Found at least 20 result(s)

01.01.1970 (Thursday)

GE' style='color:#f0ad4e'>GE 227' style='color:#f0ad4e'>Rational homology spheres and SL(2,C) representations

regular seminar Steven Sivek (Imperial College London )

at:
01:00 - 01:00
KCL, Strand
room: S4.29
abstract:

Building on non-vanishing theorems of Kronheimer and Mrowka in instanton Floer homology, Zentner proved that if Y is a homology 3-sphere other than S^3, then its fundamental group admits a homomorphism to SL(2,C) with non-abelian image. In this talk, Iâll explain how to generalize this to any Y whose first homology is 2-torsion or 3-torsion, other than the connect sum of n copies of the three-dimensional real projective space for any n or lens spaces of order 3. This is joint work with Sudipta Ghosh and Raphael Zentner.

Keywords:

01.01.1970 (Thursday)

PR' style='color:#f0ad4e'>PR 217' style='color:#f0ad4e'>KCL Probability Seminar: Directed Spatial Permutations on Asymmetric Tori

regular seminar Tyler Hellmuth (Durham University)

at:
01:00 - 01:00
KCL, Strand
room: S4.29
abstract:

Random permutations show up in a variety of areas in mathematics and its applications. In connection with physical applications (e.g., the lambda transition for superfluid helium), there is an interest in random spatial permutations -- that is, laws on permutations that have a 'geometric bias'. There are compelling heuristic arguments that this spatial bias has little effect on the distribution of the largest cycles of a random spatial permutation, provided that large cycles actually exist. I'll discuss a particular model of random spatial permutations (directed permutations on asymmetric tori) where these heuristics can be made precise, and large cycles can be shown to follow the expected (Poisson-Dirichlet) law.

Keywords:

01.01.1970 (Thursday)

TP' style='color:#f0ad4e'>TP 102584' style='color:#f0ad4e'>Lonti: The initial (boundary) value problem in numerical general relativity

Regular Seminar Pau Figueras (QMUL)

at:
01:00 - 01:00
KCL Strand
room: LIMS
abstract:

In these series of lectures we will explore initial value problem in general relativity and how it can be solved in a computer in practical situations. We will first cover the necessary mathematical foundations, including the concepts of well-posedness and strong hyperbolicity, and then explore the current formulations of Einsteinââ¬â¢s theory of gravity that are implemented in modern numerical codes, namely generalised harmonic coordinates and the BSSN formulation. We shall see how the latter can be implemented in a toy code so as to get some hands on experience. Time permitting, we will also explore the initial boundary value problem in asymptotically anti-de Sitter spaces and how it can be solved in practice using the characteristic formulation of the Einstein equations in applications of holography.

Keywords:

01.01.1970 (Thursday)

TP' style='color:#f0ad4e'>TP 232' style='color:#f0ad4e'>TBA

journal club Maneerat Chawakorn (KCL)

at:
01:00 - 01:00
KCL, Strand
room: Norfolk Building 342N
abstract:

Keywords:

01.01.1970 (Thursday)

ST' style='color:#f0ad4e'>ST 235' style='color:#f0ad4e'>Variational Inference for Cutting Feedback in Misspecified Models

regular seminar Michael Smith (University of Melbourne)

at:
01:00 - 01:00
KCL, Strand
room: S5.20
abstract:

Bayesian analyses combine information represented by different terms in a joint Bayesian model. When one or more of the terms is misspecified, it can be helpful to restrict the use of information from suspect model components to modify posterior inference. This is called âœcutting feedbackâ, and both the specification and computation of the posterior for such âœcut modelsâ is challenging. In this paper, we define cut posterior distributions as solutions to constrained optimization problems, and propose variational methods for their computation. These methods are faster than existing Markov chain Monte Carlo (MCMC) approaches by an order of magnitude. It is also shown that variational methods allow for the evaluation of computationally intensive conflict checks that can be used to decide whether or not feedback should be cut. Our methods are illustrated in examples, including an application where recent methodological advances that combine variational inference and MCMC within the variational optimization are used.

Keywords:

01.01.1970 (Thursday)

AN' style='color:#f0ad4e'>AN 237' style='color:#f0ad4e'> Spectral properties of random matrices with heavy-tailed entries

regular seminar Svetlana Malysheva (Queen Mary University of London)

at:
01:00 - 01:00
KCL, Strand
room: S5.20
abstract:

The talk will outline the main properties of high-dimensional random matrices whose entries do not have the 4th moment. We will also discuss heavy-tailed random matrices obtained from stock returns.

