:
The multiplicity of Hecke eigenspaces in the mod p cohomology of Shimura curves is a classical invariant, which has been computed in significant generality when the group is split at p. This talk will focus on the complementary case of nonsplit quaternion algebras, and will describe a new multiplicity one result, as well as some of its consequences regarding the structure of completed cohomology. I will also discuss applications towards the categorical mod p Langlands correspondence for the nonsplit inner form of GL_2(Q_p). Part of the talk will comprise a joint work in progress with Bao Le Hung.

Mar 13

Wed

Evgeny Shinder (Sheffield)

14:00

Gromov's cancellation question in birational algebraic geometry

Hicks Seminar Room J11

Abstract:
I explain some cancellation and non-cancellation phenomena in algebraic geometry and relate them to the structure of the Grothendieck ring of varieties and to the groups of birational self-maps of algebraic varieties, in particular the Cremona groups.

Mar 13

Wed

Eemeli Tomberg (Lancaster)

15:00

Primordial black holes and stochastic inflation

Hicks Seminar Room J11

Abstract:
Quantum fluctuations from cosmic inflation give rise to the macroscopic structures of the universe. The strongest fluctuations collapse into primordial black holes, a dark matter candidate and a possible source of gravitational waves. Stochastic inflation is a tool to compute the fluctuation statistics non-perturbatively, needed for accurate black hole predictions. I discuss recent progress in these computations, their numerical implementation and analytical approximations, and the implications for black hole abundance in single-field models of inflation.

Mar 14

Thu

Giannis Dakanalis (National Observatory of Athens)

Plasma Dynamics Group

16:00

Swirling motions in the lower solar atmosphere: detection, statistics and profile analysis from multi-wavelength observations

LT6 (Hicks Building)

Abstract:
Ubiquitous vortical motions in the solar atmosphere have been recently revealed by high resolution observations from both space-borne and ground-based observatories in quiet, as well as, in active regions. In chromospheric observations obtained in spectral lines, such as the Halpha and Ca II IR, they manifest themselves as swirling dark spiral- and circular-shaped patches known as “chromospheric swirls”. Their suggested contribution to the channeling of energy, mass and momentum from the sub-photospheric to the higher layers of the solar atmosphere places them amongst potential candidates for atmospheric heating. In this context, their detection and statistical information concerning their population and several significant physical parameters and properties are of vital importance. To overcome the drawbacks of the detection methods based on visual inspection or on the Local Correlation Tracking (LCT) techniques, we have developed a novel automated detection method, which is purely based on their morphological characteristics. We will be presenting a brief description of the algorithm and the results from its application on high- resolution observations obtained with the CRisp Imaging SpectroPolarimeter (CRISP) of the Swedish 1-m Solar Telescope (SST) in three chromospheric spectral lines, namely, the Halpha, Ca II IR and Ca II K lines. The results include several statistical parameters such as their number, spatial distribution and temporal evolution, as well as significant physical parameters, such as radii and lifetimes. Specifically, for the estimation of the mean lifetime, apart from the usual approaches, the statistical method of survival analysis was implemented. This approach, which estimates more accurately the mean lifetime of a population, although common in several other scientific fields, is scarcely used in solar physics/astrophysics. We will finally be focusing on co-spatially detected swirling structures in all three chromospheric lines and the profile analysis performed to derive significant physical parameters, such as line-of-sight velocities, FWHM and equivalent widths.

Mar 15

Fri

Noemi Zsamberger (Sheffield)

13:00

Non-parallel wave propagation in an asymmetric magnetic slab

Google meet link: https://meet.google.com/ciq-zovu-rzm

Abstract:
Interactions between the highly dynamic atmosphere of our Sun and the magnetic fields permeating its atmosphere give rise to a wide variety of magnetohydrodynamic (MHD) wave phenomena. Combining observations of MHD waves with an applied mathematical description of the waveguides has allowed researchers to determine elusive physical quantities of the solar atmosphere using the methods of solar magneto-seismolgy. The ‘classical’ models utilised in this discipline describe straight, symmetrical MHD waveguides (slabs or flux tubes). A recent direction of research has focused on wave propagation in asymmetric slab waveguides, where the direction of propagation was strictly parallel to the magnetic field lines within the slab. Here, some further results are presented in the case when a magnetic slab is embedded in a non-magnetic, asymmetric environment, and the direction of propagation is allowed to deviate from the internal magnetic field lines of the slab. We describe this non-parallel wave propagation in various analytical approximations relevant to solar atmospheric waveguides (thin and wide slabs, low-beta plasmas) and present numerical solutions to the full dispersion relation to expand on our findings.

