Past Seminars
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Mon, 11/02 12:00 |
David Marsh (Oxford) |
String Theory Seminar  |
L3 |
| I will describe recent efforts to understand the mediation of supersymmetry breaking in stabilized compactifications of type IIB string theory. By geometrically separating the visible sector from the supersymmetry breaking effects one may hope to achieve sequestered supersymmetry breaking and much ameliorated constraints from bounds on flavor changing neutral currents. However, in this talk I will discuss how non-perturbative superpotential cross-couplings between the visible sector and the Kähler moduli may spoil sequestering and introduce a sensitivity to the global details of the compactification. As a simple example, I will describe the structure of these `de-sequestering’ operators for a class of visible sectors realized by D-branes probing an orbifold singularity, and I will discuss their importance in the KKLT and LVS moduli stabilization scenarios. | |||
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Fri, 08/02 16:00 |
Dirk Becherer (Humboldt University) |
Nomura Seminar |
DH 1st floor SR |
| We discuss sparse portfolio optimization in continuous time. Optimization objective is to maximize an expected utility as in the classical Merton problem but with regularizing sparsity constraints. Such constraints aim for asset allocations that contain only few assets or that deviate only in few coordinates from a reference benchmark allocation. With a focus on growth optimization, we show empirical results for various portfolio selection strategies with and without sparsity constraints, investigating different portfolios of stock indicies, several performance measures and adaptive methods to select the regularization parameter. Sparse optimal portfolios are less sensitive to estimation errors and performance is superior to portfolios without sparsity constraints in reality, where estimation risk and model uncertainty must not be ignored. | |||
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Fri, 08/02 14:30 |
Dr Fenwick Cooper (AOPP University of Oxford) |
Mathematical Geoscience Seminar |
DH 3rd floor SR |
| We are interested in finding the Probability Density Function (PDF) of high dimensional chaotic systems such as a global atmospheric circulation model. The key difficulty stems from the so called “curse of dimensionality”. Representing anything numerically in a high dimensional space seems to be just too computationally expensive. Methods applied to dodge this problem include representing the PDF analytically or applying a (typically linear) transformation to a low dimensional space. For chaotic systems these approaches often seem extremely ad-hoc with the main motivation being that we don't know what else to do. The Lorenz 95 system is one of the simplest systems we could come up with that is both chaotic and high dimensional. So it seems like a good candidate for initial investigation. We look at two attempts to approximate the PDF of this system to an arbitrary level of accuracy, firstly using a simple Monte-Carlo method and secondly using the Fokker-Planck equation. We also describe some of the (sometimes surprising) difficulties encountered along the way. | |||
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Fri, 08/02 11:30 |
Various (OCCAM, University of Oxford) |
OCCAM Special Seminar |
OCCAM Common Room (RI2.28) |
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Fri, 08/02 09:45 |
Darren Kavanagh (Department of Engineering Science, University of Oxford) |
Industrial and Interdisciplinary Workshops |
DH 1st floor SR |
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Fri, 08/02 00:00 |
Mathematical Biology and Ecology Seminar |
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Thu, 07/02 17:00 |
Peter Holy (Bristol) |
Logic Seminar |
L3 |
| The Outer Model Programme investigates L-like forcing extensions of the universe, where we say that a model of Set Theory is L-like if it satisfies properties of Goedel's constructible universe of sets L. I will introduce the Outer Model Programme, talk about its history, motivations, recent results and applications. I will be presenting joint work with Sy Friedman and Philipp Luecke. | |||
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Thu, 07/02 16:00 |
Ian Hewitt (Oxford) |
Industrial and Applied Mathematics Seminar |
DH 1st floor SR |
| I discuss models for the planar spreading of a viscous fluid between an elastic lid and an underlying rigid plane. These have application to the growth of magmatic intrusions, as well as to other industrial and biological processes; simple experiments of an inflated blister will be used for motivation. The height of the fluid layer is described by a sixth order non-linear diffusion equation, analogous to the fourth order equation that describes surface tension driven spreading. The dynamics depend sensitively on the conditions at the contact line, where the sheet is lifted from the substrate and where some form of regularization must be applied to the model. I will explore solutions with a pre-wetted film or a constant-pressure fluid lag, for flat and inclined planes, and compare with the analogous surface tension problems. | |||
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Thu, 07/02 16:00 |
Kevin Buzzard (Imperial College London) |
Number Theory Seminar |
L3 |
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Toby Gee and I have proposed the definition of a "C-group", an extension of Langlands' notion of an L-group, and argue that for an arithmetic version of Langlands' philosophy such a notion is useful for controlling twists properly. I will give an introduction to this business, and some motivation. I'll start at the beginning by explaining what an L-group is a la Langlands, but if anyone is interested in doing some background preparation for the talk, they might want to find out for themselves what an L-group (a Langlands dual group) is e.g. by looking it up on Wikipedia! |
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Thu, 07/02 15:00 |
Jakob Blaavand |
Junior Geometry and Topology Seminar |
SR1 |
