Department of Mathematics and Statistics - Department Colloquium
https://www.queensu.ca/mathstat/seminars/colloquium
Department Colloquium
enDepartment Colloquium - Ian Frankel (Queen's University)
https://www.queensu.ca/mathstat/department-colloquium-ian-frankel-queens-university
<div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even" property="content:encoded"><div class="tex2jax"><h2>Department Colloquium</h2>
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<p><a href="/mathstat/sites/webpublish.queensu.ca.mastwww/files/images/news_and_seminars/colloquium/nov_27_2020.jpg"><img alt="Ian Frankel (Queen's University)" src="/mastwww/sites/webpublish.queensu.ca.mastwww/files/images/news_and_seminars/colloquium/nov_27_2020.jpg" style="width: 245px; height: 343px;" /></a></p>
</div>
<h3>Friday, November 27th, 2020</h3>
<p><strong>Time:</strong> 2:30 p.m. <strong>Place:</strong> Online (via Zoom)</p>
<p><strong>Speaker:</strong> Ian Frankel (Queen's University)</p>
<p><strong>Title:</strong> Invariant measures for straight line flows.</p>
<p><strong>Abstract: </strong> We discuss the question of equidistribution of billiard trajectories in polygons. As it turns out, for polygons whose angles are rational, this is related to the geometry of a 1-parameter family of surfaces in a moduli space. We will describe how the possible measures with respect to which a billiard trajectory may equidistribute are constrained by this 1-parameter family of surfaces.</p>
<p><strong>Ian Frankel</strong> is a Coleman Research Fellow within the Department of Mathematics and Statistics at Queen’s University. He obtained his Ph.D. in Mathematics from the University of Chicago in 2018. He was a Research Fellow at the Higher School of Economics and a Fields Postdoctoral Fellow at The Fields Institute for Research in Mathematical Sciences. He is mainly interested in geometry and topology and dynamical systems.</p>
</div></div></div></div><div class="field field-name-field-tag field-type-taxonomy-term-reference field-label-above"><div class="field-label">Tags: </div><div class="field-items"><div class="field-item even"><a href="/mathstat/news" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">News</a></div><div class="field-item odd"><a href="/mathstat/seminars-announce" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">Seminars</a></div><div class="field-item even"><a href="/mathstat/seminars/colloquium" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">Department Colloquium</a></div></div></div>Fri, 27 Nov 2020 20:56:46 +0000cowellj651 at https://www.queensu.ca/mathstatDepartment Colloquium - Nicolas Fraiman (U of North Carolina)
https://www.queensu.ca/mathstat/department-colloquium-nicolas-fraiman-u-north-carolina
<div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even" property="content:encoded"><div class="tex2jax"><h2>Department Colloquium</h2>
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<p><a href="/mathstat/sites/webpublish.queensu.ca.mastwww/files/images/news_and_seminars/colloquium/nov_20_2020.png"><img alt="Nicolas Fraiman (University of North Carolina)" src="/mastwww/sites/webpublish.queensu.ca.mastwww/files/images/news_and_seminars/colloquium/nov_20_2020.png" style="width: 450px; height: 236px;" /></a></p>
</div>
<h3>Friday, November 20th, 2020</h3>
<p><strong>Time:</strong> 2:30 p.m. <strong>Place:</strong> Online (via Zoom)</p>
<p><strong>Speaker:</strong> Nicolas Fraiman (University of North Carolina)</p>
<p><strong>Title:</strong> Stochastic Recursions on Random Graphs.</p>
<p><strong>Abstract: </strong> 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.</p>
<p><strong>Nicolas Fraiman</strong> 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.</p>
</div></div></div></div><div class="field field-name-field-tag field-type-taxonomy-term-reference field-label-above"><div class="field-label">Tags: </div><div class="field-items"><div class="field-item even"><a href="/mathstat/news" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">News</a></div><div class="field-item odd"><a href="/mathstat/seminars-announce" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">Seminars</a></div><div class="field-item even"><a href="/mathstat/seminars/colloquium" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">Department Colloquium</a></div></div></div>Fri, 20 Nov 2020 20:56:46 +0000cowellj644 at https://www.queensu.ca/mathstatDepartment Colloquium - Yaiza Canzani (U of North Carolina)
