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Science Division Calendar
Mathematics Colloquium: Liz Vivas (Purdue University), "Dynamics of homomorphic selfmaps near a fixed point"
Feb 14, 2013
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NA 6113
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Math Colloquium: Partha Sarathi Dey (NYU), Energy Landscape for `large average' Gaussian submatrices.
Feb 19, 2013
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NA 6113
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Math Colloquium: Alexandra Chronopoulou (UCSB), Statistical Inference for fractional SDEs and applications
Feb 21, 2013
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NA 6113
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Math Colloqium: Sergiy Merenkov (UIUC), "Quasisymmetries of Sierpinski carpets"
Feb 26, 2013
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NAC 6/113
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Mathematics Colloquium: Edson De Faria (University of Sao Paulo), "On Sloane's persistence problem"
Sep 19, 2013
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NAC 6113
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Abstract: We investigate the socalled persistence problem of Sloane, exploiting connections with the dynamics of circle maps and the ergodic theory of $\mathbb{Z}^d$ actions. We also formulate a conjecture, concerning the asymptotic distribution of digits in long products of primes chosen from a given finite set, whose truth would in particular solve the persistence problem. We provide computational evidence and an heuristic argument in favor of our conjecture. Such heuristics can be thought in terms of a simple model in statistical mechanics. This talk is based on joint work with Charles Tresser (IBM).
Mathematics Colloquium: Omer Offen (TechnionIsrael Institute of Technology), "Lfunctions and converse theorems"
Oct 03, 2013
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This talk will survey the notion of an automorphic Lfunction starting with the Riemann zeta function. We will discuss characterizations of L functions via converse theorems and analogues in the local theory.
Mathematics Colloquium: Renato Bettiol (University of Notre Dame), "Strong positive sectional curvature"
Oct 24, 2013
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Compact Riemannian manifolds with positive sectional curvature are very special objects that have been studied since the beginning of Riemannian geometry. Nevertheless, there are currently very few known examples and many conjectures regarding these objects remain elusive. A much stronger notion is that of manifolds with positive curvature operator, which have been completely classified through the use of Ricci flow. In this talk, I will describe an intermediate notion between the above two, that has not received much attention but essentially dates back to the work of Thorpe in the early 70's. The interest in this class arises from trying to understand the "gap" between the classes of manifolds with positive curvature operator and positive sectional curvature, with the hope to better understand the latter. This is joint work with R. Mendes (Notre Dame).
Mathematics Colloquium: Bart Van Steirteghem (Medgar Evers College),"Multiplying functions on affine spherical varieties"
Oct 31, 2013
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Spherical varieties form a remarkable class of algebraic varieties equipped with an action of a complex reductive group G. They include toric, flag and symmetric varieties. A natural invariant of an affine spherical variety X is the set S(X) of irreducible representations of G that occur in the coordinate ring O(X) of X. This talk will discuss the following question: given S(X), what are the possible multiplication laws on O(X)?
Mathematics Colloquium: Ali Altug (Columbia University), "Beyond Endoscopy via the Trace Formula"
Nov 07, 2013
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NAC 6113
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In his recent paper,“Beyond Endoscopy”, Langlands proposed an approach to (ultimately) attack the general functoriality conjectures by means of the trace formula. For a (reductive algebraic) group G over a global field F and a representation ρ : ^{L}G → GL(V), the strategy, among other things, aims at detecting those automorphic representations of G for which the Lfunction, L(s,π,ρ), has a pole at s = 1. The method suggested using the trace formula together with an averaging process to capture these poles. In this talk we will start by recalling the functoriality conjectures and briefly describe the method suggested by Langlands. Then, specializing on the group GL(2) we will discuss some recent work on Beyond Endoscopy. More precisely, we will discuss the elliptic part of the trace formula and the analytic problems caused by the volumes of tori, singularities of orbital integrals and the nontempered terms. We will then describe how one can use an approximate functional equation in the trace formula to rewrite the elliptic part which resolves these issues. Finally, we will talk about applications of the resulting formula.
