Forthcoming Seminars
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Mon, 26/10/2009 15:45 |
Alan Hammond (New York University) |
Stochastic Analysis Seminar  |
Eagle House |
| Condition supercritical percolation so that the origin is enclosed by a dual circuit whose interior traps an area of n^2. The Wulff problem concerns the shape of the circuit. We study the circuit's fluctuation. A well-known measure of this fluctuation is maximum local roughness (MLR), which is the greatest distance from a point on the circuit to the boundary of circuit's convex hull. Another is maximum facet length (MFL), the length of the longest line segment of which this convex hull is comprised. In a forthcoming article, I will prove that for various models including supercritical percolation, under the conditioned measure, MLR = \Theta(n^{1/3}\log n)^{2/3}) and MFL = \Theta(n^{2/3}(log n)^{1/3}). An important tool is a result establishing the profusion of regeneration sites in the circuit boundary. The talk will focus on deriving the main results with this tool | |||
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Mon, 26/10/2009 16:00 |
Jahan Zahid (Mathematical Institute, Oxford) |
Junior Number Theory Seminar |
SR1 |
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Mon, 26/10/2009 17:00 |
Juan Velasquez (Universidad Complutense Madrid) |
Partial Differential Equations Seminar |
Gibson 1st Floor SR |
| In this talk I will present the rigorous construction of singular solutions for two kinetic models, namely, the Uehling-Uhlenbeck equation (also known as the quantum Boltzmann equation), and a class of homogeneous coagulation equations. The solutions obtained behave as power laws in some regions of the space of variables characterizing the particles. These solutions can be interpreted as describing particle fluxes towards or some regions from this space of variables. The construction of the solutions is made by means of a perturbative argument with respect to the linear problem. A key point in this construction is the analysis of the fundamental solution of a linearized problem that can be made by means of Wiener-Hopf transformation methods. | |||
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Tue, 27/10/2009 12:00 |
Simon Brain (SISSA) |
Quantum Field Theory Seminar |
L3 |
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Tue, 27/10/2009 14:15 |
Prof. Peter Davidson (University of Cambridge) |
Geophysical and Nonlinear Fluid Dynamics Seminar |
Dobson Room, AOPP |
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Tue, 27/10/2009 14:30 |
Stanislav Volkov (Bristol) |
Combinatorial Theory Seminar |
L3 |
The simple harmonic urn is a discrete-time stochastic process on  approximating the phase portrait of the harmonic oscillator using very basic transitional probabilities on the lattice, incidentally related to the Eulerian numbers.
This urn which we consider can be viewed as a two-colour generalized Polya urn with negative-positive reinforcements, and in a sense it can be viewed as a “marriage” between the Friedman urn and the OK Corral model, where we restart the process each time it hits the horizontal axes by switching the colours of the balls. We show the transience of the process using various couplings with birth and death processes and renewal processes. It turns out that the simple harmonic urn is just barely transient, as a minor modification of the model makes it recurrent.
We also show links between this model and oriented percolation, as well as some other interesting processes.
This is joint work with E. Crane, N. Georgiou, R. Waters and A. Wade. |
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Tue, 27/10/2009 17:00 |
Pedro Miana (Zaragoza) |
Functional Analysis Seminar |
L3 |
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Tue, 27/10/2009 17:00 |
Michael Wemyss (Oxford) |
Algebra Seminar |
L2 |
| I'll explain how the `Auslander philosophy' from finite dimensional algebras gives new methods to tackle problems in higher-dimensional birational geometry. The geometry tells us what we want to be true in the algebra and conversely the algebra gives us methods of establishing derived equivalences (and other phenomenon) in geometry. Algebraically two of the main consequences are a version of AR duality that covers non-isolated singularities and also a theory of mutation which applies to quivers that have both loops and two-cycles. | |||
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Wed, 28/10/2009 10:10 |
Andrew Davidson |
OCCAM Literature Seminar |
OCCAM Common Room (RI2.28) |
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Wed, 28/10/2009 11:30 |
Owen Cotton-Barratt (University of Oxford) |
Algebra Kinderseminar |
ChCh, Tom Gate, Room 2 |
| Much of group theory is concerned with whether one property entails another. When such a question is answered in the negative it is often via a pathological example. We will examine the Rips construction, an important tool for producing such pathologies, and touch upon a recent refinement of the construction and some applications. In the course of this we will introduce and consider the profinite topology on a group, various separability conditions, and decidability questions in groups. | |||
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Thu, 29/10/2009 11:00 |
Martin Bays (Oxford) |
Advanced Logic Class |
SR2 |
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Thu, 29/10/2009 11:00 |
Dr Jara Imbers (Oxford) |
Applied Dynamical Systems and Inverse Problems Seminar |
DH 3rd floor SR |
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Thu, 29/10/2009 12:00 |
