Past SCAIM Seminars

Tue, 2017-06-13 12:30 - 14:00
Joshua Scurll, Department of Mathematics, The University of British Columbia
With super-resolution microscopy techniques such as Direct Stochastic Optical Reconstruction Microscopy (dSTORM), it is possible to image fluorescently labeled proteins on a cell membrane with high precision. Often, the extent to which such proteins cluster is biologically meaningful; for example, in B-cells, clustering of the B-cell receptor (BCR) is associated with increased intracellular signaling and B-cell activation, and spontaneous BCR clustering can cause chronic active BCR signaling that results in an aggressive B-cell malignancy.
Tue, 2017-05-30 12:30 - 14:00
Ailyn Stötzner, Faculty of Mathematics, TU Chemnitz
Elastoplastic deformations play a tremendous role in industrial forming. Many of these processes happen at non-isothermal conditions.Therefore, the optimization of such problems is of interest not only mathematically but also for applications. In this talk we will present the analysis of the existence of a global solution of an optimal control problem governed by a thermovisco(elasto)plastic model. We will point out the difficulties arising from the nonlinear coupling of the heat equation with the mechanical part of the model.
Tue, 2017-04-25 12:30 - 14:00
Paul Tupper, Mathematics, SFU
One important construction in the theory of metric spaces is the tight span. The tight span of a metric space can be thought of as a generalization of the idea of a convex hull in linear spaces and is the basis for much work in the study and visualization of finite metric spaces. Motivated by problems in phylogenetics, we have developed a generalization of the concept of metric spaces, which we call diversities. In a diversity, every subset of points in the space corresponds to a number, not just pairs, and there is a more general version of the triangle inequality.
Tue, 2017-04-04 12:30 - 14:00
Rongrong Wang, UBC Mathematics
In this talk, we examine two methods for frequency extrapolation. Frequency extrapolation is the problem of utilizing data processing techniques to obtain the entire spectrum of an objective signal while only a middle band is sampled. This problem is well-posed for signals with special structures, such as those with a few non-zeros. The study is motivated by seismic inversion. Due to physical constraints, data obtained from a seismic survey is severely limiting in both the low and high frequency extent for the purposes of inversion.
Tue, 2017-03-28 12:30 - 14:00
Marie Graff, Department of Earth, Ocean and Atmospheric Sciences, The University of British Columbia
A nonlinear optimization method is proposed for the solution of inverse scattering problems in the frequency domain, when the scattered field is governed by the Helmholtz equation. The time-harmonic inverse medium problem is formulated as a PDE-constrained optimization problem and solved by an inexact truncated Newton-type iteration. Instead of a grid-based discrete representation, the unknown wave speed is projected to a particular finite-dimensional basis of eigenfunctions, which is iteratively adapted during the optimization.
Tue, 2017-03-21 12:30 - 14:00
Curt Da Silva, Seismic Laboratory for Imaging and Modelling, The University of British Columbia
Many useful and interesting optimization problems can be cast in a convex composite form min_x h(c(x)), where h is a non-smooth but convex function and c is a smooth nonlinear or linear mapping. The non-smoothness of the outer function prevents traditional methods such as the Gauss-Newton method from converging quickly, which is problematic for large scale problems. In this talk, we will explore level set methods, aka the SPGL1 'trick', for solving this class of problem when we can easily project on to the level sets of h(z).
Tue, 2017-03-14 12:30 - 14:00
Iain Moyles, MACSI Limerick
Many chemical systems exhibit a regular pattern of precipitate bands known as Liesegang rings in tribute to the chemist Raphael E. Liesegang who demonstrated them using a reaction of silver nitrate and potassium dichromate. A variety of theories have been studied to try and understand how these patterns develop and one of the most seminal papers on the topic was a mathematical model developed by Keller and Rubinow using a supersaturation framework. This model predicted the formation of primary and secondary bands using heuristic arguments and assumptions about the underlying equations.
Tue, 2017-02-07 12:30 - 14:00
Chen Greif, Department of Computer Science, The University of British Columbia
We introduce SPMR, a new family of methods for iteratively solving saddle-point systems using a minimum or quasi-minimum residual approach. No symmetry assumptions are made. The basic mechanism underlying the method is a novel simultaneous bidiagonalization procedure that yields a simplified saddle-point matrix on a projected Krylov-like subspace, and allows for a monotonic short-recurrence iterative scheme. We develop a few variants, demonstrate the advantages of our approach, derive optimality conditions, and discuss connections to existing methods.
Tue, 2017-01-17 12:30 - 14:00
Ben Adcock, Department of Mathematics, Simon Fraser University
Many problems in scientific computing require the approximation of smooth, high-dimensional functions from limited amounts of data. For instance, a typical problem in uncertainty quantification involves identifying the parameter dependence of the output of a computational model.
Tue, 2017-01-10 12:30 - 14:00
Colin Macdonald, Department of Mathematics, The University of British Columbia
RIDC (revisionist integral deferred correction) methods are a class of time integrators well-suited to parallel computing. RIDC methods can achieve high-order accuracy in wall-clock time comparable to forward Euler. The methods use a predictor and multiple corrector steps. Each corrector is lagged by one time step; the predictor and each of the correctors can then be computed in parallel. This presentation introduces RIDC methods and demonstrates their effectiveness on some test problems.
Templates provided by UBC Department of Physics & Astronomy

a place of mind, The University of British Columbia

Faculty of Science
Institute of Applied Mathematics
311-6356 Agricultural Road
Vancouver, BC V6T 1Z2
Tel 604.822.8571
Fax 604.822.0957

Emergency Procedures | Accessibility | Contact UBC | © Copyright The University of British Columbia