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.
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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).
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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.
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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.
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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.
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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)
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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.

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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).
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Ming Zhang
UBC
Mon 23 Sep 2019, 3:00pm
Algebraic Geometry Seminar
MATH 225
TBA
MATH 225
Mon 23 Sep 2019, 3:00pm-5:00pm

Abstract

 TBA
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UBC
Tue 24 Sep 2019, 3:30pm
Diff. Geom, Math. Phys., PDE Seminar
Buchanan D307
Eigenfunction decay rates for eigenvalues at threshold of essential spectrum
Buchanan D307
Tue 24 Sep 2019, 3:30pm-4:30pm

Abstract

 In the talk we present a new method for calculating decay rates of eigenfunctions for eigenvalues below the threshold of the essential spectrum. The method is also applicable for eigenvalues at the threshold provided that the eigenfunction exists. In fact, our a-priori bounds are the crucial first step for the proof that bound states at the thresholds exist. We consider the example of a helium atom and show that the decay rate of an eigenfunction at the threshold of the essential spectrum behaves as exp(− C􏰂|x|∞ ), where |x|∞ = max(|x|) is the maximum of electron coordinates. Moreover we show a similar result for the Froehlich Bipolaron.
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UBC
Tue 24 Sep 2019, 4:00pm
Discrete Math Seminar
ESB 4127
Normal lattice supercharacter theories and Hopf structures
ESB 4127
Tue 24 Sep 2019, 4:00pm-5:00pm

Abstract

The concept of Hopf algebras originated from the theory of algebraic groups and algebraic topology in the mid 20th century. Hopf structures have numerous applications in many other mathematical branches, and now it is a familiar concept in representation theory as the class functions and superclass functions of some tower of groups have Hopf structures. In these Hopf structures, representation theoretic functors give the product and coproduct. In this talk, we give a brief introduction to normal lattice supercharacter theories, and then we construct a Hopf structure by using these supercharacter theories.
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U. Chicago
Wed 25 Sep 2019, 3:00pm
Probability Seminar
ESB 1012
Multiple SLE from a Loop Measure Perspective
ESB 1012
Wed 25 Sep 2019, 3:00pm-4:00pm

Abstract

I will discuss the role of Brownian loop measure in the study of

Schramm-Loewner evolution. This powerful perspective allows us to apply

intuition from discrete models (in particular, the λ-SAW model) to the study of

SLE while simultaneously reducing many SLE computations to problems of

stochastic calculus. I will discuss recent work on multiple radial SLE that

employs this method, including the construction of global multiple radial SLE

and its links to locally independent SLE and Dyson Brownian motion. (Joint work

with Gregory F. Lawler.)

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UC Riverside
Mon 30 Sep 2019, 3:30pm SPECIAL
Diff. Geom, Math. Phys., PDE Seminar
MATH 202
The Sphere Covering Inequality and Its Applications
MATH 202
Mon 30 Sep 2019, 3:30pm-4:30pm

Abstract

I will talk about a new geometric inequality: the Sphere Covering Inequality. The inequality states that the total area of two distinct surfaces with Gaussian curvature less than 1, which are also conformal to the Euclidean unit disk with the same conformal factor on the boundary, must be at least 4π. In other words, the areas of these surfaces must cover the whole unit sphere after a proper rearrangement. We apply the Sphere Covering Inequality to solve several open problems about uniqueness and symmetry of solutions of mean field type equations. In particular we apply this inequality to prove an old conjecture of A. Chang and P. Yang about the best constant of a Moser-Trudinger type inequality. 
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École Polytechnique Paris
Mon 30 Sep 2019, 4:00pm
Algebraic Geometry Seminar
MATH 225
Degree growth of rational maps
MATH 225
Mon 30 Sep 2019, 4:00pm-5:00pm

Abstract

The understanding of the growth of degrees of iterates of a rational self-map of a projective variety is a fundamental problem in holomorphic dynamics. I shall review some basic results of the theory and discuss some recent directions of research. 
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Nick Olson-Harris
U. Waterloo
Tue 1 Oct 2019, 4:00pm
Discrete Math Seminar
ESB 4127
TBA
ESB 4127
Tue 1 Oct 2019, 4:00pm-5:00pm