Keywords:

01.01.1970 (Thursday)

ME' style='color:#f0ad4e'>ME 208' style='color:#f0ad4e'>Maths education seminar: Investigating and Improving Proof Comprehension

regular seminar Lara Alcock (Loughborough University)

at:
01:00 - 01:00
KCL, Strand
room: K0.50
abstract:

Undergraduate mathematics students see a lot of written proofs. But how much do they learn from them? Perhaps not as much as we would like, and perhaps we would like to improve their ability to engage with mathematics by reading. This talk will present a sequence of research studies addressing this issue. It will first describe studies on e-Proofs, which attempted to improve comprehension via proof-specific learning resources. It will then describe an eye-tracking study that provided real-time data on both student and expert mathematical reading. Finally, it will describe the effects of generic mathematical self-explanation training, investigated via both experimental and eye-tracking methods. Together, these studies provide insight into what is special about mathematical reading, and how students can be supported in reading more effectively.

Keywords:

01.01.1970 (Thursday)

GE' style='color:#f0ad4e'>GE 236' style='color:#f0ad4e'>Non-archimedean periods for log Calabi-Yau surfaces

regular seminar Soham Karwa (Imperial College London)

at:
01:00 - 01:00
KCL, Strand
room: S4.29
abstract:

Period integrals are a fundamental concept in algebraic geometry and number theory. In this talk, we will study the notion of non-archimedean periods as introduced by Kontsevich and Soibelman. We will give an overview of the non-archimedean SYZ program, which is a close analogue of the classical SYZ conjecture in mirror symmetry. Using the non-archimedean SYZ fibration, we will prove that non-archimedean periods recover the analytic periods for log Calabi-Yau surfaces, verifying a conjecture of Kontsevich and Soibelman. This is joint work with Jonathan Lai.

Keywords:

01.01.1970 (Thursday)

PR' style='color:#f0ad4e'>PR 216' style='color:#f0ad4e'>KCL Probability Seminar: Random walks in dynamic environments.

regular seminar Guillaume Conchon-Kerjan (King's College London)

at:
01:00 - 01:00
KCL, Strand
room: S4.29
abstract:

At the boundary of (discrete) probability and statistical physics, random walks in dynamic environments represent a way to model a particle advected by a fluid. Though some models are quite simple to define (usually, the environment is an evolving particle system, such as the exclusion process or a "cloud" of random walks), interest for this topic among probabilists has strongly increased in the past decade. These models feature complex technical challenges, as the time-dependency of the environment totally reshuffles the structure of space-time correlations, compared to the more classical setting of walks in static environment. In this talk, we will present this context and highlight how some key features such as recurrence/transience or the fluctuations of the walker are still the subject of many conjectures.

Keywords:

01.01.1970 (Thursday)

TP' style='color:#f0ad4e'>TP 225' style='color:#f0ad4e'>BPS Ensembles of Strings and Fivebranes

regular seminar Zigdon Yoav ()

at:
01:00 - 01:00
KCL, Strand
room: K0.17
abstract:

We study ensembles of 1/2-BPS bound states of fundamental strings and NS-fivebranes (NS5-F1) in the decoupling limit. We revisit a solution corresponding to an ensemble average of these bound states, and find that the appropriate duality frame for describing the near-source structure is the T-dual NS5-P frame.
When members of the ensemble spin with two fixed angular potentials about two orthogonal planes, our main result is that an ensemble average of them gives rise to a smooth horizonless solution characterized by an ellipsoidal structure. This contrasts with ring structures obtained when fixing the angular momenta instead of the angular potentials\DSEMIC we trace this difference of ensembles to large fluctuations of the angular momentum in the ensemble of fixed angular potential.

Keywords:

01.01.1970 (Thursday)

TP' style='color:#f0ad4e'>TP 102583' style='color:#f0ad4e'>Lonti: The initial (boundary) value problem in numerical general relativity

Regular Seminar Pau Figueras (QMUL)

at:
01:00 - 01:00
KCL Strand
room: LIMS
abstract:

In these series of lectures we will explore initial value problem in general relativity and how it can be solved in a computer in practical situations. We will first cover the necessary mathematical foundations, including the concepts of well-posedness and strong hyperbolicity, and then explore the current formulations of Einsteinââ¬â¢s theory of gravity that are implemented in modern numerical codes, namely generalised harmonic coordinates and the BSSN formulation. We shall see how the latter can be implemented in a toy code so as to get some hands on experience. Time permitting, we will also explore the initial boundary value problem in asymptotically anti-de Sitter spaces and how it can be solved in practice using the characteristic formulation of the Einstein equations in applications of holography.

