2015 Satter Prize
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CURRENT EVENTS BULLETIN Friday, January 8, 2016, 1:00 PM to 5:00 PM Room 4C-3 Washington State Convention Center Joint Mathematics Meetings, Seattle, WA
A MERICAN M ATHEMATICAL S OCIETY CURRENT EVENTS BULLETIN Friday, January 8, 2016, 1:00 PM to 5:00 PM Room 4C-3 Washington State Convention Center Joint Mathematics Meetings, Seattle, WA 1:00 PM Carina Curto, Pennsylvania State University What can topology tell us about the neural code? Surprising new applications of what used to be thought of as “pure” mathematics. 2:00 PM Yuval Peres, Microsoft Research and University of California, Berkeley, and Lionel Levine, Cornell University Laplacian growth, sandpiles and scaling limits Striking large-scale structure arising from simple cellular automata. 3:00 PM Timothy Gowers, Cambridge University Probabilistic combinatorics and the recent work of Peter Keevash The major existence conjecture for combinatorial designs has been proven! 4:00 PM Amie Wilkinson, University of Chicago What are Lyapunov exponents, and why are they interesting? A basic tool in understanding the predictability of physical systems, explained. Organized by David Eisenbud, Mathematical Sciences Research Institute Introduction to the Current Events Bulletin Will the Riemann Hypothesis be proved this week? What is the Geometric Langlands Conjecture about? How could you best exploit a stream of data flowing by too fast to capture? I think we mathematicians are provoked to ask such questions by our sense that underneath the vastness of mathematics is a fundamental unity allowing us to look into many different corners -- though we couldn't possibly work in all of them. I love the idea of having an expert explain such things to me in a brief, accessible way. And I, like most of us, love common-room gossip. -
What Are Lyapunov Exponents, and Why Are They Interesting?
BULLETIN (New Series) OF THE AMERICAN MATHEMATICAL SOCIETY Volume 54, Number 1, January 2017, Pages 79–105 http://dx.doi.org/10.1090/bull/1552 Article electronically published on September 6, 2016 WHAT ARE LYAPUNOV EXPONENTS, AND WHY ARE THEY INTERESTING? AMIE WILKINSON Introduction At the 2014 International Congress of Mathematicians in Seoul, South Korea, Franco-Brazilian mathematician Artur Avila was awarded the Fields Medal for “his profound contributions to dynamical systems theory, which have changed the face of the field, using the powerful idea of renormalization as a unifying principle.”1 Although it is not explicitly mentioned in this citation, there is a second unify- ing concept in Avila’s work that is closely tied with renormalization: Lyapunov (or characteristic) exponents. Lyapunov exponents play a key role in three areas of Avila’s research: smooth ergodic theory, billiards and translation surfaces, and the spectral theory of 1-dimensional Schr¨odinger operators. Here we take the op- portunity to explore these areas and reveal some underlying themes connecting exponents, chaotic dynamics and renormalization. But first, what are Lyapunov exponents? Let’s begin by viewing them in one of their natural habitats: the iterated barycentric subdivision of a triangle. When the midpoint of each side of a triangle is connected to its opposite vertex by a line segment, the three resulting segments meet in a point in the interior of the triangle. The barycentric subdivision of a triangle is the collection of 6 smaller triangles determined by these segments and the edges of the original triangle: Figure 1. Barycentric subdivision. Received by the editors August 2, 2016. -
Apollonian Circle Packings: Dynamics and Number Theory