Abstract


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David Holloway
BCIT
Wed 2 Oct 2019, 2:45pm
Mathematical Biology Seminar
ESB 4133
Leaf vein patterning: growth regulator dynamics of normal and transport-disrupted development
ESB 4133
Wed 2 Oct 2019, 2:45pm-3:45pm

Abstract

The growth regulator auxin plays a central role in development across plants. Auxin spatial patterning is critical in the phyllotactic arrangement of leaves along a stem, the shapes of the leaves themselves, and venation within leaves. These patterns depend on polar auxin transport (PAT) at the cellular level, particularly the preferential allocation of PIN efflux proteins to certain areas of the plasma membrane. Two general mechanisms have been studied: an up-the-gradient (UTG) allocation dependent on neighbouring-cell auxin concentrations, and a with-the-flux (WTF) allocation dependent on the flow of auxin across walls. We developed a combined UTG+WTF model for leaf venation. The model simulates intracellular and membrane kinetics and intercellular transport, and is solved for a 2D leaf of several hundred cells. We find that vein initiation in the leaf margin and cell polarization towards new veins is UTG-driven, while WTF is critical for vein extension. UTG is important for joining veins to form a network structure. The model produces the experimentally observed succession of effects when PAT is increasingly inhibited by NPA treatment. Venation patterns are highly correlated with leaf shape; this model enables the investigation of how PAT dynamics contribute to the diversity of leaf shapes across plants.
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UBC Physics
Wed 2 Oct 2019, 2:45pm
ESB 4127
TBA
ESB 4127
Wed 2 Oct 2019, 2:45pm-3:45pm

Details

 TBA
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UBC Math
Fri 4 Oct 2019, 3:00pm
Department Colloquium
ESB 1012
TBA
ESB 1012
Fri 4 Oct 2019, 3:00pm-4:00pm

Abstract


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Jongchon Kim
UBC
Mon 7 Oct 2019, 11:05am
Harmonic Analysis Seminar
MATH 126
L^2 bounds for a maximal directional Hilbert transform
MATH 126
Mon 7 Oct 2019, 11:05am-10:00am

Abstract

Given a direction set in Euclidean space, we consider a maximal function for the directional Hilbert transforms associated with the direction set.  For each finite p>1, it is known that this maximal function is bounded on L^p if and only if the direction set is finite. This raises the following quantitative problems; 
1) What is a sharp uniform upper bound on the L^p-operator norm of the maximal function that depends only on the cardinality of direction sets? 
2) Under which geometric assumptions on direction sets can this uniform bound be improved? 
We will study these problems for the p=2 case using polynomial partitioning tools from discrete geometry and an almost-orthogonality principle for the maximal function. This is a joint work with Malabika Pramanik.
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McGill University
Mon 7 Oct 2019, 3:00pm
Department Colloquium
TBD
TBD
TBD
Mon 7 Oct 2019, 3:00pm-4:00pm
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Rutgers University
Mon 7 Oct 2019, 4:00pm
Algebraic Geometry Seminar
MATH 225
TBA
MATH 225
Mon 7 Oct 2019, 4:00pm-5:00pm

Abstract


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Zhichao Wang
MPIM Bonn
Tue 8 Oct 2019, 3:30pm
Diff. Geom, Math. Phys., PDE Seminar
Buchanan D307
Recent developments of free boundary minimal hypersurfaces
Buchanan D307
Tue 8 Oct 2019, 3:30pm-4:30pm

Abstract

In this talk, I will introduce some recent developments of free boundary minimal hypersurfaces, including compactness, generic finiteness and index estimates. As an application, we also give the existence of infinitely many minimal hypersurfaces with non-empty free boundary under some weak assumptions. Part of the work is joint with Q.Guang, M.Li and X.Zhou
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Chris Ryan
Sauder, UBC
Tue 8 Oct 2019, 4:00pm
Discrete Math Seminar
ESB 4127
The discrete moment problem with nonconvex shape constraints
ESB 4127
Tue 8 Oct 2019, 4:00pm-5:00pm

