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  • The Nonlinear Hahn-Banach Theorem and Lipschitz Extensions - RIT on Applied Harmonic Analysis

    Speaker: Radu Balan (UMD) -

    When: Mon, February 26, 2018 - 3:00pm
    Where: Kirwan Hall 1308
  • Towards a Free Boundary Problem - RIT on Applied PDE

    Speaker: Konstantina Trivisa (University of Maryland) -

    When: Mon, February 26, 2018 - 3:00pm
    Where: Kirwan Hall 1311

    View Abstract

    Abstract: http://www.terpconnect.umd.edu/~lvrmr/2017-2018-S/Classes/RIT.shtml
  • Geometry of weighted Riemannian manifolds - Geometry-Topology

    Speaker: William Wylie (Syracuse University) - http://asfaculty.syr.edu/pages/math/wylie-william.html

    When: Mon, February 26, 2018 - 3:15pm
    Where: Kirwan Hall 3206

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    Abstract: A weighted Riemannian manifold is simply a Riemannian manifold equipped with a (variable) density function. For example, a surface with a positive function that describes the density of the material that makes up the surface. In this talk we'll discuss a new geometric approach to weighted Riemannian manifolds that takes a natural torsion free connection as the fundamental object of study. This approach gives new comparison results that are valid under weaker Ricci curvature assumptions than have previously been considered in the literature, and also leads to novel rigidity phenomena. Time permitting, we'll also discuss how the connection leads to a theory of sectional curvature bounds for weighted Riemannian manifolds.
  • The set of quantum correlations is not closed - RIT on Quantum Information

    Speaker: Brad Lackey (University of Maryland) - http://www.umiacs.umd.edu/~bclackey

    When: Mon, February 26, 2018 - 4:15pm
    Where: Atlantic 3100A

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    Abstract: We review Slofstra's construction of a family of nonlocal games that cannot be won with certainty using any finite-dimensional quantum strategy, however can be played perfectly in the limit of such strategies. The key methodology is to link a perfect strategy for such a game to a finite-dimensional representation of a specific finitely-presented group constructed from the game. Reference: Slofstra, arXiv:1703.08618.
  • Model Theory Reading Seminar - Student Logic Seminar

    Speaker: TBA () -

    When: Tue, February 27, 2018 - 2:00pm
    Where: Kirwan Hall 1311

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    Abstract: We continue our reading of "Regularity lemmas for distal structures"
  • A Coupling Lemma for Dispersive Billiards - Student Dynamics

    Speaker: Jing Zhou (UMD) -

    When: Tue, February 27, 2018 - 3:15pm
    Where: Kirwan Hall 1310
  • TBA - Logic

    Speaker: Gabriel Conant (University of Notre Dame) -

    When: Tue, February 27, 2018 - 3:30pm
    Where: Kirwan Hall 1311
  • The Infinitesimal Lifting Property - Student Algebraic Geometry Seminar

    Speaker: Daniel Kaufman (UMD) -

    When: Tue, February 27, 2018 - 3:30pm
    Where: Math 0104
  • Gromov's invariant - Student Geometry and Topology

    Speaker: S. Gilles (UMD) -

    When: Wed, February 28, 2018 - 1:00pm
    Where: Kirwan Hall 1310
  • The arithmetic of arithmetic Coxeter groups - Algebra-Number Theory

    Speaker: Marty Weissman (UCSC) - http://martyweissman.com/Abstract:  In the 1990s, John H. Conway developed a visual approach to the study of integer-valued binary quadratic forms.  His creation, the "topograph," sheds light on classical reduction theory, the solution of Pell-type equations, and allows tedious algebraic estimates to be simplified with straightforward geometric arguments.  The geometry of the topograph arises from a coincidence between the Coxeter group of type (3, infinity) and the group PGL(2,Z).  From this perspective, Conway's topograph is the first in a series of applications arising from coincidences between Coxeter groups and arithmetic groups.  In this talk, I will survey Conway's results and generalizations arising from arithmetic hyperbolic Coxeter groups.

    When: Wed, February 28, 2018 - 2:00pm
    Where: Kirwan Hall 1311

    View Abstract

    Abstract:  In the 1990s, John H. Conway developed a visual approach to the study of integer-valued binary quadratic forms.  His creation, the "topograph," sheds light on classical reduction theory, the solution of Pell-type equations, and allows tedious algebraic estimates to be simplified with straightforward geometric arguments.  The geometry of the topograph arises from a coincidence between the Coxeter group of type (3, infinity) and the group PGL(2,Z).  From this perspective, Conway's topograph is the first in a series of applications arising from coincidences between Coxeter groups and arithmetic groups.  In this talk, I will survey Conway's results and generalizations arising from arithmetic hyperbolic Coxeter groups.
  • Inference of variable population sizes from genomic sequence data using tree-length based Hidden Markov Models - CSCAMM