Mar 18

Mon

Philip Pearce (UCL)

13:00

Some consequences of phenotypic heterogeneity in living active matter

Hicks Seminar Room J11

Mar 18

Mon

Qaasim Shafi (Birmingham)

14:00

Refined curve counts on surfaces with descendants

Hicks Seminar Room J11

Abstract:
An old theorem of Mikhalkin says that the number of rational plane curves of degree d through 3d-1 points is equal to a count of tropical curves, combinatorial objects which are more amenable to computations. One can try to generalise this result in two directions, either by allowing for higher genus curves or allowing for different conditions than solely passing through points. I’ll discuss a generalisation which does both, using intersection theory on the moduli space of curves and integrable hierarchies, as well as ongoing work connecting this thread to quantum scattering diagrams coming from log Calabi-Yau surfaces. This is joint work with Patrick Kennedy-Hunt and Ajith Urundolil Kumaran.

Mar 19

Tue

Yoon Jae Nho

10:00

Spectral networks and Floer theory

Hicks Seminar Room J11

Abstract:
In this talk, I will give a brief introduction to the theory of spectral networks on a marked Riemann surface. I will describe how the GMN non-abelianization map can be understood in terms of Lagrangian Floer theory of the spectral curve in the cotangent bundle of the Riemann surface, for the quadratic differentials case. If time permits, I will describe one way to generalize this to the higher rank situation.

Mar 19

Tue

Jake Saunders (Booking room for online talk at Southampton PGR Seminar)

12:00

Hicks Seminar Room J11

Mar 20

Wed

Emine Yildirim (University of Leeds)

14:00

Why the Return to Pictures in Algebra?

Hicks Seminar Room J11

Abstract:
In ancient Greece, geometry was about points, lines, circles, and communicated through pictures. The 17th Century marked a transformative shift, connecting geometry with algebra, and lead to working with equations over visual representations. Algebraic geometry emerged as a magical blend of geometric intuition and algebraic methods. Commutative algebra, mainly the study of polynomial rings and their ideals, dominated the field for an extensive period. Then with the emergence of noncommutative algebras, such as matrix algebras, our unstoppable geometric intuition hit an immovable wall. The solution? A return to pictures as representations. In this expository talk, I will introduce a visual perspective on algebras, exploring path algebras and their captivating connections to different fields.

Mar 20

Wed

Aindriú Conroy (Charles U Prague)

15:00

Unruh-DeWitt Particle Detectors in Bouncing Cosmologies

Hicks Seminar Room J11

Abstract:
There is no well-defined notion of a particle in quantum field theory in curved spacetime due to the lack of global symmetries. The standard procedure in quantum field theory is to treat fields rather than particles as the fundamental object of interest. Nevertheless, in a seminal 1976 paper by W. G. Unruh, an operational meaning was given to the particle concept by examining the absorption and emission of field quanta by a two-level atom. This is the so-called Unruh-DeWitt detector and, in this operational sense, we say a particle is what a particle detector detects! In this talk, we begin by formulating an analytic model of a non-singular bouncing cosmology, the bounce phase of which receives a correction inspired by loop quantum cosmology. We then study the semi-classical particle production associated with spacetime within the Unruh-DeWitt particle detector framework, analysing the rate of particle detection with the aim of (a) understanding quantum effects at early times; (b) identify relics of pre-bounce physics; and (c) highlighting signatures of non-singular theories.

