UBC

Mon 22 Oct 2018, 4:05pm
Algebraic Geometry Seminar
MATH 126

Bivariant Theories and Algebraic Cobordism of Singular Varieties

MATH 126
Mon 22 Oct 2018, 4:05pm5:05pm
Abstract
I will outline the construction of a natural bivariant theory extending algebraic bordism, which will yield an extension of algebraic cobordism to singular varieties. I will also discuss the connections of this theory to algebraic Ktheory and to intersection theory.
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Department of Mathematics, University of Waterloo

Tue 23 Oct 2018, 12:00pm
Scientific Computation and Applied & Industrial Mathematics
ESB 4133 (PIMS Lounge) Please note it starts 30 mins. earlier than the usual time.

Solving DNN Relaxations of the Quadratic Assignment Problem with ADMM and Facial Reduction

ESB 4133 (PIMS Lounge) Please note it starts 30 mins. earlier than the usual time.
Tue 23 Oct 2018, 12:00pm1:00pm
Abstract
The quadratic assignment problem, QAP, has many applications ranging from the planning of building locations of a university, to the positioning of modules on a computer chip (VLSI design), to the design of keyboards. This problem is arguably one of the hardest of the NPhard problems, as problems with dimension 30 are still considered hard to solve to optimality.
The QAP in the trace formulation is modelled as the minimization of a quadratic function over the permutation matrices. The set of permutation matrices can be represented by quadratic constraints. Relaxations of these constraints are used in branch and bound solution methods. These relaxations include the eigenvalue and projected eigenvalue relaxations, as well as various semidefinite programming, SDP, and doubly nonnegative, DNN, relaxations. These latter relaxations are particularly strong and often solve the QAP to optimality. However, they can be extremely expensive to solve.
We show that the combination of an alternating directions method of multipliers, ADMM, in combination with facial reduction works extremely well in solving the very difficult DNN relaxation.
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UBC

Tue 23 Oct 2018, 3:30pm
Diff. Geom, Math. Phys., PDE Seminar
MATH 105

Global NavierStokes flows for nondecaying initial data with slowly decaying oscillation

MATH 105
Tue 23 Oct 2018, 3:30pm4:30pm
Abstract
We consider the Cauchy problem of 3D incompressible NavierStokes equations for uniformly locally square integrable initial data. The existence of a timeglobal weak solution has been known, when the square integral of the initial datum on a ball vanishes as the ball goes to infinity. For nondecaying data, however, the only known global solutions are either for perturbations of constants or when the velocity gradients are in Lp with finite p. In this talk, I will outline how to construct global weak solutions for general nondecaying initial data whose local oscillations slowly decay.
This is a joint work with TaiPeng Tsai.
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UBC

Tue 23 Oct 2018, 4:00pm
Discrete Math Seminar
ESB 4127

The TriangleFree Process

ESB 4127
Tue 23 Oct 2018, 4:00pm5:00pm
Abstract
This is the first part of a two part exposition on the triangleprocess. The trianglefree process begins on an empty graph and adds edges at random, provided no triangle is created with the existing edges. One of the original motivations for the process came from Ramsey Theory. Spencer conjectured that the maximum size of an independent set in a graph resulting from the process should be relatively small, and so the trianglefree process would provide constructions for lower bounds on the Ramsey number R(3,t). Recently, Bohman and Keevash obtained new estimates on independence number of such graphs, which gives a lower bound on R(3,t) within a factor of 4+o(1) of the best know upper bound.
In this first part we will introduce random graph processes with an emphasis on the trianglefree process and the oddcyclefree process.
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Mathematics, SFU

Wed 24 Oct 2018, 3:00pm
Mathematical Biology Seminar
ESB 4127

Connecting genomic data with vaccine design through modelling

ESB 4127
Wed 24 Oct 2018, 3:00pm3:45pm
Abstract
While vaccines are available and are effective in protecting against colonisation and disease with Streptococcus pneumoniae, their effectiveness is limited by strain (serotype) replacement following widespread vaccination. Understanding the postvaccination balance of serotypes would present the opportunity to achieve a final population composed of the most benign (noninvasive) strains. However, the complex ecology of the pneumococcus makes it difficult to predict the postvaccination balance of strains. Recently, Corander et al proposed that there is widespread apparent negative frequencydependent selection (NFDS) in the pneumococcus (Corander et al 2017 Nat. Ecol. Evol.).
Here, we use this principle to develop a deterministic model of pneumococcal strain dynamics, and use the model to make predictions about the ecological response of the pneumococcal population to new candidate vaccine strategies. We find that we can identify formulations that outperform existing formulations in the model. Furthermore, it is possible to obtain a final model population that scores as well as the currently used formulation, using a vaccine strategy with fewer serotypes  these formulations would be much less costly to produce than current vaccines. We suggest that this approach could provide a template for principled vaccine design based on global surveillance data and genomics.
This is joint work with N. Croucher.
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Wed 24 Oct 2018, 4:00pm
Probability Seminar
ESB 2012

TBA

ESB 2012
Wed 24 Oct 2018, 4:00pm5:00pm
Abstract
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Seminar Information Pages

Note for Attendees
Sushi will be served.