Mathematics Colloquium: Christina Sormani (Lehman College and CUNY Graduate Center), "Tetrahedra, Rectifiability and the GromovHausdorff Convergence of Metric Spaces"
Nov 14, 2013
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We will begin with a review of the GromovHausdorff distance between metric spaces: a notion which is fundamental in both Geometric Analysis and Group Theory. Also fundamental to Geometric Analysis is the notion of Hausdorff measure and countably $H^m$ rectifiable metric spaces (a class of metric spaces upon which one can define differentiation almost everywhere). Even more smooth are the Riemannian manifolds where one can define second derivatives and study partial differential equations. Gromov's Compactness Theorem states that sequences of metric spaces with a uniform upper bound on diameter and on the numbers of disjoint balls contained in the space, have a converging subsequence. One can apply his theorem to study sequences of Riemannian manifolds; however, the limits may only be metric spaces, not Riemannian manifolds and not even countably $H^m$ rectifiable. Today we present a new theorem in which a sequence of Riemannian manifolds is assumed to have an upper bound on diameter and on volume and also a uniform condition on tetrahedra, and one finds a subsequence converges in the GromovHausdorff sense to a countably $H^m$ rectifiable metric space. We do not present the proof but it involves tools from Geometric Measure Theory, work of AmbrosioKirchheim dating to 2000, as well as the notion of Intrinsic Flat convergence developed in joint work with Stefan Wenger in 2011.
Mathematics Colloquium: Christopher Staecker (Fairfield University), "The rotation number for maps on graphs"
Nov 21, 2013
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While studying the precession of planetary orbits, Poincare introduced the rotation number for a homeomorphism of a circle. This is the "average" angle that points traverse under the homeomorphism, and has become a fundamental tool in the theory of dynamics on the circle. The basic concept has been extended to maps on the annulus and torus, and some other settings. We will discuss a generalization of the rotation number to maps of finite graphs which has been developed in joint work with Chris Bernhardt. Using the fundamental group and some basic covering space theory we describe a rotation element which obeys natural properties analogous to the classical rotation number. This invariant naturally takes the form of an element of a "free group with noninteger exponents". We will discuss recent results as well as some new work in progress.
Mathematics Colloquium: Karen Taylor (Bronx Community College), "Fourier Coefficients of Hyperbolic Modular Forms"
Dec 05, 2013
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In the study of modular forms two constructions based on translation invariance arise: One is the fourier expansion of a modular form, the other is the Petersson Poincare series. In this talk we explore the analogous series based on invariance under a hyperbolic element of the modular group. This work initiated with Petersson (1941) who showed, in addition to the parabolic expansion, that modular forms have elliptic and hyperbolic expansions. We particularly highlight the algebra and geometry of real quadratic fields that arise in finding fourier coefficients of hyperbolic Eisenstein series. This is a preliminary report on joint work with Cormac O'Sullivan.
Mathematics Colloquium: Xavier Bresson (University of Lausanne), Total Variation Data Analysis  A Nonlinear Spectral Framework for Machine Learning
Feb 13, 2014
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Mathematics Colloquium: Shirshendu Chatterjee (NYU), Stochastic Spacial Models for some Naturally Occurring Phenomena
Feb 18, 2014
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Mathematics Colloquium: Sevak Mkrtchyan (Carnegie Mellon University), The dimer model on the hexagonal lattice
Feb 25, 2014
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TBA
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Mathematics Colloquium: Hautieng Wu (Stanford University), Alternating Projection, Ptychography and High Dimensional Phase Retrieval
Feb 26, 2014
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TBA
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Math Colloquium: Alex Lubotzky, "High dimensional expanders and Ramanujan complexes"
Sep 04, 2014
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NAC 6/113
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EAS Seminar: The melting of Greenland: Why does it matter and how does it sound?
Feb 13, 2014
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MR 107
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Professor Marco Tedesco will provide an overview on the largest island of the world: Greenland. In particular, he will show results from his previous expeditions concerning the dynamics of ice, the melting of the ice during summer and the presence of life on the ice sheet.
EAS Seminar: A Global Geography of Urban Greenhouse Gas Emissions
Mar 13, 2014
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MR 107
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Associate Professor Peter Marcotullio of the Department of Geography, Hunter College will describe global urban greenhouse gas emissions by region and sector, and he will examine the distribution of emissions through the urbantorural gradient, and identify covariates of emission levels using the year 2000 as baseline year.
EAS Seminar: Landatmosphere exchanges a critical component of Earth’s energy, carbon, and water budgets
Feb 27, 2014
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MR 107
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Dr. David M. Sumner of the USGS Florida Water Science Center will provide an overview of landatmosphere exchanges as a a critical component of Earth’s energy, carbon, and water budgets. Exchanges of energy and mass between the landscape and the atmosphere can impact the climate, the hydrologic budget, the ecosystem, and even topography. The USGS Florida Water Science Center has embarked on an effort to monitor these environmental exchanges using a combination of field and satellitebased means.
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