| This talk is a basic introduction to the wonderful world of Higgs bundles on a Riemann Surface, and their moduli space. We will only survey the basics of the theory focusing on the rich geometry of the moduli space of Higgs bundles, and the relation to moduli space of vector bundles. In the end we consider small applications of Higgs bundles. As this talk will be very basic we won't go into any new developments of the theory, but just mention the areas in which Higgs bundles are used today. | |||
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Thu, 07/02 14:00 |
Dr Winnifried Wollner (University of Hamburg) |
Computational Mathematics and Applications |
Gibson Grd floor SR |
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Subtitle:
And applications to problems involving pointwise constraints on the gradient of the state on non smooth polygonal domains
In this talk we are concerned with an analysis of Moreau-Yosida regularization of pointwise state constrained optimal control problems. As recent analysis has already revealed the convergence of the primal variables is dominated by the reduction of the feasibility violation in the maximum norm. We will use a new method to derive convergence of the feasibility violation in the maximum norm giving improved the known convergence rates. Finally we will employ these techniques to analyze optimal control problems governed by elliptic PDEs with pointwise constraints on the gradient of the state on non smooth polygonal domains. For these problems, standard analysis, fails because the control to state mapping does not yield sufficient regularity for the states to be continuously differentiable on the closure of the domain. Nonetheless, these problems are well posed. In particular, the results of the first part will be used to derive convergence rates for the primal variables of the regularized problem. |
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Thu, 07/02 13:00 |
Vladimir Cherny (Mathematics (Oxford)) |
Mathematical Finance Internal Seminar |
DH 1st floor SR |
| We consider a problem of maximising lifetime utility of consumption subject to a drawdown constraint on undiscounted wealth process. This problem was solved by Elie and Touzi in the case of zero interest rate. We apply methodology of Azema-Yor processes to connect constrained and unconstrained wealth processes, which allows us to get the results for non-zero interest rate. | |||
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Thu, 07/02 11:00 |
Kristian Strommen (Oxford) |
Advanced Logic Class |
SR1 |
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Wed, 06/02 17:00 |
Sylvia Serfaty (Universtité Paris 6 and Courant Institute) |
OxPDE Special Seminar |
Gibson 1st Floor SR |
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Wed, 06/02 16:00 |
Robin Knight (Oxford) |
Analytic Topology in Mathematics and Computer Science |
L3 |
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Wed, 06/02 16:00 |
Montserrat Casals-Ruiz (University of Oxford) |
Junior Geometric Group Theory Seminar |
SR2 |
| The theory of equations over groups goes back to the very beginning of group theory and is linked to many deep problems in mathematics, such as the Diophantine problem over rationals. In this talk, we shall survey some of the key results on equations over groups, give an outline of the Makanin-Razborov process (an algorithm for solving equations over free groups) and its connections to other results in group theory and low-dimensional topology. | |||
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Wed, 06/02 14:00 |
Scott Armstrong (Université Paris Dauphine) |
OxPDE Lunchtime Seminar |
Gibson Grd floor SR |
| We will present a regularity result for degenerate elliptic equations in nondivergence form. In joint work with Charlie Smart, we extend the regularity theory of Caffarelli to equations with possibly unbounded ellipticity– provided that the ellipticity satisfies an averaging condition. As an application we obtain a stochastic homogenization result for such equations (and a new estimate for the effective coefficients) as well as an invariance principle for random diffusions in random environments. The degenerate equations homogenize to uniformly elliptic equations, and we give an estimate of the ellipticity. | |||
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Wed, 06/02 10:30 |
Elisabeth Fink -- Queen's Lecture C |
Algebra Kinderseminar |
Queen's College |
| In the Greek mythology the hydra is a many-headed poisonous beast. When cutting one of its heads off, it will grow two more. Inspired by how Hercules defeated the hydra, Dison and Riley constructed a family of groups defined by two generators and one relator, which is an Engel word: the hydra groups. I will talk about its remarkably wild subgroup distortion and its hyperbolic cousin. Very recent discussions of Baumslag and Mikhailov show that those groups are residually torsion-free nilpotent and they introduce generalised hydra groups. | |||
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Wed, 06/02 10:15 |
Jacco Snoeijer (University of Twente) |
OCCAM Wednesday Morning Event |
OCCAM Common Room (RI2.28) |
When two drops come into contact they will rapidly merge and form a single drop. Here we address the coalescence of drops on a substrate, focussing on the initial dynamics just after contact. For very viscous drops we present similarity solutions for the bridge that connects the two drops, the size of which grows linearly with time. Both the dynamics and the self-similar bridge profiles are verified quantitatively by experiments. We then consider the coalescence of water drops, for which viscosity can be neglected and liquid inertia takes over. Once again, we find that experiments display a self-similar dynamics, but now the bridge size grows with a power-law  . We provide a scaling theory for this behavior, based on geometric arguments. The main result for both viscous and inertial drops is that the contact angle is important as it determines the geometry of coalescence – yet, the contact line dynamics appears irrelevant for the early stages of coalescence. |
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Tue, 05/02 17:00 |
Catalin Badea (Lille) |
Functional Analysis Seminar |
L3 |
