# Faculty News Briefs

### September 2019

On 1 July 2019, Visiting Assistant Professor Noriyuki Hamada was cross-appointed as Assistant Professor at Hokkaido University in Japan. This is part of a collaboration between the Department of Mathematics and Statistics at UMass Amherst and the Global Station for Big Data and Cybersecurity (GSB) in Global Institution for Collaborative Research and Education (GI-CoRE) at Hokkaido University. With this appointment, Noriyuki stayed at GSB in July and August, and gave talks at several universities in Japan, including one given in the "2019 Summer International Symposium on Big-Data, Cybersecurity and IoT" at Hokkaido University.

In early June, Professors Rob Kusner and Alexei Oblomkov were at the ForschungsInstitutMath (FIM) of ETH Zurich. Rob was a guest of ETH Professor Tom Ilmanen, participating in the week-long FIM/ETH conference celebrating the 60th birthday of Professor Gerhard Huisken (Director of MFOberwolfach), and chairing its final session. Rob also spoke on "Willmore Stability and Conformal Rigidity of Minimal Surfaces in $S^n$" at the Lehigh Geometry & Topology Conference held 20-22 June.

[A new Faculty News Briefs editor will come aboard soon! Please see the Department News items above (brought to you by Rachel Aronow and Rob Kusner) in the meantime.]

### June 2019

During the last week of May, the Centre International de Rencontres Mathematiques (CIRM) in Luminy, France, hosted a workshop on variational methods in geometry. Professors Rob Kusner and Franz Pedit were members of the scientific committee, and they were also invited by the workshop organizers to deliver plenary lectures. Franz lectured on a new approach to understand the space of curves, and Rob lectured on the Willmore Stability of Minimal Surfaces in the n-Sphere, one [113] of three lectures (the other two were by Ernst Kuwert [111] and Melanie Rupflin [112]) from the workshop recorded and included in the CIRM Geometry playlist. Earlier in May, at TU Darmstadt, Rob lectured on the Willmore index of complete minimal surfaces in 3-space (a topic he began working on decades ago when he conceived his "minimax" sphere eversions, a video-clip of which begins his CIRM lecture), sharpening a result of Jonas Hirsch and Elena Mader-Baumdicker with whom he is collaborating to obtain the optimal results.

### March 2019

**Kudos to our undergrads!!!**

The 34th annual *Jacob-Cohen-Killam Mathematics Competition*, open to all frosh and sophomores at UMass, was held 20 March 2019. The first place winner is Patrick Lei, who was also a winner last year. Guanghao Wei and Sattwik Das took second and third place, while Shirui Cao and Risen Luan share fourth place. This year's competition was organized by Professor Jenia Tevelev, and it continues to be sponsored by alumni John Baillieul, James Francis and Roy Perdue.

Two of our senior undergrads, Stefan Grosser and Wilson (Yike) Wang, were selected for the top 15% "Outstanding Poster Awards" from among more than 400 posters presented at the MAA undergraduate research poster session of the 2019 Joint (AMS & MAA) Math Meetings in Baltimore. The posters were on two projects, "Determinant formulas for counting linear extensions of tree posets" and "The minimum permanent of doubly-stochastic matrices with restricted positions," in the field of combinatorics. Stefan worked with Jacob Matherne (former VAP, now a member of the School of Mathematics at the Institute for Advanced Study) and Assistant Professor Alejandro Morales; Wilson did a summer REU with Alejandro.

**And in other news...**

Associate Professor R. Inanc Baykur and his collaborator Osamu Saeki recently published an article Simplified broken Lefschetz fibrations and trisections of 4-manifolds in the *Proceedings of the National Academy of Sciences.*

Stathis Charalampidis spoke on "Peregrine solitons and gradient catastrophes in continuous and discrete NLS systems" at the 2019 Joint Mathematics Meetings in Baltimore. He gave 4 colloquia, all titled "Nonlinear waves: From optics to matter waves and beyond" at Cal Poly San Luis Obispo (8 February ), at San Jose State University (11 February), at Johns Hopkins (15 February), and at the New York Institute of Technology (26 February). Stathis will also speak about "Formation of extreme events in nonlinear Schrodinger (NLS) systems" in the *11th IMACS International Conference on Nonlinear Evolution Equations and Wave Phenomena: Computation and Theory* at the University of Georgia, Athens on 17 April 2019.

