Scientific

Gaps of saddle connection directions for some branched covers of tori

Speaker: 
Anthony Sanchez
Date: 
Thu, May 14, 2020
Location: 
Zoom
Conference: 
Pacific Dynamics Seminar
Abstract: 

TBA

Class: 

Real-time modelling of the COVID-19 epidemic: perspectives from British Columbia

Speaker: 
Caroline Colijn
Daniel Coombs
Date: 
Thu, May 14, 2020
Location: 
Zoom
Conference: 
bcCOVID-19group public seminar
Abstract: 

The COVID-19 global pandemic has led to unprecedented public interest in mathematical modelling as a tool to understand the dynamics of disease spread and predict the impact of public health interventions. In this pair of talks, we will describe how mathematical models are being used, with particular reference to the British Columbia epidemic.

In the first talk, Prof. Caroline Colijn (Dept. of Mathematics, Simon Fraser University) will outline the key features of the British Columbia data and focus on how modelling has allowed us to estimate the effectiveness of the provincial response. In the second talk, Prof. Daniel Coombs (Dept. of Mathematics and Inst. of Applied Mathematics, University of British Columbia) will describe forward-looking modelling approaches that can provide some guidance as the province moves towards partial de-escalation of measures. Each talk will be 30 mins in length and followed by a question and discussion period.

For more details on the group's work and to contact the team, please visit https://bccovid-19group.ca/

Class: 

Factors of Gibbs measures on subshifts (2 of 2)

Speaker: 
Sophie MacDonald
Date: 
Thu, May 7, 2020
Location: 
Zoom
Conference: 
Pacific Dynamics Seminar
Abstract: 

Classical results of Dobrushin and Lanford-Ruelle establish, in rough terms, that for a local energy function on a subshift without too much long-range order, the translation-invariant Gibbs measures are precisely the equilibrium measures. There are multiple definitions of a Gibbs measure in the literature, which do not always coincide. We will discuss two of these definitions, one introduced by Capocaccia and the other used by Dobrushin-Lanford-Ruelle, and outline a proof (available at arxiv.org/abs/2003.05532) that they are equivalent.

We will also discuss forthcoming work, in which we show that Gibbsianness is preserved by pushforward through a certain kind of almost invertible factor map. As an application in one dimension, we show that for a sufficiently regular potential, any equilibrium measure on an irreducible sofic shift is Gibbs. As far as we know, this is the first reasonably general result of the Lanford-Ruelle type for a class of subshifts without the topological Markov property.

Joint work with Luísa Borsato, with extensive advice from Brian Marcus and Tom Meyerovitch.

This lecture was given in two parts. The video on this page was given as a follow up to a pre-recorded video.

Class: 
Subject: 

What is epithelial-mesenchymal plasticity and why is it important for metastasis?

Speaker: 
Herbert Levine
Date: 
Wed, May 6, 2020
Location: 
Zoom
University of British Columbia, Vancouver, Canada
Conference: 
Mathematical Biology Seminar
Abstract: 

Until very recently most cancer biologists operated with the assumption that the most common route to metastasis involved cells of the primary tumor transforming to a motile single-cell phenotype via complete EMT (the epithelial-mesenchymal transition). This change allowed them to migrate individually to distant organs, eventually leading to clonal growths in other locations. But, a new more nuanced picture has been emerging, based on advanced measurements and on computational systems biology approaches. It has now been realized that cells can readily adopt states with hybrid properties, use these properties to move collectively and cooperatively, and reach distant niches as highly metastatic clusters. This talk will focus on the accumulating evidence for this revised perspective, the role of biological physics theory in instigating this whole line of investigation, and on open questions currently under investigation.

Class: 

Rigidity of Geodesic Planes in Hyberbolic Manifolds

Speaker: 
Osama Khalil
Date: 
Tue, May 5, 2020
Location: 
Zoom
Conference: 
Online working seminar in Ergodic Theory
University of Utah Seminar in Ergodic Theory
Abstract: 

TBA

Class: 
Subject: 

Factors of Gibbs measures on subshifts (1 of 2)

Speaker: 
Sophie MacDonald
Date: 
Thu, May 7, 2020
Location: 
Zoom
Conference: 
Pacific Dynamics Seminar
Abstract: 

Classical results of Dobrushin and Lanford-Ruelle establish, in rough terms, that for a local energy function on a subshift without too much long-range order, the translation-invariant Gibbs measures are precisely the equilibrium measures. There are multiple definitions of a Gibbs measure in the literature, which do not always coincide. We will discuss two of these definitions, one introduced by Capocaccia and the other used by Dobrushin-Lanford-Ruelle, and outline a proof (available at [arxiv.org/abs/2003.05532]) that they are equivalent.

We will also discuss forthcoming work, in which we show that Gibbsianness is preserved by pushforward through a certain kind of almost invertible factor map. As an application in one dimension, we show that for a sufficiently regular potential, any equilibrium measure on an irreducible sofic shift is Gibbs. As far as we know, this is the first reasonably general result of the Lanford-Ruelle type for a class of subshifts without the topological Markov property.

Joint work with Luísa Borsato, with extensive advice from Brian Marcus and Tom Meyerovitch.

This lecture was given in two parts. The video on this page was distributed as a pre-recorded session ahead of a second live lecture.

Class: 
Subject: 

Quantum Unique Ergodicity

Speaker: 
Lior Silberman
Date: 
Thu, Apr 30, 2020
Location: 
Zoom
Conference: 
Pacific Dynamics Seminar
Abstract: 

TBA

Class: 
Subject: 

Caroline Series' The modular surface and continued fractions

Speaker: 
Claire Merriman
Date: 
Tue, Apr 21, 2020
Location: 
Zoom
Conference: 
Online working seminar in Ergodic Theory
University of Utah Seminar in Ergodic Theory
Abstract: 

Caroline Series' The modular surface and continued fractions

Class: 
Subject: 

Effective Equidistribution of Horospherical Flows in Infinite Volume

Speaker: 
Nattalie Tamam
Date: 
Thu, Apr 23, 2020
Location: 
Zoom
Conference: 
Pacific Dynamics Seminar
Abstract: 

The horospherical flow on finite-volume hyperbolic surfaces is well-understood. In particular, effective equidistribution of non-closed horospherical orbits is known. New difficulties arise when studying the infinite-volume setting. We will discuss the setting in finite- and infinite-volume manifolds, and the measures that play a crucial role in the latter. Joint work with Jacqueline Warren.

Class: 
Subject: 

Modeling strict age-targeted mitigation strategies for COVID-19

Speaker: 
Wesley Pegden
Date: 
Wed, Apr 22, 2020
Location: 
PIMS, University of British Columbia
Zoom
Conference: 
Mathematical Biology Seminar
Abstract: 

In this talk, we will use compartmental models to examine the power of age-targeted mitigation strategies for COVID-19. We will present evidence that, in the context of strategies which end with herd immunity, age-heterogeneous strategies are better for reducing direct mortalities across a wide parameter regime. And using a model which integrates empirical data on age-contact patterns in the United States and recent estimates of COVID-19 mortality and hospitalization rates, we will present evidence that age-targeted approaches have the potential to greatly reduce mortalities and ICU utilization for COVID-19, among strategies which ultimately end the epidemic by reaching herd immunity. This is joint work with Maria Chikina.

Class: 

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