Past

We consider Markovian models on graphs with local dynamics. We show that, under suitable conditions, such Markov chains exhibit both rapid convergence to equilibrium and strong concentration of measure in the stationary distribution. We illustrate our results with applications to some known chains from computer science and statistical mechanics.

This talk will mention methods of testing whether a given integer is prime. Included topics are Carmichael numbers, Fermat and Euler pseudo-primes and results contingent on the Generalised Riemann Hypothesis.

The notion of a sutured 3-manifold was introduced by Gabai. It is a powerful tool in 3-dimensional topology. A few years ago, Andras Juhasz defined an invariant of sutured manifolds called sutured Floer homology.

I'll discuss a simpler invariant obtained by taking the Euler characteristic of this theory. This invariant turns out to have many properties in common with the Alexander polynomial. Joint work with Stefan Friedl and Andras Juhasz.

This talk is based on a joint work with Zhan Shi: We establish a second-order almost sure limit theorem for the minimal position in a one-dimensional super-critical branching random walk, and also prove a martingale convergence theorem which answers a question of Biggins and Kyprianou (2005). Our method applies furthermore to the study of directed polymers on a disordered tree. In particular, we give a rigorous proof of a phase transition phenomenon for the partition function (from the point of view of convergence in probability), already described by Derrida and Spohn (1988). Surprisingly, this phase transition phenomenon disappears in the sense of upper almost sure limits.

Let $\mathbb{E}$ be an elliptic curve defined over a number field $k$,

and let $a\in\mathbb{E}(\mathbb{C})$ be a complex point. Among the

possible choices of sequences of division points of $a$, $(a_n)_n$

such that $a_1 = a$ and $na_{nm} = a_m$, we can pick out those which

converge in the complex topology to the identity. We show that the

algebraic content of this effect of the complex topology is very

small, in the sense that any set of division sequences which shares

certain obvious algebraic properties with the set of those which

converge to the identity is conjugated to it by a field automorphism

of $\mathbb{C}$ over $k$.

As stated, this is a result of algebra and number theory. However, in

proving it we are led ineluctably to use model theoretic techniques -

specifically the concept of "excellence" introduced by Shelah for the

analysis of $L_{\omega_1,\omega}$ categoricity, which reduces the

question to that of proving certain unusual versions of the theorems

of Mordell-Weil and Kummer-Bashmakov. I will discuss this and other

aspects of the proof, without assuming any model- or number-theoretic

knowledge on the part of my audience.

We develop several results on hitting probabilities of random fields which highlight the role of the dimension of the parameter space. This yields upper and lower bounds in terms of Hausdorff measure and Bessel-Riesz capacity, respectively. We apply these results to a system of stochastic wave equations in spatial dimension k≥1 driven by a d-dimensional spatially homogeneous additive Gaussian noise that is white in time and coloured in space.

Brownian Molecular Motors are crucial for cell motility, muscle contraction or any other mechanical task carried out by proteins. After a short introduction to protein motors, I will talk about a numerical appraoch I worked on during the last months, which should enable us to deduct properties for a broad range of protein motors. A special focus should lie on the calculation of the eigenvalue spectrum, which gives insight to motors' stability.

My talk will be about optimal investment in Kabanov's model of currency exchange with transaction costs. The model is general enough to allow a random, discontinuous bid-offer spread. The investor wishes to maximize their "direct" utility of consumption, which is measured in terms of consumption assets linked to some (but not necessarily all) of the traded currencies. The analysis will centre on two conditions under which the existence of a dual minimiser leads to the existence of an optimal terminal wealth. The first condition is a well known, but rather unintuitive, condition on the utility function. The second weaker, and more natural condition is that of "asymptotic satiability" of the value function. We show that the portfolio optimization problem can be reformulated in terms of maximization of a terminal liquidation utility function, and that both problems have a common optimizer. This is joint work with Luciano Campi.

About a third of us will have a cancer during our lives, and we all know someone with the disease. Despite enormous progress in recent years, so that being diagnosed with cancer is not the death sentence that it once was, treatment can be aggressive, leading to short and long term reductions in quality of life. Cancer and its treatment is still feared, and rightly so - it is a major health concern. Destroying cancer non-invasively using protons or charged light ions such as carbon (Particle Therapy Cancer Research or PTCR) offers advantages over conventional radiotherapy using x-rays, since far lower radiation dose is delivered to healthy normal tissues. PT is also an alternative to radical cancer surgery. Most radiotherapy uses a small electron linear accelerator to accelerate an electron beams to a few million volts and then to generate hard x-rays, whereas CPT uses cyclotrons or synchrotrons to accelerate protons to a few hundred million volts, which themselves sterilise the tumour. More recently, a new concept in accelerators – the “non-scaling Fixed Field Alternating Gradient” accelerator – has been advanced, which offers the prospect of developing relatively compact, high acceleration rate accelerators for a variety of purposes, from neutrino factories and muon acceleration to cancer therapy. However, there are formidable technical challenges to be overcome, including resonance crossing. We have recently been awarded funding in the UK to construct a demonstrator non-scaling FFAG at the Daresbury laboratory (EMMA, the Electron Model with Many Applications), and to design a prototype machine for proton and carbon ion cancer therapy (PAMELA, the Particle Accelerator for MEdicaL Applications). I will describe some of the motivations for developing this new type of accelerator. Finally, although the physics of CPT says that it should be qualitatively and quantitatively better than conventional radiotherapy, the robust clinical analyses (for example, randomised control trials) have not been done, and the meta-analyses seem to suffer from large sample biases. The Particle Therapy Cancer Research Institute (part of the James Martin 21st Century School in Oxford) will study the clinical effectiveness of charged particle therapy to treat cancer, promoting its use in the UK and elsewhere on the basis of robust clinical evidence and analysis.

I will provide an overview of theoretical models aimed at understanding how self-excited oscillations arise when flow is driven through a finite-length flexible tube or channel. This problem is approached using a hierarchy of models, from one to three spatial dimensions, combining both computational and asymptotic techniques. I will explain how recent work is starting to shed light on the relationship between local and global instabilities, energy balances and the role of intrinsic hydrodynamic instabilities. This is collaborative work with Peter Stewart, Robert Whittaker, Jonathan Boyle, Matthias Heil and Sarah Waters.

We are interested in optimizing the compliance of an elastic structure when the applied forces are partially unknown or submitted to perturbations, the so-called "robust compliance".

For linear elasticity,the compliance is a solution to a minimizing problem of the energy. The robust compliance is then a min-max, the minimum beeing taken amongst the possible displacements and the maximum amongst the perturbations. We show that this problem is well-posed and easy to compute.

We then show that the problem is relatively easy to differentiate with respect to the domain and to compute the steepest direction of descent.

The levelset algorithm is then applied and many examples will explain the different mathematical and technical difficulties one faces when one

tries to tackle this problem.