Mon 14/09/15 14:00 Fulton G20 Mathematics Seminar  Dr. Anthony Yeates (Durham University) Datadriven modelling of the Sun's magnetic field  abstractAbstractI will discuss issues in trying to reconstruct the magnetic field structure in the solar atmosphere based on limited magnetic observations on the solar surface. This effort is important not only for understanding the Sun itself but also for modelling and predicting space weather. The crux of the problem is inverting Faraday's law to determine the electric field from observations of only the magnetic field. hide 

Mon 21/09/15 14:00 Fulton G20 Mathematics Seminar  Dr. Rastko Sknepnek (University of Dundee) Flocks on a sphere: Effects of curvature on active collective motion  abstractAbstractIn this talk we show that coupling to curvature has profound effects on collective motion in active systems, leading to patterns not observed in flat space. Biological examples of such active motion in curved environments are numerous: curvature and tissue folding are crucial during gastrulation, epithelial and endothelial cells move on constantly growing, curved crypts and vili in the gut, and the mammalian corneal epithelium grows in a steadystate vortex pattern. Using Brownian dynamics simulations, we study a model of selfpropelled particles with polar alignment on a sphere. Hallmarks of these motion patterns are a polar vortex and a circulating band arising due to the incompatibility between spherical topology and uniform motion  a consequence of the hairy ball theorem. Furthermore, inspired by recent experiments of Baush and Dogic groups on droplets coated with actively driven microtubule bundles, we address active nematic systems confined to the surface of a sphere. hide 

Tue 29/09/15 14:00 Baxter Suite 1st Floor Tower  Careers Advisors (Mathematics Careers Day) University of Dundee  

Tue 06/10/15 14:00 Fulton G20 Mathematics Seminar  Prof. Charalambos Makridakis (University of Sussex) Self adaptive computational methods for nonlinear phenomena  abstractAbstractThe computation of singular phenomena (shocks, defects, dislocations, interfaces, cracks) arises in many complex systems. For computing such phenomena, it is natural to seek methods that are able to detect them and to devote the necessary computational recourses to their accurate resolution. At the same time, we would like to have mathematical guarantees that our computational methods approximate physically relevant solutions. Our purpose in this talk is to review results and discuss related computational challenges for such nonlinear problems modeled by PDEs. In addition we shall discuss issues related to Micro / Macro adaptive modeling and methods, in particular related to atomistic/continuum coupling in crystalline materials. hide 

Mon 12/10/15 14:00 Fulton G20 Mathematics Seminar  Dr. Andrew Hillier (DAMTP  Cambridge University) Prominences, the magnetic RayleighTaylor instability and what we can learn about the prominence magnetic field  abstractAbstractObservations by the Hinode satellite of quiescent prominences have revealed in great detail the dynamics of plumes rising through the prominence material. These plumes, created by the magnetic RayleighTaylor instability, rise through the prominence material. In this talk I will show how the growth rate for the linear instability and the nonlinear dynamics of the rising plume in the nonlinear regime provide diagnostic tools for investigating both the plasma beta and the magnetic field direction in the prominence. These methods will be compared to observations of plumes with both Doppler velocity and magnetic field measurements (both strength and direction) by Orozco Suarez et al (2014) to confirm their validity. It is through application of these new methods that I believe we will be able to make great strides in understanding the role of the magnetic field in the smallscale dynamics of quiescent prominences without the need for complex polarization measurements. hide 

Mon 19/10/15 14:00 Fulton G20 Mathematics Seminar  Dr. Omar Lakkis (University of Sussex) PDEs of MongeAmpère type and their numerical approximation  abstractAbstractThis talk is directed to a general audience, I will thus spend some time on the historical and mathematical background of the MongeAmpère partial differential equation and its relation to optimal mass transportation and geometric problems (including classical geometric optics as a surprising link between the two disciplines). In a second, more technical part I will brief on the various numerical methods, with a focus on the Nonvariational Finite Element Method, developed as a joint work with Tristan Pryer (Reading) and Ellya Kawecki (Oxford). hide 