Mar 21

Thu

Július Koza (Astronomical Institute, Slovak Academy of Sciences, Slovakia)

10:00

Data-driven model of temporal evolution of the solar Mg II h and k profiles over the solar cycle

Abstract:
The solar radiation in the cores of the Mg II h & k spectral lines strongly correlates with solar magnetic activity and global variations of magnetic fields with the solar cycle. This work provides a data-driven model of temporal evolution of the solar full-disk Mg II h & k profiles over the solar cycle. Based on selected 76 IRIS near-UV full-Sun mosaics covering almost the full solar cycle 24, we find the parameters of double-Gaussian fits of the disk-averaged Mg II h & k profiles and a model of their temporal evolution parameterized by the Bremen composite Mg II index. The Markov Chain Monte Carlo algorithm implemented in the IDL toolkit SoBAT is used in modeling and predicting temporal evolution of the Mg II h & k peak-to-center intensity ratio and the Bremen Mg II index. The relevant full-disk Mg II h & k calibrated profiles with uncertainties and spectral irradiances are provided as an online machine-readable table. To facilitate utilization of the model corresponding routines, written in IDL, are made publicly available at GitHub.
Co-authors: Stanislav Gunár (The Czech Academy of Sciences, Czech Republic), Pavol Schwartz (Slovak Academy of Sciences, Slovakia), Petr Heinzel (The Czech Academy of Sciences, Czech Republic; University of Wrocław, Poland), Wenjuan Liu (The Czech Academy of Sciences, Czech Republic)
Web announcement: https://espos.stream/2024/03/21/Koza/
Zoom link: https://zoom.us/j/165498165
(Meeting ID: 165 498 165)

Mar 21

Thu

Andy Baker (Glasgow)

16:00

Endotrivial modules for the quaternion group and iterated Jokers in chromatic homotopy theory

Hicks Seminar Room J11

Abstract:
The Joker is a famous very singular example of an endotrivial module over the 8-dimension subHopf algebra of the mod 2 Steenrod algebra generated by $\operatorname{Sq}^1$ and $\operatorname{Sq}^2$. It is known that this can be realised as the cohomology of two distinct Spanier-Whitehead dual spectra. Similarly, the double and iterated double are also realisable, but then the process stops.

Apr 4

Thu

Daniel Nóbrega-Siverio (Instituto de Astrofísica de Canarias —IAC, Spain)

10:00

Deciphering solar coronal heating: Energizing small-scale loops through surface convection

Abstract:
The solar atmosphere is filled with clusters of hot small-scale loops commonly known as Coronal Bright Points (CBPs). These ubiquitous structures stand out in the Sun by their strong X-ray and/or extreme-ultraviolet (EUV) emission for hours to days, which makes them a crucial piece when solving the solar coronal heating puzzle. Here we present a novel 3D numerical model using the Bifrost code that explains the sustained CBP heating for several hours. We find that stochastic photospheric convective motions alone significantly stress the CBP magnetic field topology, leading to important Joule and viscous heating concentrated around the CBP’s inner spine at a few megameters above the solar surface. We validate our model by comparing simultaneous CBP observations from SDO and SST with observable diagnostics calculated from the numerical results for EUV wavelengths as well as for the Halpha line using the Multi3D synthesis code.
Co-authors: Fernando Moreno-Insertis, Klaus Galsgaard, Kilian Krikova, Luc Rouppe van der Voort, Reetika Joshi, and Maria Madjarska
Web announcement: https://espos.stream/2024/04/04/Nobrega-Siverio/
Zoom link: https://zoom.us/j/165498165
(Meeting ID: 165 498 165)

Apr 15

Mon

Francesca Scarabel (Leeds)

13:00

Structured population models

Hicks Seminar Room J11

Apr 15

Mon

Johannes Walcher (Heidelberg)