George Raptis (Oxford) |
Junior Geometry and Topology Seminar |
SR1 |
| The talk is about the homotopy type of configuration spaces. Once upon a time there was a conjecture that it is a homotopy invariant of closed manifolds. I will discuss the strong evidence supporting this claim, together with its recent disproof by a counterexample. Then I will talk about the corrected version of the original conjecture. | |||
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Thu, 29/10/2009 13:00 |
Xuoquan Xu (MCFG) |
Mathematical Finance Internal Seminar |
DH 1st floor SR |
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Thu, 29/10/2009 14:00 |
Dr. Wayne Hayes (UC Irvine and Imperial College London) |
Computational Mathematics and Applications |
3WS SR |
| The stability of our Solar System has been debated since Newton devised the laws of gravitation to explain planetary motion. Newton himself doubted the long-term stability of the Solar System, and the question has remained unanswered despite centuries of intense study by generations of illustrious names such as Laplace, Langrange, Gauss, and Poincare. Finally, in the 1990s, with the advent of computers fast enough to accurately integrate the equations of motion of the planets for billions of years, the question has finally been settled: for the next 5 billion years, and barring interlopers, the shapes of the planetary orbits will remain roughly as they are now. This is called "practical stability": none of the known planets will collide with each other, fall into the Sun, or be ejected from the Solar System, for the next 5 billion years. Although the Solar System is now known to be practically stable, it may still be "chaotic". This means that we may—or may not—be able precisely to predict the positions of the planets within their orbits, for the next 5 billion years. The precise positions of the planets effects the tilt of each planet's axis, and so can have a measurable effect on the Earth's climate. Although the inner Solar System is almost certainly chaotic, for the past 15 years, there has been some debate about whether the outer Solar System exhibits chaos or not. In particular, when performing numerical integrations of the orbits of the outer planets, some astronomers observe chaos, and some do not. This is particularly disturbing since it is known that inaccurate integration can inject chaos into a numerical solution whose exact solution is known to be stable. In this talk I will demonstrate how I closed that 15-year debate on chaos in the outer solar system by performing the most carefully justified high precision integrations of the orbits of the outer planets that has yet been done. The answer surprised even the astronomical community, and was published in _Nature Physics_. I will also show lots of pretty pictures demonstrating the fractal nature of the boundary between chaos and regularity in the outer Solar System. | |||
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Thu, 29/10/2009 14:30 |
John Murray (Maynooth (Ireland)) |
Representation Theory Seminar |
L3 |
| (Joint with Harald Ellers, Allegheny College, PA, USA) Carter and Payne constructed homomorphisms between Specht modules for the symmetric groups, based on moving boxes of the same residue in the associated partition diagrams. We study the special case of a one-box-shift. In particular, we give a lower bound for the Jantzen submodule of the codomain that contains the image. | |||
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Thu, 29/10/2009 16:00 |
Martin Bright (Warwick) |
Number Theory Seminar |
L3 |
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Thu, 29/10/2009 16:30 |
Steve Fitzgerald (EURATOM/UKAEA Fusion Association (Oxford)) |
Differential Equations and Applications Seminar |
DH 1st floor SR |
| Frank-Read sources are among the most important mechanisms of dislocation multiplication, and their operation signals the onset of yield in crystals. We show that the critical stress required to initiate dislocation production falls dramatically at high elastic anisotropy, irrespective of the mean shear modulus. We hence predict the yield stress of crystals to fall dramatically as their anisotropy increases. This behaviour is consistent with the severe plastic softening observed in alpha-iron and ferritic steels as the alpha − gamma martensitic phase transition is approached, a temperature regime of crucial importance for structural steels designed for future nuclear applications. | |||
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Thu, 29/10/2009 17:00 |
Deirdre Haskell (Mcmaster) |
Logic Seminar |
L3 |
| VC dimension and density are properties of a collection of sets which come from probability theory. It was observed by Laskowski that there is a close tie between these notions and the model-theoretic property called NIP. This tie results in many examples of collections of sets that have finite VC dimension. In general, it is difficult to find upper bounds for the VC dimension, and known bounds are mostly very large. However, the VC density seems to be more accessible. In this talk, I will explain all of the above acronyms, and present a theorem which gives an upper bound (in some cases optimal) on the VC density of formulae in some examples of NIP theories. This represents joint work of myself with M. Aschenbrenner, A. Dolich, D. Macpherson and S. Starchenko. | |||
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Fri, 30/10/2009 10:00 |
Doug Watson (Thales UK) |
Industrial and Interdisciplinary Workshops |
DH 1st floor SR |