https://www.queensu.ca/mathstat/department-colloquium-yaiza-canzani-u-north-carolina
<div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even" property="content:encoded"><div class="tex2jax"><h2>Department Colloquium</h2>
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<p><a href="/mathstat/sites/webpublish.queensu.ca.mastwww/files/images/news_and_seminars/colloquium/nov_13_2020.png"><img alt="Yaiza Canzani (University of North Carolina)" src="/mastwww/sites/webpublish.queensu.ca.mastwww/files/images/news_and_seminars/colloquium/nov_13_2020.png" style="width: 450px; height: 246px;" /></a></p>
</div>
<h3>Friday, November 13th, 2020</h3>
<p><strong>Time:</strong> 2:30 p.m. <strong>Place:</strong> Online (via Zoom)</p>
<p><strong>Speaker:</strong> Yaiza Canzani (University of North Carolina)</p>
<p><strong>Title:</strong> Eigenfunction concentration via geodesic beams.</p>
<p><strong>Abstract: </strong> A vast array of physical phenomena, ranging from the propagation of waves to the location of quantum particles, is dictated by the behavior of Laplace eigenfunctions. Because of this, it is crucial to understand how various measures of eigenfunction concentration respond to the background dynamics of the geodesic flow. In collaboration with J. Galkowski, we developed a framework to approach this problem that hinges on decomposing eigenfunctions into geodesic beams. In this talk, I will present these techniques and explain how to use them to obtain quantitative improvements on the standard estimates for the eigenfunction's pointwise behavior, Lp norms, and for both pointwise and integrated Weyl Laws. One consequence of this method is a quantitatively improved Weyl Law for the eigenvalue counting function on all product manifolds.</p>
<p><strong>Yaiza Canzani</strong> is an Assistant Professor in the Department of Mathematics at the University of North Carolina at Chapel Hill. She was awarded a Sloan Research Fellowship in 2018. Before joining UNC, Prof. Canzani was a Benjamin Peirce Fellow at Harvard University and a member of the Institute for Advanced Study. She obtained her Ph.D. from McGill University in 2013 under the supervision of Dmitry Jakobson and John Toth. She works on geometric analysis and spectral theory.</p>
</div></div></div></div><div class="field field-name-field-tag field-type-taxonomy-term-reference field-label-above"><div class="field-label">Tags: </div><div class="field-items"><div class="field-item even"><a href="/mathstat/news" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">News</a></div><div class="field-item odd"><a href="/mathstat/seminars-announce" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">Seminars</a></div><div class="field-item even"><a href="/mathstat/seminars/colloquium" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">Department Colloquium</a></div></div></div>Fri, 13 Nov 2020 20:56:46 +0000cowellj639 at https://www.queensu.ca/mathstatDepartment Colloquium - Florian Richter (Northwestern University)
https://www.queensu.ca/mathstat/department-colloquium-florian-richter-northwestern-university
<div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even" property="content:encoded"><div class="tex2jax"><h2>Department Colloquium</h2>
<hr style="height:1px;border:none;color:lightgrey;background-color:lightgrey;" /><div class="image-right">
<p><a href="/mathstat/sites/webpublish.queensu.ca.mastwww/files/images/news_and_seminars/colloquium/nov_6_2020.jpg"><img alt="Florian Richter (Northwestern University)" src="/mastwww/sites/webpublish.queensu.ca.mastwww/files/images/news_and_seminars/colloquium/nov_6_2020.jpg" style="width: 450px; height: 338px;" /></a></p>
</div>
<h3>Friday, November 6th, 2020</h3>
<p><strong>Time:</strong> 2:30 p.m. <strong>Place:</strong> Online (via Zoom)</p>
<p><strong>Speaker:</strong> Florian Richter (Northwestern University)</p>
<p><strong>Title:</strong> Dynamical generalizations of the Prime Number Theorem and disjointness of additive and multiplicative actions.</p>
<p><strong>Abstract: </strong> 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.</p>
<p><strong>Florian Richter</strong> 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.</p>
