Fri, 05 May 2017
14:15
C3

Sub-ice phytoplankton blooms in the Arctic Ocean

David Rees Jones
(Oxford Earth Science)
Abstract

In July 2011, the observation of a massive phytoplankton bloom underneath a sea ice–covered region of the Chukchi Sea shifted the scientific consensus that regions of the Arctic Ocean covered by sea ice were inhospitable to photosynthetic life. Although the impact of widespread phytoplankton blooms under sea ice on Arctic Ocean ecology and carbon fixation is potentially marked, the prevalence of these events in the modern Arctic and in the recent past is, to date, unknown. We investigate the timing, frequency, and evolution of these events over the past 30 years. Although sea ice strongly attenuates solar radiation, it has thinned significantly over the past 30 years. The thinner summertime Arctic sea ice is increasingly covered in melt ponds, which permit more light penetration than bare or snow-covered ice. We develop a simple mathematical model to investigate these physical mechanisms. Our model results indicate that the recent thinning of Arctic sea ice is the main cause of a marked increase in the prevalence of light conditions conducive to sub-ice blooms. We find that as little as 20 years ago, the conditions required for sub-ice blooms may have been uncommon, but their frequency has increased to the point that nearly 30% of the ice-covered Arctic Ocean in July permits sub-ice blooms. Recent climate change may have markedly altered the ecology of the Arctic Ocean.

The British Applied Mathematics Colloquium (BAMC), held this year at the University of Surrey, has awarded its two talk prizes to Oxford Mathematicians Jessica Williams and Graham Benham. Their colleague in Oxford Mathematics Ian Roper won the poster prize.

Oxford Mathematician Doireann O'Kiely has been awarded the biennial Lighthill-Thwaites Prize for her work on the production of thin glass sheets. The prize is awarded by the Institute of Mathematics and its Applications to researchers who have spent no more than five years in full-time study or work since completing their undergraduate degrees.

Thu, 18 May 2017
12:00
L4

Diffusion-approximation for some hydrodynamic limits

Julien Vovelle
(Université Claude Bernard Lyon 1)
Abstract

We determine the hydrodynamic limit of some kinetic equations with either stochastic Vlasov force term or stochastic collision kernel. We obtain stochastic second-order parabolic equations at the limit. In the regime we consider, we also observe (or do not observe) some phenomena of enhanced diffusion. Joint works with Nils Caillerie, Arnaud Debussche, Martina Hofmanová.
 

Mon, 24 Apr 2017

14:15 - 15:15
L4

Soliton resolution conjecture

Roland Grinis
(Oxford)
Abstract

We will give an overview of the Soliton Resolution Conjecture, focusing mainly on the Wave Maps Equation. This is a program about understanding the formation of singularities for a variety of critical hyperbolic/dispersive equations, and stands as a remarkable topic of research in modern PDE theory and Mathematical Physics. We will be presenting our contributions to this field, elaborating on the required background, as well as discussing some of the latest results by various authors.

Fri, 19 May 2017

10:00 - 11:00
L4

Neutron reflection from mineral surfaces: Through thick and thin

Stuart Clarke
(BP Institute at Cambridge University)
Abstract

Conventional neutron reflection is a very powerful tool to characterise surfactants, polymers and other materials at the solid/liquid and air/liquid interfaces. Usually the analysis considers molecular layers with coherent addition of reflected waves that give the resultant reflected intensity. In this short workshop talk I will illustrate recent developments in this approach to address a wide variety of challenges of academic and commercial interest. Specifically I will introduce the challenges of using substrates that are thick on the coherence lengthscale of the radiation and the issues that brings in the structural analysis. I also invite the audience to consider if there may be some mathematical analysis that might lead us to exploit this incoherence to optimise our analysis. In particular, facilitating the removal of the 'background substrate contribution' to help us focus on the adsorbed layers of most interest.

Tue, 09 May 2017
14:30
L3

Ill-conditioning and numerical stability in radial basis functions (RBFs) using frame theory

Cécile Piret
(Michigan Technological University)
Abstract

We analyse the numerical approximation of functions using radial basis functions in the context of frames. Frames generalize the notion of a basis by allowing redundancy, while being restricted by a so-called frame condition. The theory of numerical frame approximations allows the study of ill-conditioning, inherently due to their redundancy, and suggests discretization techniques that still offer numerical stability to machine precision. We apply the theory to radial basis functions.

 

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