Keywords:

01.01.1970 (Thursday)

TP' style='color:#f0ad4e'>TP 233' style='color:#f0ad4e'>Towards black hole states

journal club Simon Ekhammar (KCL)

at:
01:00 - 01:00
KCL, Strand
room: Norfolk Building 342N
abstract:

I will discuss the problem of counting states in superconformal field theories, focusing on 4D N=4 SYM. The main focus will be on reviewing background material before briefly commenting on some recent developments in 2306.04693 and 2209.06728. I also hope to make some comments on the history of the problem.

Keywords:

01.01.1970 (Thursday)

ST' style='color:#f0ad4e'>ST 229' style='color:#f0ad4e'>Unsupervised attack pattern detection in honeypot data using Bayesian topic modelling

regular seminar Francesco Sanna Passino (Imperial College London)

at:
01:00 - 01:00
KCL, Strand
room: S5.20
abstract:

Cyber-systems are under near-constant threat from intrusion attempts. Attacks types vary, but each attempt typically has a specific underlying intent, and the perpetrators are typically groups of individuals with similar objectives. Clustering attacks appearing to share a common intent is very valuable to threat-hunting experts. This talk explores topic models for clustering terminal session commands collected from honeypots, which are special network hosts designed to entice malicious attackers. The main practical implications of clustering the sessions are two-fold: finding similar groups of attacks, and identifying outliers. A range of statistical topic models are considered, adapted to the structures of command-line syntax. In particular, concepts of primary and secondary topics, and then session-level and command-level topics, are introduced into the models to improve interpretability. The proposed methods are further extended in a Bayesian nonparametric fashion to allow unboundedness in the vocabulary size and the number of latent intents. The methods are shown to discover an unusual MIRAI variant which attempts to take over existing cryptocurrency coin-mining infrastructure, not detected by traditional topic-modelling approaches. This is joint work with Daniyar Ghani (Imperial College London), Anastasia Mantziou (Alan Turing Institute), Philip Thiede (formerly at Imperial College London, now at Abios), Ross Bevington (Microsoft), Nicholas A. Heard (Imperial College London).

Keywords:

01.01.1970 (Thursday)

AN' style='color:#f0ad4e'>AN 230' style='color:#f0ad4e'>Existence results for the Landau equation

regular seminar Amélie Loher (University of Cambridge)

at:
01:00 - 01:00
KCL, Strand
room: S5.20
abstract:

We consider the Landau equation with Coulomb potentials. We discuss a global existence result close to equilibrium and a short time existence result for general data. In both cases we take initial data in unweighted Lp spaces for p > 3/2. We thus work with the weakest class of initial data that has been considered until now. This is joint work with William Golding (UT Austin) and Maria Gualdani (UT Austin).

Keywords:

01.01.1970 (Thursday)

TP' style='color:#f0ad4e'>TP 102609' style='color:#f0ad4e'>Initial Boundary Value Problem For Vacuum Einstein Equations

Regular Seminar Zhongshan An (U. Michigan)

at:
01:00 - 01:00
KCL Strand
room: ONLINE or S0.12
abstract:

**Send email to jeremy.mann@kcl.ac.uk for link to online seminar.** In general relativity, spacetime metrics satisfy the Einstein equations, which are wave equations in the harmonic gauge. The Cauchy problem for the vacuum Einstein equations has been well-understood since the work of Choquet-Bruhat. For an initial data set satisfying the vacuum constraint equations, there exists a solution to the vacuum Einstein equations and it is geometrically unique in the domain of dependence of the initial surface. On contrast, the initial boundary value problem (IBVP) has been much less understood. To solve for an vacuum metric in a region with time-like boundary, one needs to impose boundary conditions to guarantee geometric uniqueness of the solution. However, due to gauge issues occurring on the boundary, there has not been a satisfying choice of boundary conditions. In this talk I will discuss obstacles in establishing a well-defined IBVP for vacuum Einstein equations and the geometric uniqueness problem. Then I will talk about an existence and geometric uniqueness result in a joint work with Michael Anderson.