</div></div></div></div><div class="field field-name-field-tag field-type-taxonomy-term-reference field-label-above"><div class="field-label">Tags: </div><div class="field-items"><div class="field-item even"><a href="/mathstat/news" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">News</a></div><div class="field-item odd"><a href="/mathstat/seminars-announce" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">Seminars</a></div><div class="field-item even"><a href="/mathstat/seminars/colloquium" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">Department Colloquium</a></div></div></div>Fri, 06 Nov 2020 20:56:46 +0000cowellj638 at https://www.queensu.ca/mathstatDepartment Colloquium - Emine Yildirim (Queen’s University)
https://www.queensu.ca/mathstat/department-colloquium-emine-yildirim-queen%E2%80%99s-university
<div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even" property="content:encoded"><div class="tex2jax"><h2>Department Colloquium</h2>
<hr style="height:1px;border:none;color:lightgrey;background-color:lightgrey;" /><div class="image-right">
<p><a href="/mathstat/sites/webpublish.queensu.ca.mastwww/files/images/news_and_seminars/colloquium/oct_23_2020.png"><img alt="Emine Yildirim (Queen’s University)" src="/mastwww/sites/webpublish.queensu.ca.mastwww/files/images/news_and_seminars/colloquium/oct_23_2020.png" style="width: 450px; height: 342px;" /></a></p>
</div>
<h3>Friday, October 23rd, 2020</h3>
<p><strong>Time:</strong> 2:30 p.m. <strong>Place:</strong> Online (via Zoom)</p>
<p><strong>Speaker:</strong> Emine Yildirim (Queen’s University)</p>
<p><strong>Title:</strong> Graphs and Combinatorics in Representation Theory of Algebras.</p>
<p><strong>Abstract: </strong> Representation theorists of ﬁnite dimensional algebras often use quivers, also known as directed graphs, and many other combinatorial tools associated with these quivers. This is because we understand the module category of algebras via representation of quivers. On the other hand, we also capture the beautiful combinatorics of cluster algebras via the same representation theory. In this talk, I will outline how this machinery works along with some recent results on Cluster Categories we obtained joint with Charles Paquette using the combinatorics and representations theory of quivers.</p>
<p><strong>Emine Yildirim</strong> is a Coleman Research Fellow within the Department of Mathematics and Statistics at Queen’s University. She obtained her Ph.D. in Mathematics from the Universite du Quebec a Montreal in 2018. She is mainly interested in representation theory of algebras, speciﬁcally path algebras, incidence algebras, and their representations. She also works on cluster algebras, their categoriﬁcation and related combinatorics.</p>
</div></div></div></div><div class="field field-name-field-tag field-type-taxonomy-term-reference field-label-above"><div class="field-label">Tags: </div><div class="field-items"><div class="field-item even"><a href="/mathstat/news" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">News</a></div><div class="field-item odd"><a href="/mathstat/seminars-announce" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">Seminars</a></div><div class="field-item even"><a href="/mathstat/seminars/colloquium" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">Department Colloquium</a></div></div></div>Fri, 23 Oct 2020 13:43:50 +0000cowellj635 at https://www.queensu.ca/mathstatDepartment Colloquium - Rafael Potrie (U de la Republica-Uruguay)
https://www.queensu.ca/mathstat/department-colloquium-rafael-potrie-u-de-la-republica-uruguay
<div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even" property="content:encoded"><div class="tex2jax"><h2>Department Colloquium</h2>
<hr style="height:1px;border:none;color:lightgrey;background-color:lightgrey;" /><div class="image-right">
<p><a href="/mathstat/sites/webpublish.queensu.ca.mastwww/files/images/news_and_seminars/colloquium/oct_16_2020.jpg"><img alt="Rafael Potrie (Universidad de la Republica-Uruguay)" src="/mastwww/sites/webpublish.queensu.ca.mastwww/files/images/news_and_seminars/colloquium/oct_16_2020.jpg" style="width: 450px; height: 338px;" /></a></p>
</div>
<h3>Friday, October 16th, 2020</h3>
<p><strong>Time:</strong> 2:30 p.m. <strong>Place:</strong> Online (via Zoom)</p>
<p><strong>Speaker:</strong> Rafael Potrie (Universidad de la Republica-Uruguay)</p>
<p><strong>Title:</strong> Anosov flows and the fundamental group.</p>
<p><strong>Abstract: </strong> 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.</p>
<p><strong>Rafael Potrie</strong> 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.</p>