APOLLONIAN CIRCLE PACKINGS: DYNAMICS AND NUMBER THEORY HEE OH Abstract. We give an overview of various counting problems for Apol- lonian circle packings, which turn out to be related to problems in dy- namics and number theory for thin groups. This survey article is an expanded version of my lecture notes prepared for the 13th Takagi lec- tures given at RIMS, Kyoto in the fall of 2013. Contents 1. Counting problems for Apollonian circle packings 1 2. Hidden symmetries and Orbital counting problem 7 3. Counting, Mixing, and the Bowen-Margulis-Sullivan measure 9 4. Integral Apollonian circle packings 15 5. Expanders and Sieve 19 References 25 1. Counting problems for Apollonian circle packings An Apollonian circle packing is one of the most of beautiful circle packings whose construction can be described in a very simple manner based on an old theorem of Apollonius of Perga: Theorem 1.1 (Apollonius of Perga, 262-190 BC). Given 3 mutually tangent circles in the plane, there exist exactly two circles tangent to all three. Figure 1. Pictorial proof of the Apollonius theorem 1 2 HEE OH Figure 2. Possible configurations of four mutually tangent circles Proof. We give a modern proof, using the linear fractional transformations ^ of PSL2(C) on the extended complex plane C = C [ f1g, known as M¨obius transformations: a b az + b (z) = ; c d cz + d where a; b; c; d 2 C with ad − bc = 1 and z 2 C [ f1g. As is well known, a M¨obiustransformation maps circles in C^ to circles in C^, preserving angles between them. -
Read Press Release
The Work of Artur Avila Artur Avila has made outstanding contributions to dynamical systems, analysis, and other areas, in many cases proving decisive results that solved long-standing open problems. A native of Brazil who spends part of his time there and part in France, he combines the strong mathematical cultures and traditions of both countries. Nearly all his work has been done through collaborations with some 30 mathematicians around the world. To these collaborations Avila brings formidable technical power, the ingenuity and tenacity of a master problem-solver, and an unerring sense for deep and significant questions. Avila's achievements are many and span a broad range of topics; here we focus on only a few highlights. One of his early significant results closes a chapter on a long story that started in the 1970s. At that time, physicists, most notably Mitchell Feigenbaum, began trying to understand how chaos can arise out of very simple systems. Some of the systems they looked at were based on iterating a mathematical rule such as 3x(1−x). Starting with a given point, one can watch the trajectory of the point under repeated applications of the rule; one can think of the rule as moving the starting point around over time. For some maps, the trajectories eventually settle into stable orbits, while for other maps the trajectories become chaotic. Out of the drive to understand such phenomena grew the subject of discrete dynamical systems, to which scores of mathematicians contributed in the ensuing decades. Among the central aims was to develop ways to predict long-time behavior. -
Arithmetic Sums of Nearly Affine Cantor Sets
UNIVERSITY OF CALIFORNIA, IRVINE Arithmetic Sums of Nearly Affine Cantor Sets DISSERTATION submitted in partial satisfaction of the requirements for the degree of DOCTOR OF PHILOSOPHY in Mathematics by Scott Northrup Dissertation Committee: Associate Professor Anton Gorodetski, Chair Professor Svetlana Jitomirskaya Associate Professor Germ´anA. Enciso 2015 c 2015 Scott Northrup DEDICATION To Cynthia and Max. ii TABLE OF CONTENTS Page LIST OF FIGURES iv ACKNOWLEDGMENTS v CURRICULUM VITAE vi ABSTRACT OF THE DISSERTATION vii Introduction 1 1 Outline 7 1.1 Statement of the Results . 7 1.2 Organization of the Thesis . 9 2 Cantor Sets 11 2.1 Dynamically Defined Cantor Sets . 11 2.2 Dimension Theory . 15 2.3 The Palis Conjecture . 18 2.4 Middle-α Cantor Sets . 19 2.5 Homogeneous Self-Similar Cantor Sets . 21 2.6 A Positive Answer to the Palis Conjecture . 22 2.7 The dimH C1 + dimH C2 < 1 Case . 23 3 Results for Nearly Affine Cantor Sets 26 3.1 Absolute Continuity of Convolutions . 26 3.2 Theorem 1.1 . 27 3.3 Construction of Measures for K and Cλ ..................... 28 3.4 Verifying the Conditions of Proposition 3.1 . 32 3.5 Corollaries . 41 4 Open Questions 42 Bibliography 44 A Proof of Proposition 3.1 51 iii LIST OF FIGURES Page 1 The horseshoe map; ' contracts the square horizontally and expands it verti- cally, before folding it back onto itself. The set of points invariant under this map will form a hyperbolic set, called Smale's Horseshoe............ 4 2.1 The Horseshoe map, again . 12 2.2 A few iterations of the Stable Manifold . -
SPATIAL STATISTICS of APOLLONIAN GASKETS 1. Introduction Apollonian Gaskets, Named After the Ancient Greek Mathematician, Apollo