    Speaker: Prof. Alexey Miroshnikov (Mathematics Department, University of California at Los Angeles) - https://www.math.ucla.edu/~amiroshn/

    When: Wed, February 28, 2018 - 2:00pm
    Where: CSIC 4122

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    Abstract: Studying the demographic histories of humans or other species and understanding their effects on contemporary genetic variability is one of the central tasks of population genetics. In recent years, a number of methods have been developed to infer demographic histories, especially historical population size changes, from genomic sequence data. Coalescent Hidden Markov Models have proven to be particularly useful for this type of inference. Due to the Markovian structure of Coalescent Hidden Markov Models, an essential building block is the joint distribution of local genealogies, or statistics of these genealogies, in populations of variable size. This joint distribution of local genealogies has received little attention in the literature, especially under variable population size. In this talk, we present a novel method to compute the joint distribution of the total length of the genealogical trees at two linked loci for samples of arbitrary size. We show that the joint distribution can be obtained by solving a system of hyperbolic PDEs and present a numerical algorithm that can be used to efficiently and accurately solve the system and compute this distribution. Our flexible method can be straightforwardly extended to other statistics and structured populations. This is a joint work with Matthias Steinrucken (UChicago).
  • Economic inequality from a statistical physics point of view - Applied Dynamics

    Speaker: Victor Yakovenko - University of Maryland Department of Physics

    When: Thu, March 1, 2018 - 12:30pm
    Where: ERF 1027

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    Abstract: Inequality is an important and seemingly inevitable aspect of the human society. Various manifestations of inequality can be derived from the concept of entropy in statistical physics. In a stylized model of monetary economy, with a constrained money supply implicitly reflecting constrained resources, the probability distribution of money among the agents converges to the exponential Boltzmann-Gibbs law due to entropy maximization. Our empirical data analysis [1] shows that income distributions in the USA, European Union, and other countries exhibit a well-defined two-class structure. The majority of the population (about 97%) belongs to the lower class characterized by the exponential ("thermal") distribution. The upper class (about 3% of the population) is characterized by the Pareto power-law ("superthermal") distribution, and its share of the total income expands and contracts dramatically during booms and busts in financial markets. Interestingly, the same equations can be also applied to heavy-ion collisions [2]. Globally, energy consumption (and CO2 emissions) per capita around the world shows decreasing inequality in the last 30 years and convergence toward the exponential probability distribution, as expected from the maximal entropy principle. In agreement with our prediction [3], a saturation of the global Gini coefficient for energy consumption at 0.5 is observed for the most recent years. All papers are available at http://physics.umd.edu/~yakovenk/econophysics/.
    [1] Yong Tao et al., "Exponential structure of income inequality: evidence from 67 countries", Journal of Economic Interaction and Coordination (2017) http://doi.org/10.1007/s11403-017-0211-6 http://arxiv.org/abs/1612.01624
    [2] Xuejiao Yin et al., "A new two-component model for hadron production in heavy-ion collisions", Advances in High Energy Physics (2017) 6708581, http://doi.org/10.1155/2017/6708581
    [3] S. Lawrence, Q. Liu, and V. M. Yakovenko, "Global inequality in energy consumption from 1980 to 2010", Entropy 15, 5565 (2013), http://dx.doi.org/10.3390/e15125565
  • Families of periodic paths on the pentagon - Dynamics

    Speaker: Diana Davis (Swarthmore College) - http://www.swarthmore.edu/NatSci/ddavis3/Abstract: There are infinite "families" of periodic paths on the pentagon, whose members all have a similar appearance but get more and more complicated. I'll show some beautiful examples of these families, and explain how we use the group structure on the set of periodic directions to obtain them.

    When: Thu, March 1, 2018 - 2:00pm
    Where: Kirwan Hall 1311

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    Abstract: There are infinite "families" of periodic paths on the pentagon, whose members all have a similar appearance but get more and more complicated. I'll show some beautiful examples of these families, and explain how we use the group structure on the set of periodic directions to obtain them.
  • Sticky particles and the Euler-Poisson equations - PDE-Applied Math

    Speaker: Ryan Hynd (U-Penn) - https://web.sas.upenn.edu/rhynd/

    When: Thu, March 1, 2018 - 3:30pm
    Where: Kirwan Hall 3206

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    Abstract: We will consider the dynamics of a finite number of particles that interact pairwise and undergo perfectly inelastic collisions.
    Such physical systems conserve mass and momentum and satisfy the Euler-Poisson equations. In one spatial dimension, we will show
    how to derive an extra entropy estimate which allows us to characterize the limit as the number of particles tends to infinity.
  • Hitchin notes section 4 - RIT on Geometry and Physics

    Speaker: Ian Teixeira and Matthew Yu -

    When: Thu, March 1, 2018 - 3:30pm
    Where: Physics Bldg 1117

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    Abstract: We will continue going through Nigel Hitchin's Lectures on Generalized Geometry, arXiv:1008.0973. The topic this time will be generalized Kaehler manifolds.