Keywords:

01.01.1970 (Thursday)

ME' style='color:#f0ad4e'>ME 207' style='color:#f0ad4e'>Maths education seminar: Alternative assessments of Mathematical Proof

regular seminar Robbie Bickerton (University of Edinburgh)

at:
01:00 - 01:00
KCL, Strand
room: K0.50
abstract:

The purpose of this talk is to introduce a practical method for assessing mathematical proof online. We examine the effect of faded worked examples and reading comprehension questions to student's understanding of proof. By breaking down a given proof, we will demonstrate a checklist that can be used to generate comprehension questions which can be assessed automatically online. We then provide some preliminary results of deploying such questions.
In addition, we shall examine several examples of proof comprehension questions that have been created by following this checklist. In particular, I will discuss some ongoing work related to the creation of proof comprehension tasks used to assessment of proof in a higher-level undergraduate pure mathematics courses.

Keywords:

01.01.1970 (Thursday)

GE' style='color:#f0ad4e'>GE 231' style='color:#f0ad4e'>MMP for toric foliations

regular seminar Yen-An Chen (Imperial College London)

at:
01:00 - 01:00
KCL, Strand
room: S4.29
abstract:

In recent years, significant progress has been made in the field of birational geometry for foliations. Notably, the Minimal Model Program (MMP) has been shown to work for foliations on threefolds. In this talk, I will demonstrate that the MMP is applicable to toric foliations as well. Specifically, I will discuss how non-dicritical singularities (and foliated dlt singularities if time permits) are preserved under the MMP. This is a joint work with Chih-Wei Chang.

Keywords:

01.01.1970 (Thursday)

PR' style='color:#f0ad4e'>PR 215' style='color:#f0ad4e'>KCL Probability Seminar: When is a critical Random intersection graph different from a Erdos-Renyi one?

regular seminar Minmin Wang (University of Sussex)

at:
01:00 - 01:00
KCL, Strand
room: S4.29
abstract:

Random intersection graph is a simple random graph model that incorporates community structures. To build such a graph, imagine there are n individuals and m potential communities, where each individual joins a community independently with probability p. Two individuals are adjacent to each other in the random intersection graph G(n, m, p) if and only if they belong to a common community. It is known that if m>>n^3, then the model is asymptotically equivalent to an Erdos-Renyi graph G(n, q) with a suitable q. Iâll discuss other ways to compare the two models, particularly regarding the scaling limit of the graphs inside the critical window and number of triangles found in the large components.

Keywords:

01.01.1970 (Thursday)

TP' style='color:#f0ad4e'>TP 102582' style='color:#f0ad4e'>Lonti: The initial (boundary) value problem in numerical general relativity

Regular Seminar Pau Figueras (QMUL)

at:
01:00 - 01:00
KCL Strand
room: LIMS
abstract:

In these series of lectures we will explore initial value problem in general relativity and how it can be solved in a computer in practical situations. We will first cover the necessary mathematical foundations, including the concepts of well-posedness and strong hyperbolicity, and then explore the current formulations of Einsteinââ¬â¢s theory of gravity that are implemented in modern numerical codes, namely generalised harmonic coordinates and the BSSN formulation. We shall see how the latter can be implemented in a toy code so as to get some hands on experience. Time permitting, we will also explore the initial boundary value problem in asymptotically anti-de Sitter spaces and how it can be solved in practice using the characteristic formulation of the Einstein equations in applications of holography.

Keywords:

01.01.1970 (Thursday)

ST' style='color:#f0ad4e'>ST 228' style='color:#f0ad4e'>A journey through model-based clustering with intractable distributions

regular seminar Riccardo Corradin (University of Nottingham)

at:
01:00 - 01:00
KCL, Strand
room: S5.20
abstract:

Model-based clustering represents one of the fundamental procedures in a statistician's toolbox. Within the model-based clustering framework, we consider the case where the kernel distribution of nonparametric mixture models is available only up to an intractable normalizing constant, in which most of the commonly used Markov chain Monte Carlo methods fail to provide posterior inference. To overcome this problem, we propose an approximate Bayesian computational strategy, whereby we approximate the posterior to avoid the intractability of the kernel. By exploiting the structure of the nonparametric prior, our proposal combines the use of predictive distributions as a proposal with transport maps to obtain an efficient and flexible sampling strategy. Further, we illustrate how the specification of our proposal can be relaxed by introducing an adaptive scheme on the degree of approximation of the posterior distribution. Empirical evidence from simulation studies shows that our proposal outperforms its main competitors in terms of computational times while preserving comparable accuracy of the estimates.

Keywords: