Forthcoming Seminars
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Tue, 18/10/2011 16:00 |
Professor Geoff Whittle (Victoria University of Wellington) |
Combinatorial Theory Seminar  |
L1 |
| A canonical way to obtain a matroid is from a finite set of vectors in a vector space over a field F. A matroid that can be obtained in such a way is said to be representable over F. It is clear that when Whitney first defined matroids he had matroids representable over the reals as his standard model, but for a variety of reasons most attention has focussed on matroids representable over finite fields. There is increasing evidence that the class of matroids representable over a fixed finite field is well behaved with strong general theorems holding. Essentially none of these theorems hold if F is infnite. Indeed matroids representable over the real– the natural matroids for our geometric intuition – turn out to be a mysterious class indeed. In the talk I will discuss this striking contrast in behaviour. | |||
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Tue, 18/10/2011 17:00 |
Algebra Seminar |
L2 | |
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Wed, 19/10/2011 10:10 |
Kevin Painter |
OCCAM Wednesday Morning Event |
OCCAM Common Room (RI2.28) |
| Successful navigation through a complicated and evolving environment is a fundamental task carried out by an enormous range of organisms, with migration paths staggering in their length and intricacy. Selecting a path requires the detection, processing and integration of a myriad of cues drawn from the surrounding environment and in many instances it is the intrinsic orientation of the environment that provides a valuable navigational aid. In this talk I will describe the use of transport models to describe migration in oriented environments, and demonstrate the scaling approaches that allow us to derive macroscopic models for movement. I will illustrate the methods through a number of apposite examples, including the migration of cells in the extracellular matrix, the macroscopic growth of brain tumours and the movement of wolves in boreal forest. | |||
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Wed, 19/10/2011 11:30 |
David Stewart |
Algebra Kinderseminar |
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Wed, 19/10/2011 16:00 |
Gareth Davies (University of Oxford) |
Analytic Topology in Mathematics and Computer Science |
L3 |
two-point sets|
Thu, 20/10/2011 11:00 |
Jamshid Derakhshan (Oxford) |
Advanced Class Logic |
SR2 |
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This is joint work with Uri Onn. We use motivic integration to get the growth rate of the sequence consisting of the number of conjugacy classes in quotients of G(O) by congruence subgroups, where $G$ is suitable algebraic group over the rationals and $O$ the ring of integers of a number field. The proof uses tools from the work of Nir Avni on representation growth of arithmetic groups and results of Cluckers and Loeser on motivic rationality and motivic specialization. |
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Thu, 20/10/2011 12:00 |
Tom Sutherland |
Junior Geometry and Topology Seminar |
SR2 |
We will describe the space of Bridgeland stability conditions
of the derived category of some CY3 algebras of quivers drawn on the
Riemann sphere. We give a biholomorphic map from the upper-half plane to
the space of stability conditions lifting the period map of a meromorphic
differential on a 1-dimensional family of elliptic curves. The map is
equivariant with respect to the actions of a subgroup of  on the
left by monodromy of the rational elliptic surface and on the right by
autoequivalences of the derived category.
The complement of a divisor in the rational elliptic surface can be
identified with Hitchin's moduli space of connections on the projective
line with prescribed poles of a certain order at marked points. This is
the space of initial conditions of one of the Painleve equations whose
solutions describe isomonodromic deformations of these connections. |
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Thu, 20/10/2011 12:30 |
Dmitry Beliaev (Oxford) |
OxPDE Lunchtime Seminar |
Gibson 1st Floor SR |
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Thu, 20/10/2011 13:00 |
Simon Cotter (OCCAM) |
Mathematical Finance Internal Seminar |
DH 1st floor SR |
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When modelling biochemical reactions within cells, it is
vitally important to take into account the effect of intrinsic noise in the
system, due to the small copy numbers of some of the chemical species.
Deterministic systems can give vastly different types of behaviour for the same
parameter sets of reaction rates as their stochastic analogues, giving us an
incorrect view of the bifurcation behaviour.
The stochastic description of this problem gives rise to a multi-dimensional Markov jump process, which can be approximated by a system of stochastic differential equations. Long-time behaviour of the process can be better understood by looking at the steady-state solution of the corresponding Fokker-Planck equation. In this talk we consider a new finite element method which uses simulated trajectories of the Markov-jump process to inform the choice of mesh in order to approximate this invariant distribution. The method has been implemented for systems in 3 dimensions, but we shall also consider systems of higher dimension. |
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Thu, 20/10/2011 14:00 |
Alessandro Sisto |
Junior Geometric Group Theory Seminar |
SR2 |
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Thu, 20/10/2011 14:00 |
Prof Hans Munthe-Kaas (University of Bergen) |
Computational Mathematics and Applications |
Gibson Grd floor SR |
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Thu, 20/10/2011 16:00 |
Alastair Rucklidge (University of Leeds) |
Differential Equations and Applications Seminar |
DH 1st floor SR |
| Three-wave interactions form the basis of our understanding of many nonlinear pattern forming systems because they encapsulate the most basic nonlinear interactions. In problems with two comparable length scales, such as the Faraday wave experiment with multi-frequency forcing, consideration of three-wave interactions can explain the presence of the spatio-temporal chaos found in some experiments, enabling some previously unexplained results to be interpreted in a new light. The predictions are illustrated with numerical simulations of a model partial differential equation. | |||
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Thu, 20/10/2011 16:00 |
Igor Wigman (Cardiff University) |
Number Theory Seminar |
L3 |
| Using the spectral multiplicities of the standard torus, weendow the Laplace eigenspaces with Gaussian probability measures.This induces a notion of random Gaussian eigenfunctionson the torus ("arithmetic random waves”.) We study thedistribution of the nodal length of random Laplace eigenfunctions for higheigenvalues,and our primary result is that the asymptotics for the variance isnon-universal, and is intimately related to the arithmetic oflattice points lying on a circle with radius corresponding to the energy. This work is joint with Manjunath Krishnapur and Par Kurlberg | |||
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Thu, 20/10/2011 17:00 |
Deborah Lockett (Leeds) |
Logic Seminar |
L3 |
| After a short introduction to homogeneous relational structures (structures such that all local symmetries are global), I will discuss some different topics relating homogeneity to homomorphisms: a family of notions of 'homomorphism-homogeneity' that generalise homogeneity; generic endomorphisms of homogeneous structures; and constraint satisfaction problems. | |||
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Fri, 21/10/2011 00:00 |
Mathematical Biology and Ecology Seminar |
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Fri, 21/10/2011 11:15 |
Ian Thompson (Department of Engineering Science, University of Oxford) |
Industrial and Interdisciplinary Workshops |
DH 1st floor SR |
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Fri, 21/10/2011 14:15 |
Luciano Campi (Paris 13) |
Nomura Seminar |
DH 1st floor SR |
| Abstract: In this paper we deal with a utility maximization problem at finite horizon on a continuous-time market with conical (and time varying) constraints (particularly suited to model a currency market with proportional transaction costs). In particular, we extend the results in \cite{CO} to the situation where the agent is initially endowed with a random and possibly unbounded quantity of assets. We start by studying some basic properties of the value function (which is now defined on a space of random variables), then we dualize the problem following some convex analysis techniques which have proven very useful in this field of research. We finally prove the existence of a solution to the dual and (under an additional boundedness assumption on the endowment) to the primal problem. The last section of the paper is devoted to an application of our results to utility indifference pricing. This is a joint work with G. Benedetti (CREST). | |||
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Fri, 21/10/2011 14:30 |
Prof. Carl Wunsch (MIT) |
Mathematical Geoscience Seminar |
DH 3rd floor SR |
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Studies of the ocean circulation and climate have come to be dominated by the results of complex numerical models encompassing hundreds of thousands of lines of computer code and whose physics may be more difficult to penetrate than the real system. Some insight into the large-scale ocean circulation can perhaps be gained by taking a step back and considering the gross time scales governing oceanic changes. These can derived from a wide variety of simple considerations such as energy flux rates, signal velocities, tracer equilibrium times, and others. At any given time, observed changes are likely a summation of shifts taking place over all of these time scales. |
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Mon, 24/10/2011 12:00 |
Michael Klaput (Oxford) |
String Theory Seminar |
L3 |
| String compactifications incorporating non-vanishing H-flux have received increased attention over the past decade for their potential relevance to the moduli stabilization problem. Their internal spaces are in general not Kähler and, therefore, not Calabi-Yau. In the heterotic string an important technical problem is to construct gauge bundles on such spaces. I will present a method of how to explicitly construct gauge bundles over homogeneous nearly-Kähler manifolds of dimension six and discuss some of the arising implications for model building. | |||
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Mon, 24/10/2011 14:15 |
Marta Sanz-Sole (Universitat de Barcelona) |
Stochastic Analysis Seminar |
Oxford-Man Institute |
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We consider nonlinear stochastic wave equations in dimension d\le 3. Using Malliavin Calculus, we give upper bounds for the small eigenvalues of the inverse of two point densities.These provide a rate of degeneracy when points go close to each other. Then, we analyze the consequences of this result on lower estimates for hitting probabilities. |
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