14:00

Exponential networks for linear partitions

Hicks Seminar Room J11

Abstract:
Previous work has given proof and evidence that BPS states in local Calabi-Yau 3-folds can be described and counted by exponential networks on the punctured plane, with the help of a suitable non-abelianization map to the mirror curve. This provides an appealing elementary depiction of moduli of special Lagrangian submanifolds, but so far only a handful of examples have been successfully worked out in detail. In this talk, I will present an explicit correspondence between torus fixed points of the Hilbert scheme of points on C^2\subset C^3 and anomaly free exponential networks attached to the quadratically framed pair of pants. This description realizes an interesting, and seemingly novel, "age decomposition'' of linear partitions. We also provide further details about the networks' perspective on the full D-brane moduli space.(Joint work with Sibasish Banerjee, Mauricion Romo, Raphael Senghaas)

Apr 16

Tue

Dominic Grainger and Dr Ben Wigley (Sheffield)

Statistics Seminar

15:00

Dominic: The Efficient Modelling of Individual Animal Movement in Continuous Time; Ben: Stressing over shape: A Procrustean investigation of dental fluctuating asymmetry.

Hicks Seminar Room J11

Apr 17

Wed

Tony Samuel (University of Birmingham)

14:00

Complexity and geometry of aperiodic systems

Hicks Seminar Room J11

Abstract:

Aperiodic sequences and sequence spaces form prototypical mathematical models of quasicrystals. The most quintessential examples include subshifts of Sturmian words and substitutions, which are ubiquitous objects in ergodic theory and aperiodic order. Two of the most striking features these shift spaces have, are that they have zero topological entropy and are uniquely ergodic. Random substitutions are a generalisation of deterministic substitutions, and in stark contrast to their deterministic counterparts, subshifts of random substitutions often have positive topological entropy and exhibit uncountably many ergodic measures. Moreover, they have been shown to provide mathematical models for physical quasicrystals with defects.

We will begin by talking about subshifts generated by Sturmian words and ways to measure their complexity beyond topological entropy, and show how this measure of complexity can be used to build a classification via Jarník sets. We will then build a bridge between these subshifts and subshifts of random substitutions. We will conclude with some recent dynamical results on subshifts of random substitutions and ways to visualise these subshifts. Namely, we will present a method to build a new class of Rauzy fractals.

Apr 18

Thu

Giulio Del Zanna (University of Cambridge)

10:00

Thoughts on measuring elemental abundances in the solar atmosphere

Abstract:
I briefly review some methods and measurements of elemental abundances in the solar atmosphere, with emphasis on the transition region and corona. Some limitations in the methods, in the modelling of the spectral line intensities, and in the observations are discussed. Examples from the X-rays, the EUV, the UV, the visible and near-infrared are presented. A significant improvement in the modelling some of the ions is being made available with CHIANTI version 11. All the observations indicate that the solar corona has photospheric abundances and that the hot 3 MK active region cores have stable enhancements of a factor of about 3.2 in the ratios of low to high-FIP elements. A lot of uncertainties and puzzles still exist, requiring further analyses and, more importantly, future instrumentation.

Apr 18

Thu

Briony Eldridge (Southampton)

16:00

Loop Spaces of Polyhedral Products Associated with Substitution Complexes

Hicks Seminar Room J11

Abstract:
Polyhedral products are a topological space formed by gluing together ingredient spaces in a manner governed by a simplicial complex. They appear in many areas of study, including toric topology, combinatorics, commutative algebra, complex geometry and geometric group theory. A fundamental problem is to determine how operations on simplicial complexes change the topology of the polyhedral product. In this talk, we consider the substitution complex operation. We obtain a description of the loop space associated with some substitution complexes, and use this to build a new family of simplicial complexes such that the homotopy type of the loop space of the moment angle complex is a product of spheres and loops on spheres.