SPATIAL STATISTICS OF APOLLONIAN GASKETS WEIRU CHEN, MO JIAO, CALVIN KESSLER, AMITA MALIK, AND XIN ZHANG Abstract. Apollonian gaskets are formed by repeatedly filling the interstices between four mutually tangent circles with further tangent circles. We experimentally study the nearest neighbor spacing, pair correlation, and electrostatic energy of centers of circles from Apol- lonian gaskets. Even though the centers of these circles are not uniformly distributed in any `ambient' space, after proper normalization, all these statistics seem to exhibit some interesting limiting behaviors. 1. introduction Apollonian gaskets, named after the ancient Greek mathematician, Apollonius of Perga (200 BC), are fractal sets obtained by starting from three mutually tangent circles and iter- atively inscribing new circles in the curvilinear triangular gaps. Over the last decade, there has been a resurgent interest in the study of Apollonian gaskets. Due to its rich mathematical structure, this topic has attracted attention of experts from various fields including number theory, homogeneous dynamics, group theory, and as a consequent, significant results have been obtained. Figure 1. Construction of an Apollonian gasket For example, it has been known since Soddy [23] that there exist Apollonian gaskets with all circles having integer curvatures (reciprocal of radii). This is due to the fact that the curvatures from any four mutually tangent circles satisfy a quadratic equation (see Figure 2). Inspired by [12], [10], and [7], Bourgain and Kontorovich used the circle method to prove a fascinating result that for any primitive integral (integer curvatures with gcd 1) Apollonian gasket, almost every integer in certain congruence classes modulo 24 is a curvature of some circle in the gasket. -
Arxiv:1609.08664V2 [Math-Ph] 9 Dec 2017 Yhftde N[ in Hofstadter by Ae[ Case Atrpern Sntitne O Publication
UNIVERSAL HIERARCHICAL STRUCTURE OF QUASIPERIODIC EIGENFUNCTIONS SVETLANA JITOMIRSKAYA AND WENCAI LIU Abstract. We determine exact exponential asymptotics of eigenfunctions and of corre- sponding transfer matrices of the almost Mathieu operators for all frequencies in the lo- calization regime. This uncovers a universal structure in their behavior, governed by the continued fraction expansion of the frequency, explaining some predictions in physics liter- ature. In addition it proves the arithmetic version of the frequency transition conjecture. Finally, it leads to an explicit description of several non-regularity phenomena in the cor- responding non-uniformly hyperbolic cocycles, which is also of interest as both the first natural example of some of those phenomena and, more generally, the first non-artificial model where non-regularity can be explicitly studied. 1. Introduction A very captivating question and a longstanding theoretical challenge in solid state physics is to determine/understand the hierarchical structure of spectral features of operators describ- ing 2D Bloch electrons in perpendicular magnetic fields, as related to the continued fraction expansion of the magnetic flux. Such structure was first predicted in the work of Azbel in 1964 [11]. It was numerically confirmed through the famous butterfly plot and further argued for by Hofstadter in [29], for the spectrum of the almost Mathieu operator. This was even before this model was linked to the integer quantum Hall effect [48] and other important phenom- ena. Mathematically, it is known that the spectrum is a Cantor set for all irrational fluxes [5], and moreover, even all gaps predicted by the gap labeling are open in the non-critical case [6, 8]. -
2014 AMS Elections---Biographies of Candidates
Biographies of Candidates 2014 Biographical information about the candidates has been supplied and verified by the candidates. Candidates have had the opportunity to make a statement of not more than 200 words (400 words for presidential candidates) on any subject matter without restriction and to list up to five of their research papers. Candidates have had the opportunity to supply a photograph to accompany their biographical information. Candidates with an asterisk (*) beside their names were nominated in response to a petition. Abbreviations: American Association for the Advancement of Science (AAAS); American Mathematical Society (AMS); American Statistical Association (ASA); Association