Forthcoming Seminars
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Mon, 20/05 14:15 |
Ian Hambleton (McMaster/MPIM Bonn) |
Geometry and Analysis Seminar  |
L3 |
| The talk will survey some results about smooth and topological 4-manifolds obtained via surgery, and discuss some contrasting information provided by gauge theory about smooth finite group actions on 4-manifolds. | |||
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Mon, 20/05 14:15 |
CAMILLE MALE (ENS Lyon) |
Stochastic Analysis Seminar |
Oxford-Man Institute |
| Free probability theory has been introduced by Voiculescu in the 80's for the study of the von Neumann algebras of the free groups. It consists in an algebraic setting of non commutative probability, where one encodes "non commutative random variables" in abstract (non commutative) algebras endowed with linear forms (which satisfies properties in order to play the role of the expectation). In this context, Voiculescu introduce the notion of freeness which is the analogue of the classical independence. A decade later, he realized that a family of independent random matrices invariant in law by conjugation by unitary matrices are asymptotically free. This phenomenon is called asymptotic freeness. It had a deep impact in operator algebra and probability and has been generalized in many directions. A simple particular case of Voiculescu's theorem gives an estimate, for N large, of the spectrum of an N by N Hermitian matrix H_N = A_N + 1/\sqrt N X_N, where A_N is a given deterministic Hermitian matrix and X_N has independent gaussian standard sub-diagonal entries. Nevertheless, it turns out that asymptotic freeness does not hold in certain situations, e.g. when the entries of X_N as above have heavy-tails. To infer the spectrum of a larger class of matrices, we go further into Voiculescu's approach and introduce the distributions of traffics and their free product. This notion of distribution is richer than Voiculescu's notion of distribution of non commutative random variables and it generalizes the notion of law of a random graph. The notion of freeness for traffics is an intriguing mixing between the classical independence and Voiculescu's notion of freeness. We prove an asymptotic freeness theorem in that context for independent random matrices invariant in law by conjugation by permutation matrices. The purpose of this talk is to give an introductory presentation of these notions. | |||
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Mon, 20/05 15:45 |
Yang Su (Beijing) |
Topology Seminar |
L3 |
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In this talk I will introduce my joint work with Kreck on a classification of |
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Mon, 20/05 15:45 |
STEPHANE JAFFARD (universite PEC) |
Stochastic Analysis Seminar |
Oxford-Man Institute |
| Random wavelet series were introduced in the mid 90s as simple and flexible models that allow to take into account observed statistics of wavelet coefficients in signal and image processing. One of their most interesting properties is that they supply random processes whose pointwise regularity jumps form point to point in a very erratic way, thus supplying examples of multifractal processes. Interest in such models has been renewed recently under the spur of new applications coming from widely different fields; e.g. -in functional analysis, they allow to derive the regularity properties of “generic” functions in a given function space (in the sense of prevalence) -they offer toy examples on which one can check the accuracy of numerical algorithms that allow to derive the multifractal parameters associated with signals and images. We will give an overview of these properties, and we will focus on recent extensions whose sample paths are not locally bounded, and offer models for signals which share this property. | |||
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Mon, 20/05 16:00 |
Alastair Irving (Oxford) |
Junior Number Theory Seminar |
SR1 |
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Mon, 20/05 17:00 |
Bin Cheng (University of Surrey) |
Partial Differential Equations Seminar |
Gibson 1st Floor SR |
| This talk is regarding PDE systems from geophysical applications with multiple time scales, in which linear skew-self-adjoint operators of size 1/epsilon gives rise to highly oscillatory solutions. Analysis is performed in justifying the limiting dynamics as epsilon goes to zero; furthermore, the analysis yields estimates on the difference between the multiscale solution and the limiting solution. We will introduce a simple yet effective time-averaging technique which is especially useful in general domains where Fourier analysis is not applicable. | |||
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Tue, 21/05 12:00 |
Ivette Fuentes (Nottingham) |
Quantum Field Theory Seminar |
L3 |
| Cutting-edge experiments in quantum communications are reaching regimes where relativistic effects can no longer be neglected. For example, there are advanced plans to use satellites to implement teleportation and quantum cryptographic protocols. Relativistic effects can be expected at these regimes: the Global Positioning System (GPS), which is a system of satellites that is used for time dissemination and navigation, requires relativistic corrections to determine time and positions accurately. Therefore, it is timely to understand what are the effects of gravity and motion on entanglement and other quantum properties exploited in quantum information. In this talk I will show that entanglement can be created or degraded by gravity and non-uniform motion. While relativistic effects can degrade the efficiency of teleportation between moving observers, the effects can also be exploited in quantum information. I will show that the relativistic motion of a quantum system can be used to perform quantum gates. Our results, which will inform future space-based experiments, can be demonstrated in table-top experiments using superconducting circuits. | |||
