Monday, December 7th, 2020

Time: 3:00-4:00p.m.  Place: Online (register)

Speaker: Dr. Margaret E. Roberts
Associate Professor
Department of Political Science and the Halıcıoğlu Data Science Institute
University of California, San Diego

Title: Resilience to Online Censorship

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Abstract: 
To what extent are Internet users resilient to online censorship? When does censorship influence consumption of information and when does it create backlash? Drawing on data reflecting censorship evasion of the Great Firewall of China, I examine the extent to which individuals affected by censorship seek out ways to route around it. Using censorship events of Wikipedia and Instagram and crisis events like the outbreak of COVID, I examine how changes in the censorship and political environment influence censorship evasion. I find that crisis, as well as censorship of very popular and addictive websites, can create incentives for censorship evasion that in turn provides a gateway to long censored and sensitive political information. But, in the absence of a strong incentive to jump the wall, censorship events cut off access not only to political information, but also to opportunities for exploration and learning. Based on joint work with Jennifer Pan, Will Hobbs, Keng-Chi Chang, and Zachary Steinert-Threlkeld.

Profile: 
Dr. Roberts is Associate Professor in the Department of Political Science and the Halıcıoğlu Data Science Institute at the University of California, San Diego. She is also part of the Omni-Methods Group. Her research interests lie in the intersection of political methodology and the politics of information, with a specific focus on methods of automated content analysis and the politics of censorship and propaganda in China. Roberts received a PhD from Harvard in Government (2014), a MS from Stanford in Statistics (2009), and BA from Stanford in International Relations and Economics (2009). Much of her research uses social media, online experiments, and large collections of texts to understand the influence of censorship and propaganda on access to information and beliefs about politics. Her book, Censored: Distraction and Diversion Inside China’s Great Firewall, published by Princeton University Press in 2018, was listed as one of the Foreign Affairs Best Books of 2018, was honoured with the Goldsmith Book Award, and has been awarded the Best Book Award in the Human Rights Section and Information Technology and Politics Section of the American Political Science Association. She also holds a Chancellor’s Associates Endowed Chair at UCSD.

ARES is a collaboration between CANSSI Ontario and its partner universities.

Friday, November 20th, 2020

Time: 2:30 p.m.  Place: Online (via Zoom)

Speaker: Nicolas Fraiman (University of North Carolina)

Title: Stochastic Recursions on Random Graphs.

Abstract: We study a family of Markov processes on directed graphs where the values at each vertex are influenced by the values of its inbound neighbors and by independent fluctuations either on the vertices themselves or on the edges connecting them to their inbound neighbors. Typical examples include PageRank and other information propagation processes. Assuming a stationary distribution exists for this Markov chain, our goal is to characterize the marginal distribution of a uniformly chosen vertex in the graph. In order to obtain a meaningful characterization, we assume that the underlying graph is either a directed configuration graph or an inhomogeneous random digraph, both of which are known to converge, in the local weak sense, to a marked Galton-Watson process. We prove that the stationary distribution on the graph converges in a Wasserstein metric to a function of i.i.d. copies of the special endogenous solution to a branching distributional fixed-point equation. This is joint work with Mariana Olvera-Cravioto and Tzu-Chi Lin.

Nicolas Fraiman is an Assistant Professor in the Department of Statistics and Operations Research at the University of North Carolina at Chapel Hill. He obtained his Ph.D. from McGill University in 2013. He was a Postdoctoral Fellow at the University of Pennsylvania and Harvard University. He works on the probabilistic analysis of random structures, stochastic dynamics, randomized algorithms and combinatorial statistics.

Friday, November 6th, 2020

Time: 2:30 p.m.  Place: Online (via Zoom)

Speaker: Florian Richter (Northwestern University)

Title: Dynamical generalizations of the Prime Number Theorem and disjointness of additive and multiplicative actions.

Abstract: One of the fundamental challenges in number theory is to understand the intricate way in which the additive and multiplicative structures in the integers intertwine. We will explore a dynamical approach to this topic. After introducing a new dynamical framework for treating questions in multiplicative number theory, we will present an ergodic theorem which contains various classical number-theoretic results, such as the Prime Number Theorem, as special cases. This naturally leads to a formulation of an extended form of Sarnak's Mobius randomness conjecture, which deals with the disjointness of actions of (N,+) and (N,*). This talk is based on joint work with Vitaly Bergelson.

Florian Richter is a Boas Assistant Professor in the Department of Mathematics at Northwestern University. He received his Ph.D. from The Ohio State University in 2018 under the supervision of Vitaly Bergelson. He received The Elizabeth Clay Howald Presidential Fellowship and Louise B.C. Vetter award for excellence in research from Ohio State. He works on dynamical systems, combniatorics and number theory.

Friday, October 16th, 2020

Time: 2:30 p.m.  Place: Online (via Zoom)

Speaker: Rafael Potrie (Universidad de la Republica-Uruguay)

Title: Anosov flows and the fundamental group.

Abstract: The hairy ball theorem says that a vector field in the sphere must have some singularity. How does the dynamics interact with the topology of the underlying manifold in higher dimensions? We will discuss some instances of this question for dynamics in 3-manifolds, featuring a beautiful result due to Margulis and Plante-Thurston. Time permitting, we will touch upon more recent developments on the interactions between the topology and dynamics in 3 dimensions.

Rafael Potrie is an Associate Professor at the Universidad de la Republica-Uruguay. He obtained his Ph.D. in Mathematics from Universite Paris 13/Universidad de la Republica-Uruguay in 2012. He was an invited speaker of the Dynamical Systems session at the International Congress of Mathematicians (ICM) in 2018. His research mainly concerns the topological classification of partially hyperbolic systems in three-dimensional manifolds and its dynamical consequences. Other interests include smooth dynamics, ergodic theory, discrete subgroups of Lie groups, and the geometry of foliations and laminations.

Friday, October 2nd, 2020

Time: 2:30 p.m.  Place: Online (via Zoom)

Speaker: Elliot Paquette (McGill University)

Title: Random perturbations of non-normal matrices.

Abstract: Suppose one wants to calculate the eigenvalues of a large, non-normal matrix. For example, consider the matrix which is 0 in most places except above the diagonal, where it is 1. The eigenvalues of this matrix are all 0. Similarly, if one conjugates this matrix, in exact arithmetic one would get all eigenvalues equal to 0. However, when one makes floating point errors, the eigenvalues of this matrix are dramatically different. One can model these errors as performing a small, random perturbation to the matrix. And, far from being random, the eigenvalues of this perturbed matrix nearly exactly equidistribute on the unit circle of the complex plane. This talk will give a probabilistic explanation of why this happens and discuss the general question: how does one predict the eigenvalues of a large, non-normal, randomly perturbed matrix?

Elliot Paquette is an Assistant Professor within the Department of Mathematics and Statistics at McGill University. He obtained his Ph.D.~in Mathematics from the University of Washington in 2013. He was an NSF Postdoctoral Fellow at the Weizmann Institute of Science from 2013-2016, and an Assistant Professor at the Ohio State University from 2016-2020. His research is in probability theory, with a focus on random matrix theory and on problems with geometric and topological inspirations.