</div></div></div></div><div class="field field-name-field-tag field-type-taxonomy-term-reference field-label-above"><div class="field-label">Tags: </div><div class="field-items"><div class="field-item even"><a href="/mathstat/news" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">News</a></div><div class="field-item odd"><a href="/mathstat/seminars-announce" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">Seminars</a></div><div class="field-item even"><a href="/mathstat/seminars/colloquium" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">Department Colloquium</a></div></div></div>Fri, 16 Oct 2020 20:56:46 +0000cowellj633 at https://www.queensu.ca/mathstatDepartment Colloquium - Farouk Nathoo (University of Victoria)
https://www.queensu.ca/mathstat/department-colloquium-farouk-nathoo-university-victoria
<div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even" property="content:encoded"><div class="tex2jax"><h2>Department Colloquium</h2>
<hr style="height:1px;border:none;color:lightgrey;background-color:lightgrey;" /><div class="image-right">
<p><a href="/mathstat/sites/webpublish.queensu.ca.mastwww/files/images/news_and_seminars/colloquium/oct_9_2020.png"><img alt="Farouk Nathoo (University of Victoria)" src="/mastwww/sites/webpublish.queensu.ca.mastwww/files/images/news_and_seminars/colloquium/oct_9_2020.png" style="width: 450px; height: 219px;" /></a></p>
</div>
<h3>Friday, October 9th, 2020</h3>
<p><strong>Time:</strong> 2:30 p.m. <strong>Place:</strong> Online (via Zoom)</p>
<p><strong>Speaker:</strong> Farouk Nathoo (University of Victoria)</p>
<p><strong>Title:</strong> Spatial Statistical Modeling for Neuroimaging Data.</p>
<p><strong>Abstract: </strong> I will describe three projects involving the analysis of neuroimaging data and the development of hierarchical spatial Bayesian models for each. In the first, we develop an approach for determining the location and dynamics of brain activity from combined magnetoencephalography and electroencephalography data. The resulting inverse problem is ill-posed and we propose a distributed solution based on a Bayesian spatial finite mixture model that incorporates the Potts model to represent the spatial dependence in an allocation process that partitions the cortical surface into a small number of latent states. In the second project, we consider statistical modelling of functional magnetic resonance imaging (fMRI) data which is challenging in part as the data are both spatially and temporally correlated. Motivated by an event‐related fMRI experiment, we propose a novel hierarchical Bayesian model with automatic selection of the auto‐regressive orders of the noise process that vary spatially over the brain. In the third project, we develop a Bayesian bivariate spatial model for multivariate regression analysis applicable to studies examining the influence of genetic variation on brain structure. Our model is motivated by an imaging genetics study of the Alzheimer's Disease Neuroimaging Initiative, where the objective is to examine the association between images of volumetric and cortical thickness values summarizing the structure of the brain as measured by magnetic resonance imaging (MRI) and a set of 486 SNPs from 33 Alzheimer's Disease (AD) candidate genes obtained from 632 subjects. A bivariate spatial process model is developed to accommodate the correlation structures typically seen in structural brain imaging data and we develop a mean-field variational Bayes algorithm and a Gibbs sampling algorithm to fit the model. We compare the new spatial model to an existing non-spatial model in our motivating application.</p>
</div></div></div></div><div class="field field-name-field-tag field-type-taxonomy-term-reference field-label-above"><div class="field-label">Tags: </div><div class="field-items"><div class="field-item even"><a href="/mathstat/news" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">News</a></div><div class="field-item odd"><a href="/mathstat/seminars-announce" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">Seminars</a></div><div class="field-item even"><a href="/mathstat/seminars/colloquium" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">Department Colloquium</a></div></div></div>Fri, 09 Oct 2020 20:56:46 +0000cowellj630 at https://www.queensu.ca/mathstatDepartment Colloquium - Elliot Paquette (McGill University)
https://www.queensu.ca/mathstat/department-colloquium-elliot-paquette-mcgill-university
<div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even" property="content:encoded"><div class="tex2jax"><h2>Department Colloquium</h2>
<hr style="height:1px;border:none;color:lightgrey;background-color:lightgrey;" /><div class="image-right">