Apr 18

Thu

José Juan González Avilés (Universidad Nacional Autónoma de México)

Plasma Dynamics Group

16:00

Global MHD simulations of solar wind streams in the inner heliosphere using sunRunner3D

online / Google Meet

Abstract:
Understanding the large-scale three-dimensional structure of the inner heliosphere, while important in its own right, is crucial for space weather applications, such as forecasting the time of arrival and propagation of coronal mass ejections (CMEs). This study uses sunRunner3D (SR3D), a 3-D MHD model, to simulate solar wind (SW) streams and generate background states. SR3D employs the boundary conditions generated by CORHEL and the PLUTO code to compute the plasma properties of the SW with the magnetohydrodynamic (MHD) approximation up to 1.1 AU in the inner heliosphere. We demonstrate that SR3D reproduces global features of Corotating Interaction Regions (CIRs) observed by Earth-based spacecraft (OMNI) and STEREO-A for a set of Carrington rotations that cover a period that lays in the late declining phase of solar cycle 24. Additionally, we demonstrate that the model solutions are valid in the corotating and inertial frames of references. Moreover, a comparison between SR3D simulations and in-situ measurements shows reasonable agreement with the observations, and our results are comparable to those achieved by Predictive Science Inc.'s MAS code and SWASTi-SW framework.

Apr 19

Fri

Adrià Gómez Valent (Barcelona)

14:00

Is there still room for low-z solutions to the Hubble tension?

Hicks Seminar Room J11

Abstract:
The ∼5\sigma mismatch between the value of the Hubble parameter measured by SH0ES and the one inferred from the inverse distance ladder (IDL) constitutes the biggest tension afflicting the standard model of cosmology, which could be pointing to the need of physics beyond LCDM. In this talk I will review the background history required to solve the H0 tension if we consider standard prerecombination physics, paying special attention to the role played by the data on baryon acoustic oscillations (BAO) employed to build the IDL. I will show that the anisotropic BAO data favor an ultra-late-time (phantom-like) enhancement of H(z) at z<0.2, accompanied by a transition in the absolute magnitude of supernovae of Type Ia M(z) in the same redshift range. The effective dark energy (DE) density must be smaller than in the standard model at higher redshifts. Instead, when angular BAO data (claimed to be less subject to model dependencies) is employed in the analysis, the increase of H(z) must start at much higher redshifts, typically in the range z= 0.5-0.8. In this case, M(z) could experience also a transition (although much smoother) and the effective DE density becomes negative at z\sim 2. Both scenarios require a violation of the weak energy condition, but leave an imprint on completely different redshift ranges and might also have a different impact on the perturbed observables. They allow for the effective crossing of the phantom divide. I will put the accent on the utmost importance of the choice of the BAO data set in the study of the possible solutions to the H0 tension.

Apr 22

Mon

TBC

13:00

Hicks F41

Apr 22

Mon

Cheuk Yu Mak (Southampton)

14:00

Loop group action on symplectic cohomology

Hicks Seminar Room J11

Abstract:
For a compact Lie group G, its massless Coulomb branch algebra is the G-equivariant Borel-Moore homology of its based loop space. This algebra is the same as the algebra of regular functions on the BFM space. In this talk, we will explain how this algebra acts on the equivariant symplectic cohomology of Hamiltonian G-manifolds when the symplectic manifolds are open and convex. This is a generalization of the closed case where symplectic cohomology is replaced with quantum cohomology. Following Teleman, we also explain how it relates to the Coulomb branch algebra of cotangent-type representations. This is joint work with Eduardo González and Dan Pomerleano.

Apr 22

Mon

Cyril Closset (Birmingham)

15:00

Topologically twisted indices for any G

Hicks Seminar Room J11

Abstract:
We consider the A-model obtained by a partial topological twist of a 3d N=2 supersymmetric gauge theory. The twisted indices are the Witten indices over the Hilbert space of the 3d theory compactified on a closed Riemann surface, which generalise the Verlinde formulae. (In the special case of pure Chern-Simons theories – that is, 3d gauge theory without matter--, they give us the number of conformal blocks of the corresponding WZW model on the Riemann surface.) Previous physical methods only computed the twisted indices for a gauge group G that is simply connected and/or unitary. We generalise the supersymmetric computation to G any real compact Lie group, using the notion of higher-form symmetries. I will give a pedagogical presentation of our results. [Work to appear with Elias Furrer and Osama Khlaif.]

