Mathematics Dept.
  Events
University of Tokyo
Mon 16 Sep 2019, 3:00pm
Algebraic Geometry Seminar
MATH 225
Birational geometry of the moduli spaces of coherent sheaves on blown-up surfaces
MATH 225
Mon 16 Sep 2019, 3:00pm-5:00pm

Abstract

To study the difference between motivic invariants of the moduli spaces of coherent sheaves on a smooth surface and that on the blown-up surface, Nakajima-Yoshioka constructed a sequence of flip-like diagrams connecting these moduli spaces. In this talk, I will explain birational geometric property of Nakajima-Yoshioka's wall crossing diagram. It turned out that it realizes a minimal model program.
hide
Ron M. Roth
Technion
Mon 16 Sep 2019, 4:00pm
Institute of Applied Mathematics
LSK 462
IAM-PIMS Distinguished Colloquium: Coding for Reliable Computing
LSK 462
Mon 16 Sep 2019, 4:00pm-5:00pm

Abstract

Coding theory has been associated mainly with maintaining reliability in communication and storage systems. Yet work published already in the 1950s by Von Neumann, Moore, and Shannon also considered the use of error handling techniques to maintain reliability of computation devices. Still, until very recently, the prevailing paradigm of designing computing devices appeared to put all of the effort of the reliability guarantee on the hardware design. Distributed computing, as well as the introduction of new nanoscale accelerator devices, are two examples of recent developments that have revived the interest in coding for reliable computation.

In this talk, we focus on accelerators that perform vector–matrix multiplication. We describe code designs that guarantee computation reliability under two paradigms: exact computation, which is needed when accelerating ordinary ALU computations, and approximate computation, which suits learning applications. In the latter, we view the computation to be over the real field, and introduce new tools for analyzing and synthesizing coding schemes for this model. In particular, we show connections between the code design problem and certain extremal problems of convex polygons

 

Note for Attendees

Reception at 3:30 in the IAM lounge (LSK 306).
hide
Lorena Aguirre Salazar
McMaster University
Tue 17 Sep 2019, 3:30pm
Diff. Geom, Math. Phys., PDE Seminar
Buchanan D307
On the TFDW model and the Ohta-Kawasaki model
Buchanan D307
Tue 17 Sep 2019, 3:30pm-4:30pm

Abstract

 The TFDW (Thomas-Fermi-Dirac-Weizacker) model has been used to describe certain electron configurations of molecules. On the other hand, the Ohta-Kawasaki model arises in the context of diblock copolymer melts. In this talk, we discuss results concerning compactness of minimizing sequences of the TFDW model and a variant of the Ohta-Kawasaki model.
hide
University of Washington
Tue 17 Sep 2019, 4:00pm
Discrete Math Seminar
ESB 4127
Resolving Stanley’s conjecture on k-fold acyclic complexes
ESB 4127
Tue 17 Sep 2019, 4:00pm-5:00pm

Abstract

In 1993, Stanley showed that if a simplicial complex is acyclic over some field, then its face poset can be decomposed into disjoint rank 1 boolean intervals whose minimal faces together form a subcomplex. Stanley further conjectured that complexes with a higher notion of acyclicity could be decomposed in a similar way using boolean intervals of higher rank. We provide an explicit counterexample to this conjecture. We also prove a special case of the conjecture, and show that a weaker decomposition into boolean trees always exists. This is joint work with Joseph Doolittle.
hide
Sarafa Iyaniwura
UBC Math
Wed 18 Sep 2019, 2:45pm
Mathematical Biology Seminar
ESB 4133 (PIMS Lounge)
Quorum Sensing and Synchronous Oscillations Triggered by Dynamically Active Signaling Compartments Coupled by Bulk Diffusion
ESB 4133 (PIMS Lounge)
Wed 18 Sep 2019, 2:45pm-3:45pm

Abstract

A coupled PDE-ODE model used to describe communication between dynamically active signaling compartments (biological cells) is analyzed using strong localized perturbation theory. In the limit D >> 1, the coupled model is reduced into a nonlinear system of ODEs, which is then used to study global coupling and synchronous oscillations among the cells. In addition, this reduced system is used to study quorum sensing and phase synchronization among the cells.
hide
UBC
Wed 18 Sep 2019, 2:45pm
Topology and related seminars
ESB 4127 (PIMS AV Room)
Configuration spaces of hard objects
ESB 4127 (PIMS AV Room)
Wed 18 Sep 2019, 2:45pm-3:45pm

Abstract

 Take n objects and put them in a container. What is the configuration space of all the ways they can fit in the container without intersecting? How does the topology of that configuration space change depending on the size of the objects and the size of the container? We will look at configurations of segments in a disk, of squares in a rectangle, and of disks in an infinite strip. In the latter two cases, the configuration space is homotopy equivalent to a polyhedral cell complex that can be studied combinatorially.

Note for Attendees

 The Topology seminar has been moved to ESB 4127 (the Math Bio seminar is now in ESB 4133)
hide
U. Bath
Wed 18 Sep 2019, 3:00pm
Probability Seminar
ESB 1012
Branching Brownian motion with selection and a free boundary problem
ESB 1012
Wed 18 Sep 2019, 3:00pm-4:00pm

Abstract

Consider a system of N particles moving according to Brownian motions and branching at rate one. Each time a particle branches, the particle in the system furthest from the origin is killed. It turns out that we can use results about a related partial differential equation known as a free boundary problem to control the long term behavior of this particle system for large N. This is joint work with Julien Berestycki, Eric Brunet and James Nolen.

hide
U. Bath
Fri 20 Sep 2019, 3:00pm
Department Colloquium
ESB 1012
Rising Stars Colloquium - The motion of hybrid zones and genealogies in pushed waves
ESB 1012
Fri 20 Sep 2019, 3:00pm-4:00pm

Abstract

Suppose two populations with different genetic types live close to each other and can interbreed, but hybrid offspring have a lower evolutionary fitness. The interface between such populations is known as a hybrid zone. We can model this situation using a stochastic process. I will discuss a result on the motion of the interface, which is related to a well-known PDE result connecting the Allen-Cahn equation and mean curvature flow.

If we take a simplified model in only one spatial dimension, we can trace the ancestral lineages of individuals backwards in time and (in some cases) determine the asymptotic behavior of the genealogy (or family tree) of a set of individuals. Several interesting questions about the genealogies remain open.

Partly based on joint work with Alison Etheridge and Nic Freeman.

Note for Attendees

Refreshments will be served at 2:30 p.m. in ESB 4133 (Lounge).
hide