<p><a href="/mathstat/sites/webpublish.queensu.ca.mastwww/files/images/news_and_seminars/colloquium/oct_2_2020.png"><img alt="Elliot Paquette (McGill University)" src="/mastwww/sites/webpublish.queensu.ca.mastwww/files/images/news_and_seminars/colloquium/oct_2_2020.png" style="width: 450px; height: 208px;" /></a></p>
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<h3>Friday, October 2nd, 2020</h3>
<p><strong>Time:</strong> 2:30 p.m. <strong>Place:</strong> Online (via Zoom)</p>
<p><strong>Speaker:</strong> Elliot Paquette (McGill University)</p>
<p><strong>Title:</strong> Random perturbations of non-normal matrices.</p>
<p><strong>Abstract: </strong> 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?</p>
<p><strong>Elliot Paquette</strong> 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.</p>
</div></div></div></div><div class="field field-name-field-tag field-type-taxonomy-term-reference field-label-above"><div class="field-label">Tags: </div><div class="field-items"><div class="field-item even"><a href="/mathstat/news" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">News</a></div><div class="field-item odd"><a href="/mathstat/seminars-announce" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">Seminars</a></div><div class="field-item even"><a href="/mathstat/seminars/colloquium" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">Department Colloquium</a></div></div></div>Fri, 02 Oct 2020 20:56:46 +0000cowellj626 at https://www.queensu.ca/mathstatDepartment Colloquium - Abdalrazzaq Zalloum (Queen's)
https://www.queensu.ca/mathstat/department-colloquium-abdalrazzaq-zalloum-queens
<div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even" property="content:encoded"><div class="tex2jax"><h2>Department Colloquium</h2>
<hr style="height:1px;border:none;color:lightgrey;background-color:lightgrey;" /><div class="image-right">
<p><a href="/mathstat/sites/webpublish.queensu.ca.mastwww/files/images/news_and_seminars/colloquium/sept_25_2020.jpg"><img alt="Abdalrazzaq Zalloum (Queen's University)" src="/mastwww/sites/webpublish.queensu.ca.mastwww/files/images/news_and_seminars/colloquium/sept_25_2020.jpg" style="width: 450px; height: 370px;" /></a></p>
</div>
<h3>Friday, September 25th, 2020</h3>
<p><strong>Time:</strong> 2:30 p.m. <strong>Place:</strong> Online (via Zoom)</p>
<p><strong>Speaker:</strong> Abdalrazzaq Zalloum (Queen's University)</p>
<p><strong>Title:</strong> Negative curvature in geometric group theory.</p>
<p><strong>Abstract: </strong> Geometric group theory studies the interplay between the algebraic/combinatorial properties of infinite groups and the geometries of the spaces on which they act. A naive example of this phenomena is the following theorem: "An infinite group is free if and only if it admits a free action on some tree". In the previous theorem, the geometric property of the tree containing no loops informed the algebraic/combinatorial property of the group being free and vice versa; this is a theme in geometric group theory. A metric space $X$ is said to be hyperbolic if there exists a number $\delta$ such that for any geodesic triangle in $X$, the union of the {$\delta$-nbhd} of any two of its three sides contains the third, see the attached image. Group actions on hyperbolic spaces tend to be particularly informative. A fundamental (and almost defining) property of hyperbolic spaces is that infinite geodesics satisfy a \textit{local to global} property: to check whether an infinite path is a geodesic in $X$, you need only to check that in uniformly small windows. Given a nice action of an infinite group $G$ on a hyperbolic space $X$, Cannon showed that the local-to-global property of geodesics in $X$ is reflected in the combinatorial structure of $G$. In particular, he observed that the local-to-global property of $X$ is inherited by $G$ in the sense that all the combinatorial and growth information of the \textbf{infinite} group $G$ can be encoded using only a $\textbf{finite}$ amount of data: a finite graph. I will discuss recent work where we study groups acting on spaces satisfying a similar local-to-global property, and we will see the interplay between the geometric local-to-global properties of the space, and the combinatorial structure of the acting group. Some of the results I will discuss are joint with Cordes, Russell and Spriano.</p>