Mon 26/10/15 14:00 Fulton G20 Mathematics Seminar  Prof. Hans Othmer (University of Minnesota) Analysis of models for direction sensing, actin waves, and surface
deformations in motile cells  abstractAbstractCell locomotion is essential for early
development, angiogenesis, tissue regeneration, the immune response, and wound
healing in multicellular organisms, and plays a very deleterious role in cancer
metastasis in humans. Locomotion involves the detection and transduction of
extracellular chemical and mechanical signals, integration of the signals into
an intracellular signal, and the spatiotemporal control of the intracellular
biochemical and mechanical responses that lead to force generation,
morphological changes and directed movement. In this talk we will discuss
mathematical models of direction sensing, how actin waves can be generated in
cells, and how a cell can propel itself via surface deformations.
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Mon 02/11/15 14:00 Fulton G20 Mathematics Seminar  Dr. Radostin Simitev (University of Glasgow) Convectiondriven dynamos in spherical shells and applications to the Solar Dynamo  abstractAbstractSimple selfconsistent models of magnetic field generation by convection in rotating spherical shells exhibit properties resembling those observed on the Sun. I will provide a review of some basic phenomenology of finiteamplitude convection and dynamo action in rotating spherical shells, including dependence on dimensionless parameters and dipolar dynamo bistability. I will then describe our recent efforts to apply these results to mimic properties of the Solar differential rotation, equatorialward migration of sunspots and active longitudes. I will also comment on the dynamo effects near the transition from Solar to antisolar differential rotation. hide 

Mon 09/11/15 14:00 Fulton G20 Mathematics Seminar  Prof. Jeremy Levesley (University of Leicester) Sparse grid approximation with Gaussians  abstractAbstractSparse grid approximation with polynomial splines has been a very successful method for approximation and solving PDEs. A downside to having to make a choice of degree of spline is that the convergence order is limited by this choice. We are developing sparse grid algorithms using radial basis functions, in particular the Gaussian. However, the Gaussian has the strange property that in a stationary scheme there is no convergence. So a multilevel method is required. We show numerically that this has good convergence properties. We will also present preliminary results that give convergence rates for multilevel quasiinterpolation. This result is the first multilevel result for smooth basis functions, and will open the door for sparse grid convergence estimates more generally (we hope!). hide 

Mon 16/11/15 14:00 Fulton G20 Mathematics Seminar  Prof. Hua Chen (Wuhan University) Estimates of Dirichlet Eigenvalues for Degenerate Elliptic Operators  abstractAbstractLet $\Omega$ be a bounded open domain in $R^n$ with smooth boundary and $X=(X_1, X_2, \cdots, X_m)$ be a system of
real smooth vector fields defined on $\Omega$ with the boundary $\partial\Omega$ which is noncharacteristic for $X$.
If $X$ satisfies the Hormander's condition, then the vector fields is finite degenerate and the sum of square operator
$\triangle_{X}=\sum_{j=1}^{m}X_j^2$ is a finitely degenerate elliptic operator, otherwise the operator $\triangle_{X}$ is
called infinitely degenerate. If $\lambda_j$ is the $j^{th}$ Dirichlet eigenvalue for $\triangle_{X}$ on $\Omega$, then
this paper shall study the lower bound estimates for $\lambda_j$. Firstly, by using the subelliptic estimate directly, we
shall give a simple lower bound estimates of $\lambda_j$ for general finitely degenerate $\triangle_{X}$ which is polynomial
increasing in $j$. Secondly, if $\triangle_{X}$ is socalled Grushin type degenerate elliptic operator, then we can give a precise
lower bound estimates for $\lambda_j$. Finally, by using logarithmic regularity estimate, for infinitely degenerate elliptic
operator $\triangle_{X}$ we prove that the lower bound estimates of $\lambda_j$ will be logarithmic increasing in $j$. hide 

Mon 23/11/15 14:00 Fulton G20 Mathematics Seminar  Dr. Nikos Kavallaris (University of Chester) On a nonlocal parabolic problem arising in game theory  abstractAbstractIn the current talk we first present the construction of a degenerate nonlocal equation which arises in the replicator dynamics system coming from the evolutionary game theory. Once the local existence is established we study the longtime behaviour of the preceding equation. Depending on the total mass of the initial data we either prove globaltime existence or finitetime blowup. For total mass equal to 1 then also the convergence towards the steadystates (Nash equilibria) is proven hide 

Mon 30/11/15 14:00 Fulton G20 Mathematics Seminar  Mr. Christopher Berg Smiet (University of Leiden) Hopf Fibrations and Field Lines  abstractAbstractThe Hopf map is a curious result in algebraic topology which was given in 1931 by Heinz Hopf. He showed a map between the hypershpere S^3 and the sphere S^2, in such a way that the fibers of the map (preimages of points on the sphere) are all circles that are all linked with one another. This was a breakthrough in topology, but in applied mathematics this result has lain dormant for many years. Recently there has been a revived interest in topological aspects of physical systems, and the topological structure the Hopf map has been applied to describe many physical systems. In this talk I will give a brief overview of the Hopf map, and how it can be applied as a versatile tool to construct new solutions of Maxwell's equations, describe a inherently selfstable plasma configuration, and be adapted to approximate the field of a relaxing helical plasma. hide 
