12:00
Invariant length scale in general relativity
Abstract
Dirac-Born-Infeld Kinematics
14:15
16:30
Symmetries in semidefinite programming, and how to exploit them
Abstract
Semidefinite programming (SDP) techniques have been extremely successful
in many practical engineering design questions. In several of these
applications, the problem structure is invariant under the action of
some symmetry group, and this property is naturally inherited by the
underlying optimization. A natural question, therefore, is how to
exploit this information for faster, better conditioned, and more
reliable algorithms. To this effect, we study the associative algebra
associated with a given SDP, and show the striking advantages of a
careful use of symmetries. The results are motivated and illustrated
through applications of SDP and sum of squares techniques from networked
control theory, analysis and design of Markov chains, and quantum
information theory.
12:00
17:00
Chemotactic Cell Movement and its Role in Development
Abstract
In St John's College.
Oxford Life Sciences Modelling Colloquia Series
12:00
17:00
Adaptive finite elements for relaxed methods (FERM) in computational microstructures
Abstract
15:45
A polling system with 3 queues and 1 server
is a.s. periodic when transient:
dynamical and stochastic systems, and a chaos
Abstract
We consider a queuing system with three queues (nodes) and one server.
The arrival and service rates at each node are such that the system overall
is overloaded, while no individual node is. The service discipline is the
following: once the server is at node j, it stays there until it serves all
customers in the queue.
After this, the server moves to the "more expensive" of the two
queues.
We will show that a.s. there will be a periodicity in the order of
services, as suggested by the behavior of the corresponding
dynamical systems; we also study the cases (of measure 0) when the
dynamical system is chaotic, and prove that then the stochastic one
cannot be periodic either.
15:30
A discontinuous Galerkin method for flow and transport in porous media
Abstract
Discontinuous Galerkin methods (DG) use trial and test functions that are continuous within
elements and discontinuous at element boundaries. Although DG methods have been invented
in the early 1970s they have become very popular only recently.
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DG methods are very attractive for flow and transport problems in porous media since they
can be used to solve hyperbolic as well as elliptic/parabolic problems, (potentially) offer
high-order convergence combined with local mass balance and can be applied to unstructured,
non-matching grids.
\\
In this talk we present a discontinuous Galerkin method based on the non-symmetric interior
penalty formulation introduced by Wheeler and Rivi\`{e}re for an elliptic equation coupled to
a nonlinear parabolic/hyperbolic equation. The equations cover models for groundwater flow and
solute transport as well as two-phase flow in porous media.
\\
We show that the method is comparable in efficiency with the mixed finite element method for
elliptic problems with discontinuous coefficients. In the case of two-phase flow the method
can outperform standard finite volume schemes by a factor of ten for a five-spot problem and
also for problems with dominating capillary pressure.
16:30