<p><strong>Abdalrazzaq Zalloum</strong> is a Coleman post-doctoral fellow within the Department of Mathematics and Statistics at Queen's University, working with Thomas Barthelmé and Francesco Cellarosi. He obtained his Ph.D. in Mathematics from the SUNY Buffalo in 2019. He is mainly interested in geometric group theory, which studies the interplay between the algebraic structures of groups and the geometries of the spaces on which they act.</p>
</div></div></div></div><div class="field field-name-field-tag field-type-taxonomy-term-reference field-label-above"><div class="field-label">Tags: </div><div class="field-items"><div class="field-item even"><a href="/mathstat/news" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">News</a></div><div class="field-item odd"><a href="/mathstat/seminars-announce" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">Seminars</a></div><div class="field-item even"><a href="/mathstat/seminars/colloquium" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">Department Colloquium</a></div></div></div>Fri, 25 Sep 2020 18:07:05 +0000cowellj625 at https://www.queensu.ca/mathstatDepartment Colloquium - Serdar Yuksel (Queen's University)
https://www.queensu.ca/mathstat/department-colloquium-serdar-yuksel-queens-university
<div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even" property="content:encoded"><div class="tex2jax"><h2>Department Colloquium</h2>
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<p><a href="/mathstat/sites/webpublish.queensu.ca.mastwww/files/images/news_and_seminars/colloquium/sept_11_2020.png"><img alt="Serdar Yuksel (Queen's University)" src="/mastwww/sites/webpublish.queensu.ca.mastwww/files/images/news_and_seminars/colloquium/sept_11_2020.png" style="width: 450px; height: 450px;" /></a></p>
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<h3>Friday, September 11th, 2020</h3>
<p><strong>Time:</strong> 2:30 p.m. <strong>Place:</strong> Online (via Zoom)</p>
<p><strong>Speaker:</strong> Serdar Yuksel (Queen's University)</p>
<p><strong>Title:</strong> Geometry of Information Structures, Strategic Measures and Associated Control Topologies.</p>
<p><strong>Abstract: </strong> In many areas of applied mathematics (including control theory, information theory, game theory) decentralization of information among several decision makers is unavoidable. Information and correlation structures determine who knows what information and how the decisions may be dependent leading to various problems on the geometry of correlation structures among decisions/controls. We define information structures, place various topologies on them, and study closedness and compactness properties on the (strategic) measures induced by decentralized control/decision policies under varying degrees of relaxations with regard to access to private or common randomness. Ultimately, we present existence and approximation results for optimal decision/control policies. We then discuss various upper and lower bounding techniques, through realizable and classically non-realizable (such as quantum correlations and non-signaling) convex relaxations and quantization. For each of these, we review or establish closedness and convexity properties and present a hierarchy of correlation structures. As a second main theme, we review or introduce various topologies on decision/control strategies defined independently from information structures, but for which information structures determine whether the topologies entail utility in arriving at existence, compactness, convexification or approximation results. These approaches, which we will term as the strategic measures approach (where the induced joint measure is considered) and the control topology approach (where a product space of individual control policy spaces is considered), lead to complementary results and solution methods in optimal stochastic control. (Joint work primarily with Prof. Naci Saldi, other collaborators will also be acknowledged).</p>
</div></div></div></div><div class="field field-name-field-tag field-type-taxonomy-term-reference field-label-above"><div class="field-label">Tags: </div><div class="field-items"><div class="field-item even"><a href="/mathstat/news" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">News</a></div><div class="field-item odd"><a href="/mathstat/seminars-announce" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">Seminars</a></div><div class="field-item even"><a href="/mathstat/seminars/colloquium" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">Department Colloquium</a></div></div></div>Fri, 11 Sep 2020 18:56:46 +0000cowellj621 at https://www.queensu.ca/mathstat