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Tue, 21/05 14:00 |
Kevin McGerty (Oxford) |
Representation Theory Seminar |
L2 |
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Tue, 21/05 14:00 |
Kevin McGerty (Oxford) |
Algebraic and Symplectic Geometry Seminar |
L2 |
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Tue, 21/05 14:30 |
Paul Seymour (Princeton) |
Combinatorial Theory Seminar |
L3 |
| The “k-commodity flow problem” is: we are given k pairs of vertices of a graph, and we ask whether there are k flows in the graph, where the ith flow is between the ith pair of vertices, and has total value one, and for each edge, the sum of the absolute values of the flows along it is at most one. We may also require the flows to be 1/2-integral, or indeed 1/p-integral for some fixed p. If the problem is feasible (that is, the desired flows exist) then it is still feasible after contracting any edge, so let us say a flow problem is “critical” if it is infeasible, but becomes feasible when we contract any edge. In many special cases, all critical instances have only two vertices, but if we ask for integral flows (that is, p = 1, essentially the edge-disjoint paths problem), then there arbitrarily large critical instances, even with k = 2. But it turns out that p = 1 is the only bad case; if p>1 then all critical instances have bounded size (depending on k, but independent of p), and the same is true if there is no integrality requirement at all. The proof gives rise to a very simple algorithm for the k edge-disjoint paths problem in 4-edge-connected graphs. | |||
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Tue, 21/05 15:45 |
Tom Nevins (Illinois) |
Representation Theory Seminar |
L3 |
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Tue, 21/05 15:45 |
Tom Nevins (Illinois) |
Algebraic and Symplectic Geometry Seminar |
L3 |
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Tue, 21/05 17:00 |
Vladimir Troitsky (Alberta) |
Functional Analysis Seminar |
L3 |
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Tue, 21/05 17:00 |
Anreas Doering (Oxford) |
Algebra Seminar |
L2 |
| The spectral presheaf of a nonabelian von Neumann algebra or C*-algebra was introduced as a generalised phase space for a quantum system in the so-called topos approach to quantum theory. Here, it will be shown that the spectral presheaf has many features of a spectrum of a noncommutative operator algebra (and that it can be defined for other classes of algebras as well). The main idea is that the spectrum of a nonabelian algebra may not be a set, but a presheaf or sheaf over the base category of abelian subalgebras. In general, the spectral presheaf has no points, i.e., no global sections. I will show that there is a contravariant functor from unital C*-algebras to their spectral presheaves, and that a C*-algebra is determined up to Jordan *-isomorphisms by its spectral presheaf in many cases. Moreover, time evolution of a quantum system can be described in terms of flows on the spectral presheaf, and commutators show up in a natural way. I will indicate how combining the Jordan and Lie algebra structures may lead to a full reconstruction of nonabelian C*- or von Neumann algebra from its spectral presheaf. | |||
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Wed, 22/05 11:30 |
Levon Haykazyan |
Algebra Kinderseminar |
Queen's College |
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Thu, 23/05 12:00 |
Francesco Solombrino (Technical University of Munich) |
OxPDE Lunchtime Seminar |
Gibson 1st Floor SR |
| Inspired by some recents developments in the theory of small-strain elastoplasticity, we both revisit and generalize the formulation of the quasistatic evolutionary problem in perfect plasticity for heterogeneous materials recently given by Francfort and Giacomini. We show that their definition of the plastic dissipation measure is equivalent to an abstract one, where it is defined as the supremum of the dualities between the deviatoric parts of admissible stress fields and the plastic strains. By means of this abstract definition, a viscoplastic approximation and variational techniques from the theory of rate-independent processes give the existence of an evolution statisfying an energy- dissipation balance and consequently Hill's maximum plastic work principle for an abstract and very large class of yield conditions. | |||
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Thu, 23/05 12:00 |
Daniela Tonon (Imperial College & Institut de Mathématiques de Jussieu) |
OxPDE Lunchtime Seminar |
Gibson 1st Floor SR |
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Thu, 23/05 13:00 |
Mathematical Finance Internal Seminar |
DH 1st floor SR | |
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Thu, 23/05 14:00 |
Professor Gitta Kutyniok (TU Berlin) |
Computational Mathematics and Applications |
Gibson Grd floor SR |
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Thu, 23/05 15:00 |
TBA |
Junior Geometry and Topology Seminar |
SR1 |
