Mathematics

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
CRG: 
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: 
University of Utah Seminar in Ergodic Theory
CRG: 
Abstract: 

TBA

Subject: 
Class: 

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: 
University of Utah Seminar in Ergodic Theory
CRG: 
Abstract: 

Caroline Series' The modular surface and continued fractions

Subject: 
Class: 

Effective Equidistribution of Horospherical Flows in Infinite Volume

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

Subject: 
Class: 

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
CRG: 
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: 

Boshernitzan's criterion for unique ergodicity

Speaker: 
Jon Chiaka
Date: 
Tue, Apr 14, 2020
Location: 
University of Utah
Zoom
Conference: 
University of Utah Seminar in Ergodic Theory
CRG: 
Abstract: 

TBA

Subject: 
Class: 

Multiple fission cycles in Chlamydomonas

Speaker: 
John Tyson
Date: 
Wed, Apr 8, 2020
Location: 
PIMS, University of British Columbia
Zoom
Conference: 
Mathematical Biology Seminar
CRG: 
Abstract: 

In this talk I will present a "dynamical paradigm" for modeling networks of interacting genes and proteins that regulate every aspect of cell physiology. The paradigm is based on dynamical systems theory of nonlinear ODEs, especially one- and two-parameter bifurcation diagrams. I will show how we have used this paradigm to unravel the mechanisms controlling "multiple fission" cycles in the photosynthetic green alga Chlamydomonas. While most eukaryotic cells maintain a characteristic size by executing binary division after each mass doubling, Chlamydomonas cells can grow more than eight-fold during daytime before undergoing rapid cycles of DNA replication, mitosis and cell division at night, which produce up to 16 daughter cells. We propose that this unusual strategy of growth and division (which is clearly advantageous for a photosynthetic organism) can be governed by a size-dependent bistable switch that turns on and off a limit cycle oscillator that drives cells through rapid cycles of DNA synthesis and mitosis. We show that this simple ‘sizer-oscillator’ arrangement reproduces the experimentally observed features of multiple-fission cycles and the response of Chlamydomonas cells to different light-dark regimes. Our model makes unexpected predictions about the size-dependence of the time of onset of cell-cycle oscillations after cells are transferred from light to dark conditions, and these predictions are confirmed by single-cell experiments.

 

Collaborators: Stefan Heldt and Bela Novak (Oxford Univ) on the modeling; Fred Cross (Rockefeller Univ) on the experiments.

Class: 

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