for Computing Machinery (ACM); Association for Symbolic Logic (ASL); Association for Women in Mathematics (AWM); Canadian Mathematical Society, Société Mathématique du Canada (CMS); Conference Board of the Mathematical Sciences (CBMS); Institute for Advanced Study (IAS), Insti- tute of Mathematical Statistics (IMS); International Mathematical Union (IMU); London Mathematical Society (LMS); Mathematical Association of America (MAA); Mathematical Sciences Research Institute (MSRI); National Academy of Sciences (NAS); National Academy of Sciences/National Research Council (NAS/NRC); National Aeronautics and Space Administration (NASA); National Council of Teachers of Mathematics (NCTM); National Science Foundation (NSF); Society for Industrial and Applied Mathematics (SIAM). Vice President Mathematics, Princeton, 2004–2010; Dean of Natural Sci- ences, Duke, 2010–2012; Director, Information Initiative, Robert Calderbank Duke, 2012–present. Boards: Institute for Mathematics Professor of Mathematics, Direc- and Applications, Board of Governors, 1996–1999; NSF tor of the Information Initiative, Committee of Visitors, Division of Mathematical Sciences, Duke University (iiD). 2001; American Institute of Mathematics, Scientific Advi- Born: December 28, 1954, Bridg- sory Board, 2006–present; Institute for Pure and Applied water, Somerset, UK. -
Origin of Exponential Growth in Nonlinear Reaction Networks
Origin of exponential growth in nonlinear reaction networks Wei-Hsiang Lina,b,c,d,e,1, Edo Kussellf,g, Lai-Sang Youngh,i,j, and Christine Jacobs-Wagnera,b,c,d,e,k,1 aMicrobial Science Institute, Yale University, West Haven, CT 06516; bDepartment of Molecular, Cellular and Developmental Biology, Yale University, New Haven, CT 06511; cHoward Hughes Medical Institute, Yale University, New Haven, CT 06510; dDepartment of Biology, Stanford University, Palo Alto, CA 94305; eChemistry, Engineering & Medicine for Human Health (ChEM-H) Institute, Stanford University, Palo Alto, CA 94305; fCenter of Genomics and Systems Biology, Department of Biology, New York University, New York, NY 10003; gDepartment of Physics, New York University, New York, NY 10003; hCourant Institute of Mathematical Science, New York University, New York, NY 10012; iSchool of Mathematics, Institute for Advanced Study, Princeton, NJ 08540; jSchool of Natural Sciences, Institute for Advanced Study, Princeton, NJ 08540; and kDepartment of Microbial Pathogenesis, Yale School of Medicine, New Haven, CT 06510 Contributed by Christine Jacobs-Wagner, September 10, 2020 (sent for review June 24, 2020; reviewed by Jeff Gore and Ned S. Wingreen) Exponentially growing systems are prevalent in nature, spanning For example, the levels of metabolites and proteins can oscillate all scales from biochemical reaction networks in single cells to food during cell growth (13–15). The abundance of species in eco- webs of ecosystems. How exponential growth emerges in nonlin- systems can also oscillate (6) or exhibit nonperiodic fluctuations ear systems is mathematically unclear. Here, we describe a general (7). Yet, the biomass of these systems increases exponentially theoretical framework that reveals underlying principles of long- (6, 7, 16). -
Uniform Exponential Mixing and Resonance Free Regions for Convex Cocompact Congruence Subgroups of Sl2(Z)
UNIFORM EXPONENTIAL MIXING AND RESONANCE FREE REGIONS FOR CONVEX COCOMPACT CONGRUENCE SUBGROUPS OF SL2(Z) HEE OH AND DALE WINTER Abstract. Let Γ < SL2(Z) be a non-elementary finitely generated sub- group and Γ(q) be its congruence subgroup of level q for each q 2 N. We obtain an asymptotic formula for the matrix coefficients of 2 L (Γ(q)n SL2(R)) with a uniform exponential error term for all square- free q with no small prime divisors. As an application we establish a uniform resonance-free half plane for the resolvent of the Laplacian on 2 Γ(q)nH over q as above. Our approach is to extend Dolgopyat's dynam- ical proof of exponential mixing of the geodesic flow uniformly over con- gruence covers, by establishing uniform spectral bounds for congruence transfer operators associated to the geodesic flow. One of the key ingre- dients is the `2-flattening lemma due to Bourgain-Gamburd-Sarnak. 1. Introduction 1.1. Uniform exponential mixing. Let G = SL2(R) and Γ be a non- elementary finitely generated subgroup of SL2(Z). We will assume that Γ contains the negative identity −e but no other torsion elements. In other words, Γ is the pre-image of a torsion-free subgroup of PSL2(Z) under the canonical projection SL2(Z) ! PSL2(Z). For each q ≥ 1, consider the congruence subgroup of Γ of level q: Γ(q) := fγ 2 Γ: γ ≡ e mod qg: For t 2 R, let et=2 0 a = : t 0 e−t=2 As is well known, the right translation action of at on ΓnG corresponds to the geodesic flow when we identify ΓnG with the unit tangent bundle of a 2 hyperbolic surface ΓnH . -