Abstract

The discrete moment problem is a foundational problem in distribution-free robust optimization, where the goal is to find a worst-case distribution that satisfies a given set of moments. This paper studies the discrete moment problems with additional “shape constraints” that guarantee the worst-case distribution is either log-concave (LC), has an increasing failure rate (IFR), or an increasing generalized failure rate (IGFR). These classes of shape constraints have not previously been studied in the literature, in part due to their inherent nonconvexities. Nonetheless, these classes of distributions are useful in practice with applications in revenue management, reliability, and inventory control. We characterize the structure of optimal extreme point distributions. We show, for example, that an optimal extreme point solution to a moment problem with m moments and LC shape constraints is piecewise geometric with at most m pieces. 

This is joint work with Xi Chen (NYU, Stern School of Business), Simai He (Shanghai University of Finance and Economics, School of Information Management and Engineering), Bo Jiang (Shanghai University of Finance and Economics, School of Information Management and Engineering), and Teng Zhang (Stanford, Management Science and Engineering).
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Cornell University
Wed 16 Oct 2019, 4:00pm
Probability Seminar
TBA
Wed 16 Oct 2019, 4:00pm-5:00pm

Abstract

 
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Cornell University
Fri 18 Oct 2019, 3:00pm
Department Colloquium
ESB 1012
(PIMS/UBC distinguished colloquium) TBA
ESB 1012
Fri 18 Oct 2019, 3:00pm-4:00pm

Abstract

 

Note for Attendees

Refreshments will be served at 2:30 p.m. in ESB 4133 (Lounge).
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UBC
Mon 21 Oct 2019, 3:00pm
Algebraic Geometry Seminar
MATH 225
TBA
MATH 225
Mon 21 Oct 2019, 3:00pm-5:00pm

Abstract

 TBA
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Kevin O'Neill
University of California, Berkeley
Tue 22 Oct 2019, 3:00pm
Harmonic Analysis Seminar
MATH 126
TBA
MATH 126
Tue 22 Oct 2019, 3:00pm-4:00pm
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UBC
Tue 22 Oct 2019, 4:00pm
Discrete Math Seminar
ESB 4127
Graph information ratio
ESB 4127
Tue 22 Oct 2019, 4:00pm-5:00pm

Abstract

Inspired by a problem in joint source-channel coding, we introduce a new notion of similarity between graphs, termed graph information ratio. We discuss various properties of this measure, including in particular metric structure and partial ordering of graphs, an information ratio power inequality, relations to graph homomorphism, algebraic identities and inequalities, and more.
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UBC Math
Fri 25 Oct 2019, 3:00pm
Department Colloquium
ESB 1012
TBA
ESB 1012
Fri 25 Oct 2019, 3:00pm-4:00pm

Abstract


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UBC
Mon 28 Oct 2019, 3:00pm
Algebraic Geometry Seminar
MATH 225
TBA
MATH 225
Mon 28 Oct 2019, 3:00pm-5:00pm

Abstract

 TBA
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Brian Chan
UBC
Tue 29 Oct 2019, 4:00pm
Discrete Math Seminar
ESB 4127
TBA
ESB 4127
Tue 29 Oct 2019, 4:00pm-5:00pm

Abstract

 
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Alex Hening
Tufts University
Wed 30 Oct 2019, 3:00pm
Mathematical Biology Seminar / Probability Seminar
ESB 1012
Stochastic persistence and extinction
ESB 1012
Wed 30 Oct 2019, 3:00pm-4:00pm

Abstract

A key question in population biology is understanding the conditions under which the species of an ecosystem persist or go extinct. Theoretical and empirical studies have shown that persistence can be facilitated or negated by both biotic interactions and environmental fluctuations. We study the dynamics of n interacting species that live in a stochastic environment. Our models are described by n dimensional piecewise deterministic Markov processes. These are processes (X(t), r(t)) where the vector X denotes the density of the n species and r(t) is a finite state space process which keeps track of the environment. In any fixed environment the process follows the flow given by a system of ordinary differential equations. The randomness comes from the changes or switches in the environment, which happen at random times. We give sharp conditions under which the populations persist as well as conditions under which some populations go extinct exponentially fast. As an example we look at the competitive exclusion principle from ecology and show how the random switching can `rescue' species from extinction.
 