Apr 23

Tue

Johannes Droschl

13:00

On modular representations of $GL_n$ over a p-adic field

Hicks Seminar Room J11 / Google Meet

Abstract:
The Godement-Jacquet L-function is a classical invariant attached to irreducible representations of $GL_n$. Minguez extended their definition to representations over fields of characteristic $\ell\neq p$. In this talk we will finish the computation of these L-functions for modular representations and check that they agree with the L-function of their respective C-parameter defined by Kurinczuk and Matringe. We approach the problem by extending the theory of square-irreducible representations, and their derivatives, of Lapid and Minguez to modular representations and applying it to our setting.

Apr 24

Wed

Catherine Meusburger (University of Erlangen)

14:00

Dijkgraaf-Witten theory with defects

Hicks Seminar Room J11

Abstract:
We use 3d defect TQFTs to give a gauge theoretical formulation of (untwisted) Dijkgraaf-Witten TQFT with defects. This leads to a simple description in terms of embedding quivers, groupoids and their representations. Defect Dijkgraaf-Witten TQFTs is then formulated in terms of spans of groupoids and representations of spans. This is work in progress with João Faría-Martins, University of Leeds.

Apr 24

Wed

Elsa Teixeira (Montpellier)

15:00

Exploring Signatures of the Dark Sector through Fluid Approximations

Hicks Seminar Room J11

Abstract:
The persistent discrepancy between theoretical predictions of the standard cosmological model and precision measurements from diverse observational probes remains a pressing challenge in modern cosmology. Over the past decade, mounting evidence for persistent discrepancies in the inferred values of cosmological parameters derived from both model-dependent and -independent methodologies has motivated the proposal of alternatives to the standard paradigm. In this seminar, I will focus on the exploration of potential missing physics within the standard model, focusing on the enigmatic dark sector comprising dark matter and dark energy, and any potential interactions between them. Leveraging on fluid approximations for the physical nature of the dark sector and its underlying dynamics, we assess the viability of various models in reconciling the observed cosmological tensions.

Apr 26

Fri

Thomas Montandon (Montpellier)

15:00

Relativistic matter bispectrum of cosmic structure

Hicks Seminar Room J11

Abstract:
Upcoming surveys of cosmic structures will probe scales ranging from the nonlinear regime to scales close to the cosmological horizon. This opens up the possibility of probing the ΛCDM model, as well as early universe scenarios with non-Gaussianity. Modeling the galaxy bispectrum is challenging, as it involves general relativity, radiation, and large nonlinearities. In this talk, I will present the latest developments we have achieved in the numerical and theoretical modeling of the matter angular bispectrum on the light cone, including relativistic and radiation effects. This is a crucial step towards modeling the observable bispectra, i.e., the galaxy number count bispectrum and the weak lensing bispectrum.

Apr 29

Mon

Enrico Dell'Arra (Sheffield)

13:00

Hicks J11

Apr 29

Mon

Sukjoo Lee (Edinburgh)

14:00

Hodge number duality for orbifold Clarke mirror pairs via tropical geometry.

Hicks Seminar Room J11

Abstract:
Hodge number duality is one of the most fundamental phenomena in mirror symmetry. In the 1990s, Batyrev and Borisov introduced a combinatorial mirror construction for nef toric complete intersections of Calabi-Yau varieties, verifying Hodge number duality for these cases. Clarke has recently expanded this construction, broadening its scope to include a wide range of examples of mirror pairs. In this talk, I will discuss ongoing work with Andrew Harder, where we establish Hodge number duality for a large class of orbifold Clarke mirror pairs. We achieve this by developing a new tropical geometric tool to compute Hodge numbers. Our results not only confirm the result of Batyrev and Borisov but also lead to a proof of a conjecture by Katzarkov, Kontsevich, and Pantev for orbifold toric complete intersections. If time permits, I will also describe several applications, including the functoriality in Fano mirror symmetry and mirror symmetry for singular varieties.

