Mathematics colloquia

These are Mathematics Colloquia suitable for anyone.

Seminar details

Day: Wednesdays or Fridays.
Open to: Staff, students and the public.

For further information, please contact the organiser Dr Bin Cheng.

Upcoming seminars

Speaker: Valerio Lucarini (Reading)

Tuesday 3 December 2pm-3pm, 39AA04

Title
Global Stability Properties of the Climate: Melancholia States, Invariant Measures, and Phase Transitions

Abstract
For a wide range of values of the incoming solar radiation, the Earth features at least two attracting states, which correspond to competing climates. The warm climate is analogous to the present one; the snowball climate features global glaciation and conditions that can hardly support life forms. Paleoclimatic evidences suggest that in past our planet flipped between these two states. The main physical mechanism responsible for such instability is the ice-albedo feedback. Following an idea developed by Eckhardt and co. for the investigation of multistable turbulent flows, we study the global instability giving rise to the snowball/warm multistability in the climate system by identifying the climatic edge state, a saddle embedded in the boundary between the two basins of attraction of the stable climates. We refer to these states as Melancholia States. We then introduce random perturbations as modulations to the intensity of the incoming solar radiation. We observe noise-induced transitions between the competing basins of attractions. In the weak noise limit, large deviation laws define the invariant measure and the statistics of escape times. By empirically constructing the instantons, we show that the Melancholia states are the gateways for the noise-induced transitions. In the region of multistability, in the zero-noise limit, the measure is supported only on one of the competing attractors. For low (high) values of the solar irradiance, the limit measure is the snowball (warm) climate. The changeover between the two regimes corresponds to a first order phase transition in the system. The framework we propose seems of general relevance for the study of complex multistable systems. Finally, we propose a new method for constructing Melancholia states from direct numerical simulations, thus bypassing the need to use the edge-tracking algorithm.
Refs.

V. Lucarini, T. Bodai, Transitions across Melancholia States in a Climate Model: Reconciling the Deterministic and Stochastic Points of View, Phys. Rev. Lett. 122,158701 (2019)
V. Lucarini, T. Bodai, Edge States in the Climate System: Exploring Global Instabilities and Critical Transitions, Nonlinearity 30, R32 (2017) 

 

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Speaker: Niall MacKay (York)

Wednesday 11 December 2pm-3pm, 39AA04

Title
Weighing the Fog of War: a physicist's adventures in operations research and history

Abstract
A tour through ten years' work with operations researchers and historians on combat modelling, military history and their interaction. I'll begin with some elementary ideas from Lanchester theory and present some neat results for multilateral models. Then I shall describe some of our historical work, including on the First World War at sea and the Second World War in the air.

 

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Speaker: Mark Holland (Exeter)

Wednesday 6 November 2:30pm-3:30pm, 39AA04

Title
On extreme and record events in dynamical systems.

Abstract 

Understanding extreme events, such as severe weather, climatic or financial events is a major challenge. In this talk I will explain some of the mathematical approaches used in understanding extreme events, such as finding their probability distribution. We will assume that the underlying time series process is modelled by a deterministic dynamical system, such as a discrete time map or differential equation. These latter processes have some dependency, and so any results known about extremes for independent, identically distributed (i.i.d) random processes cannot immediately be transferred to dynamical systems. As part of the talk, I will review relevant extreme value theory associated to the i.i.d case. I will then discuss this theory for dynamical systems, illustrating with examples from low dimensional chaotic maps.

Past seminars

A partial overview of the recent trends in the mathematical analysis of deep learning
Speaker: Stephane Chretien (NPL)
Time: 3pm - 4pm
Date: Wednesday 22 May 2019
Venue: 22AA04
Abstract: Find out more.

On the Enumeration of Irreducible Polynomials over Finite Fields with Prescribed Coefficients
Speaker: Robert Granger (Surrey, Computing)
Time: 3pm - 4pm
Date: Friday 17 May 2019
Venue: 39AA04
Abstract: Find out more.

Next generation neural field modelling
Speaker: Stephen Coombes (Nottingham)
Time: 3pm - 4pm
Date: Friday 10 May 2019
Venue: 39AA04
Abstract: Find out more.

Application of complex analysis to the geometry of river valleys and networks
Speaker: Prof Robb McDonald (University College London)
Time: 3pm - 4pm
Date: Wednesday 20 February 2019
Venue: TBA
Abstract: Find out more

Fast Stretching of Paired Vortex Filaments in Axisymmetric and General Geometry
Speaker: Andrew Gilbert (Exeter)
Time: 3pm - 4pm
Date: Friday 08 February 2019
Venue: 39AA04
Abstract: Find out more

Cole-Hopf transform and its extension to the Navier-Stokes equations
Speaker: Prof Koji Ohkitani, University of Sheffield
Time: 3pm - 4pm
Date: Wednesday 16 January 2019
Venue: 39 AA 04
Abstract: Find out more.

Generating new physics models from machine learning
Speaker: Dr Sven Krippendorf, University of Munich
Time: 1:30pm - 2:30pm
Date: Wednesday 14 November 2018
Venue: 22 AA 04
Abstract: Find out more.

Strength in numbers: How demographic noise can reverse the direction of selection
Speaker: Dr Tim Rogers, University of Bath
Time: 4pm - 5pm
Date: Wednesday 31 October 2018
Venue: 22 AA 04
Abstract: Find out more.

Sets of integers containing (almost) arithmetic progressions
Speaker: Dr Jonathan Fraser, University of St Andrews
Time: 4pm - 5pm
Date: Wednesday 24 October 2018
Venue: 22 AA 04
Abstract: Find out more.

Cryptography using group theory
Speaker: Prof Simon Blackburn, Royal Holloway University of London
Time: 3pm - 4pm
Date: Wednesday 17 October 2018
Venue: 22 AA 04
Abstract: Find out more.

Quantum mechanics and Riemann hypothesis
Speaker: Prof Dorje Brody
Time: 12 noon - 1pm
Date: Friday 8 June 2018
Venue: 39 AA 04
Abstract: Find out more.

From gauge theory to higher gauge theory
Speaker: Dr Christian Saemann (Heriot-Watt University)
Time: 3pm - 4pm
Date: Wednesday 30 May 2018
Venue: 39 AA 04
Abstract: Find out more.

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AA Building, floor 4
University of Surrey
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