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University of Victoria
Mon 4 Nov 2019, 3:00pm
Algebraic Geometry Seminar
MATH 225
TBA
MATH 225
Mon 4 Nov 2019, 3:00pm-4:00pm

Abstract

 TBA
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University of Calgary
Mon 4 Nov 2019, 4:10pm
Algebraic Geometry Seminar
MATH 225
MATH 225
Mon 4 Nov 2019, 4:10pm-5:10pm

Abstract

 TBA
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Professor Melanie Matchett Wood
UC Berkeley
Fri 8 Nov 2019, 3:00pm SPECIAL
Department Colloquium
ESB2012
PIMS-UBC Distinguished Colloquium
ESB2012
Fri 8 Nov 2019, 3:00pm-4:00pm

Abstract

 
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Fri 15 Nov 2019, 3:00pm
Department Colloquium
ESB 1012
(reserved for PIMS UBC Mathematical Sciences Young Faculty Award)
ESB 1012
Fri 15 Nov 2019, 3:00pm-4:00pm

Abstract

A link to be provided later.
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UBC
Mon 18 Nov 2019, 3:00pm
Algebraic Geometry Seminar
MATH 225
TBA
MATH 225
Mon 18 Nov 2019, 3:00pm-5:00pm

Abstract

 TBA
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Thomas Hockenhull
University of Glasgow
Wed 20 Nov 2019, 2:45pm
Topology and related seminars
PIMS
TBA
PIMS
Wed 20 Nov 2019, 2:45pm-3:45pm

Abstract

 
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University of Michigan
Thu 21 Nov 2019, 3:00pm
Algebraic Geometry Seminar
MATH 225
MATH 225
Thu 21 Nov 2019, 3:00pm-5:00pm

Abstract

 TBA
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Dept of Mathematics, University of Cincinnati
Fri 22 Nov 2019, 3:00pm
Department Colloquium
ESB 1012
Microswimmers propelled by helical flagella: Modeling, Simulations & Analysis
ESB 1012
Fri 22 Nov 2019, 3:00pm-4:00pm

Abstract

 Swimming bacteria with helical flagella are self-propelled micro-swimmers in nature, and the swimming strategies of such bacteria vary depending on the number and the position of flagella on the cell body. In this talk, I will introduce two microorganisms, multi-flagellated E. coli and single-flagellated Vibrio A. The Kirchhoff rod theory is used to model the elastic helical flagella and the rod-shaped cell body is represented by a hollow ellipsoid that can translate and rotate as a neutrally buoyant rigid body interacting with a surrounding fluid. The hydrodynamic interaction between the fluid and the bacteria is described by the regularized version of Stokes flow. I will focus on how bacteria can swim and reorient swimming course for survival and how Mathematics can help to understand the swimming mechanism of such bacteria.

 

 

Keywords: Fluid-structure interaction, Bacterial flagellar propulsion, Polymorphic transformation, Buckling instability


Note for Attendees

 Refreshments are served at PIMS before the Colloquium
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UBC
Mon 25 Nov 2019, 3:00pm
Algebraic Geometry Seminar
MATH 225
TBA
MATH 225
Mon 25 Nov 2019, 3:00pm-5:00pm

Abstract

 TBA
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Yu-Hsiang Liu
UBC
Mon 2 Dec 2019, 3:00pm
Algebraic Geometry Seminar
MATH 225
TBA
MATH 225
Mon 2 Dec 2019, 3:00pm-5:00pm

Abstract

 TBA
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Charles Collot
Courant Institute
Tue 3 Dec 2019, 3:30pm
Diff. Geom, Math. Phys., PDE Seminar
TBA
TBA
TBA
Tue 3 Dec 2019, 3:30pm-4:30pm

Abstract

 
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University of Queensland
Tue 14 Jan 2020, 4:00pm
Discrete Math Seminar
ESB 4127
ESB 4127
Tue 14 Jan 2020, 4:00pm-5:00pm

Abstract


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