Apr 29

Mon

Dylan Butson (Oxford)

15:00

W-algebras, Yangians, and Calabi-Yau threefolds

Hicks Seminar Room J11

Abstract:
I'll recall some basics about Slodowy slices, generalized slices in the affine Grassmannian, and quantizations thereof called W-algebras and Yangians, respectively, as well as their analogues for affine Lie algebras which are naturally described using the theory of vertex algebras. Then I'll explain a construction of vertex algebras associated to divisors in toric Calabi-Yau threefolds, which include affine W-algebras in type A for arbitrary nilpotents, and outline a dictionary between the geometry of the threefolds and the representation theory of these algebras. I'll also explain the physical interpretation of these results, as an example of twisted holography for M5 branes in the omega background.

Apr 30

Tue

Bence Hevesi (Kings College London)

13:00

Local-global compatibility at l=p for torsion automorphic Galois representations

Hicks Seminar Room J11 / Google Meet

Abstract:
Some ten years ago, Scholze proved the existence of Galois representations associated with torsion eigenclasses appearing in the cohomology of locally symmetric spaces for GL_n over imaginary CM fields. Since then, the question of local-global compatibility for these automorphic Galois representations has been an active area of research motivated by applications towards new automorphy lifting theorems. I will report on my work on local-global compatibility at l=p in this direction, generalising the results of the celebrated 10-author paper and Caraiani—Newton.

May 1

Wed

David Corfield (University of Kent)

14:00

Hicks Seminar Room J11

May 2

Thu

Sanja Danilovic (Institute for Solar Physics, Stockholm University, Sweden)

10:00

An overview of last October's SST-SolO observational campaign

Abstract:
We present the results of coordinated observations of the Swedish 1-m Solar Telescope with Solar Orbiter that took place from October 12th to 26th 2023. The campaign resulted in 7 datasets of various quality. The observational programs were adjusted to the seeing conditions. The observations cover two active regions and a coronal hole. We focus on the morphology and evolution of several targets that are observed from two vantage points. We share the lessons we learned and give an outline of our plans for October this year and the support we could give during remote sensing windows 16 and 17.

Web announcement:
https://espos.stream/2024/05/02/Danilovic/
———————————————————
Zoom link: https://zoom.us/j/165498165
(Meeting ID: 165 498 165)

May 2

Thu

Ehud Meir (Aberdeen)

16:00

Invariants that are covering spaces and their Hopf algebras

Hicks Seminar Room J11

Abstract:
Different flavours of string diagrams arise naturally in studying algebraic structures (e.g. algebras, Hopf algebras, Frobenius algebras) in monoidal categories. In particular, closed diagrams can be realized as scalar invariants. For a structure of a given type the closed diagrams form a commutative algebra that has a richer structure of a self dual Hopf algebra. This is very similar, but not quite the same, as the positive self adjoint Hopf algebras that were introduced by Zelevinsky in studying families of representations of finite groups. In this talk I will show that the algebras of invariants admit a lattice that is a PSH-algebra. This will be done by considering maps between invariants, and realizing them as covering spaces. I will then show some applications to subgroup growth questions, and a formula that relates the Kronecker coefficients to finite index subgroups of free groups.

May 7

Tue

Jay Taylor (Manchester)

13:00

Hicks Seminar Room J11 / Google Meet

May 8

Wed

Rohini Ramadas (University of Warwick)

14:00

Complex dynamics via algebraic geometry

Hicks Seminar Room J11

Abstract:
Complex dynamics began in the early 1900s with the study of iterating polynomial functions with complex coefficients. This simple idea gives rise to beautiful fractal pictures such as the Mandelbrot set, as well as interesting mathematical questions of many different flavours (algebraic, analytic, topological, arithmetic, etc.). The field gained momentum in the 1980s due to work of Thurston, Douady-Hubbard, Sullivan, and others, connecting these dynamical questions to surface topology and the theory of 3-manifolds. The last decade has seen many breakthroughs achieved via new tools from number theory, measure theory and algebraic geometry. I will discuss some of these recent developments, highlighting the interplay between topology on one hand and algebraic geometry/number theory on the other hand.

May 8

Wed

Gabriele Barca (Rome/Sheffield)

15:15

Hicks Seminar Room J11

May 8

Wed

Alessandro Chiarini (OIST, Okinawa, Japan)

Fluid Dynamics Seminar

16:00

Finite-size inertial spherical particles in homogeneous isotropic turbulence

Diamond LT2

Abstract:
We use direct numerical simulations to study the fluid-solid interaction of non-dilute suspensions of spherical particles in homogeneous isotropic turbulence. I will discuss how finite-size inertial spherical particles modulate turbulence, and how they preferentially accumulate in specific regions of the flow. In particular, we observe that particles of different size and density modulate the flow in a different way. For small and heavy particles, the classical energy cascade is inhibited, and the energy transfer across scales is essentially driven by the fluid-solid interaction. We also find that particles of different size and density have a different level of clustering. I will discuss their collective motion and preferential location in relation with properties of the carrier flow.

May 9

Thu

Georg Struth (Sheffield)

16:00

Single-set Cubical Categories and Their Formalisation with a Proof Assistant

Hicks Seminar Room J11

Abstract:
Cubical sets and cubical categories are widely used in mathematics and computer science, from homotopy theory to homotopy type theory, higher-dimensional automata and, last but not least, higher-dimensional rewriting, where our own interest in these structures lies. To formalise cubical categories with the Isabelle/HOL proof assistant along the path of least resistance, we take a single-set approach to categories, which leads to new axioms for cubical categories. Taming the large number of initial candidate axioms has relied essentially on Isabelle's proof automation. Yet we justify their correctness relative to the standard axiomatisation by Al Agl, Brown and Steiner via categorical equivalence proofs outside of Isabelle. In combination, these results present a case study in experimental mathematics with a proof assistant. In this talk I will focus on the formalisation experience -- lights and shadows -- and conclude with some general remarks about formalised mathematics. This is joint work with Philippe Malbos and Tanguy Massacrier (Université Claude Bernard Lyon 1).

May 13

Mon

TBC

13:00

Hicks J11

May 15

Wed

Álvaro Álvarez Domínguez (Madrid)

15:15

Hicks Seminar Room J11

May 17

Fri

Matteo Sacchi (Oxford)

14:00

Hicks Seminar Room J11

May 17

Fri

Phillip Engel (Bonn)

16:00

Hicks Seminar Room J11

May 20

Mon

Juan Morales (Glasgow)

13:00

Hicks Seminar Room J11

May 21

Tue

Owen Patashnick (Kings College London)

13:00

Hicks Seminar Room J11 / Google Meet

May 23

Thu

Nika Shakiba (British Columbia)

11:00

TBC

Hicks Seminar Room J11

May 24

Fri

Clare Rees-Zimmerman (University of Oxford)

SIAM-IMA Chapter Seminar

16:00

Modelling paint drying: controlling particle arrangement with diffusiophoresis

Hicks Seminar Room J11

Abstract:
Stratification in drying films – how a mixture of differently-sized particles arranges itself upon drying – is examined. Being able to control this would allow the design of coating formulations which self-assemble during drying to give a desired structure. Potential applications are across a range of industries, from a self-layering car paint, to a biocidal coating in which the biocide stratifies to the top surface, where it is required. Diffusiophoresis is the migration of particles along a concentration gradient of a different solute species. Diffusiophoresis can be caused by different mechanisms, two of which are investigated here: excluded volume and electrolyte-driven diffusiophoresis. A continuum hydrodynamic model is derived, and the resulting partial differential equations solved numerically. Asymptotic solutions are found for high evaporation rate. It is found that the final film structure is governed by the relative magnitudes of the diffusive and diffusiophoretic terms. The diffusiophoretic term promotes small-on-top stratification, and so may account for experimental observations of accumulated small particles at the top surface of dried films. In the case of electrolyte-driven diffusiophoresis, two methods are discovered to control the resulting stratification: (i) setting the surface charge on the particles, and (ii) setting the background salt concentration.

May 29

Wed

Lucia Menendez-Pidal (Madrid)