Lecture Notes in Physics
Lecture Notes in Physics Editorial Board R. Beig, Wien, Austria W. Beiglböck, Heidelberg, Germany W. Domcke, Garching, Germany B.-G. Englert, Singapore U. Frisch, Nice, France P. Hänggi, Augsburg, Germany G. Hasinger, Garching, Germany K. Hepp, Zürich, Switzerland W. Hillebrandt, Garching, Germany D. Imboden, Zürich, Switzerland R. L. Jaffe, Cambridge, MA, USA R. Lipowsky, Golm, Germany H. v. Löhneysen, Karlsruhe, Germany I. Ojima, Kyoto, Japan D. Sornette, Nice, France, and Zürich, Switzerland S. Theisen, Golm, Germany W. Weise, Garching, Germany J. Wess, München, Germany J. Zittartz, Köln, Germany The Lecture Notes in Physics The series Lecture Notes in Physics (LNP), founded in 1969, reports new developments in physics research and teaching – quickly and informally, but with a high quality and the explicit aim to summarize and communicate current knowledge in an accessible way. Books published in this series are conceived as bridging material between advanced grad- uate textbooks and the forefront of research to serve the following purposes: • to be a compact and modern up-to-date source of reference on a well-defined topic; • to serve as an accessible introduction to the field to postgraduate students and nonspe- cialist researchers from related areas; • to be a source of advanced teaching material for specialized seminars, courses and schools. Both monographs and multi-author volumes will be considered for publication. Edited volumes should, however, consist of a very limited number of contributions only. Pro- ceedings will not be considered for LNP. Volumes published in LNP are disseminated both in print and in electronic formats, the electronic archive is available at springerlink.com. -
Yuki Takahashi
Yuki Takahashi Contact Saitama University [email protected] Information Department of Mathematics http://www.math.uci.edu/~takahasy/ Research Dynamical Systems, Spectral Theory and Fractal Geometry. Interests Employment Department of Mathematics, Saitama University • Assistant Professor, October 2020 - present Department of Mathematics, Michigan State University • Visiting Assistant Professor, January 2020 - August 2020 (research mentor: I. Kachkovskiy) AIMR Mathematical Science Group, Tohoku University • Assistant Professor (non tenure-track), April 2019 - December 2019 (Chiba research group) Department of Mathematics, Bar-Ilan University • Postdoc, June 2017 - March 2019 (supervisor: B. Solomyak) Education Department of Mathematics, University of California, Irvine • Ph.D. in Mathematics, May 2017 (advisor: A. Gorodetski) Ph.D. Thesis: Sums and products of Cantor sets and separable two-dimensional quasicrystal models The University of Tokyo • M.S. in Mathematics, March 2012 Master's Thesis: Irregular solutions of the periodic discrete Toda lattice equation (in Japanese) • B.A. in Mathematics, March 2009 Grants Spring 2020 Leibniz Fellowship Grant (Mathematisches Forschungsinstitut Oberwolfach) Fall 2019 FY2019 WPI-AIMR Fusion Research (Microfluidic, energy, and spin devices with fractal space-filling geometries, together with H. Izuchi, H. Kai and K. Kizu) Winter 2018 Leibniz Fellowship Grant (declined) (Mathematisches Forschungsinstitut Oberwolfach) Fall 2017 Postdoctoral Fellowship Grant (Institut Mittag-Leffler, postdoctoral fellowship) Honors and Spring 2017 Dissertation Fellowship (UC Irvine, department fellowship) Awards Winter 2017 Department Fellowship (UC Irvine, department fellowship) Spring 2014 Connelly Award (UC Irvine, department award) Spring 2013 Euler Outstanding Promise as a Graduate Student Award (UC Irvine, department award) Papers (in 1. Y. Takahashi, On the invariant measures for Iterated Function Systems with in- preparation) verses.