On 6 March 2019, Associate Professor Erin Conlon gave the University of Connecticut Department of Statistics seminar "Parallel Markov chain Monte Carlo for Bayesian Hierarchical Models with Big Data, in Two Stages."

Professor Rob Kusner co-authored (with Hugh Bray, Michael Eichmair, Ailana Fraser, LanHsuan Huang, Fernando Coda Marques, Chika Mese, Bill Minicozzi, Karen Uhlenbeck & S.T. Yau) and helped edit an invited scientific tribute The Mathematics of Richard Schoen that appeared in the December 2018 *Notices of the American Mathematical Society.* At the beginning of spring break, Rob visited the Institute for Advanced Study; and at the end of the break, he gave an hour-long talk "Willmore stability and conformal rigidity of minimal surfaces" at the AMS meeting in Auburn, 15-17 March 2019, in the same special session that our incoming Marshall H. Stone VAP, Rafael Montezuma Cabral, also spoke.

Professor Franz Pedit spent 15-22 December 2018 at the *SFBTR 109: Discerete Geometry and Dynamics* of TU-Berlin to collaborate on the constrution of piecewise smooth conformal and isometric immersions into 3-space. Franz was invited to the Tata Institute of Fundamental Research in Mumbai for the period 8-27 January 2019 to collaborate with Professors Indranil Biswas and Sebastian Heller on surface geometric aspects of Deligne-Hitchin moduli spaces. During 9-24 March, Pedit was invited back to *SFBTR 109*, pursuing various projects, including Hamiltonian flows on the space of immersions, and connections to the Novikov-Veselov and Davey-Stewartson hierarchies.

On 27 February 2019, Marshall H. Stone Visiting Assistant Professor Luca Schaffler gave a seminar talk at Washington University in St. Louis titled "Compactifications of an interesting family of K3 surfaces from 8 points in $P^1$".

Department Head and Professor Nathaniel Whitaker "got good quote" in last month's *New York Times* article For a Black Mathematician, What It’s Like to Be the ‘Only One’ !

On 8 March 2019, emeritus Professor Floyd Williams gave an invited colloquium talk titled "Ramanujan: A mini portrait of a super mathematical mind" at Western New England University (this was his third invitation to speak there).

### December 2018

During the weekend of 26-28 October, the *Knotted surfaces in 4-manifolds* conference was hosted at UMass Amherst with funding by the National Science Foundation. Organized by Professors R. Inanc Baykur, Weimin Chen, and Danny Ruberman (of Brandeis University), it drew a diverse crowd of over 50 researchers from across the country and around world who contributed to a productive weekend of lively presentations and discussions covering new advances and open questions in the world of smooth 4-manifold topology. Many presentations included applications of relatively new tools — for example, trisections, Gabai’s 4-dimensional light bulb theorem, and various flavors of Floer homology — illustrating their utility in helping understand fundamental questions about surfaces in 4-manifolds.

Visiting Assistant Professor Jeremiah Birrell spoke about "Uncertainty Quantification via Variational Principles and Functional Inequalities" during the *Functional Inequalities in Probability Workshop* at the University of Connecticut on 2 November. He also gave a talk titled "Langevin Equations in the Small-Mass Limit: Higher-Order Approximations, Phase-Space Homogenization, and Entropy Production" in the Northeast Probability Seminar at the Courant Institute of Mathematical Sciences on 16 November.

Professor Emeritus John Buonaccorsi presented a talk on "The Use (or Misuse) of External Validation Data" as part of a workshop *Methodological Issues in Measurement Error* held at the National Cancer Institute on 5-6 November. The workshop, attended by approximately 60 people throughout NIH/NCI, brought together experts in the field to overview outstanding issues and future directions, especially as they pertain to many of the large national surveys concerned with health effects.

On 18 September, Associate Professor Erin Conlon gave the Yale University Department of Biostatistics seminar "Parallel Markov Chain Monte Carlo Methods for Bayesian Analysis of Big Data."

Marshall H. Stone Visiting Assistant Professor Taryn Flock gave a plenary talk titled "On the nonlinear Brascamp-Lieb inequality" at the *3rd Annual Northeastern Analysis Meeting* held at SUNY-New Paltz, 19-21 October.

This fall Professor Rob Kusner was re-elected to the Board of Trustees of AMIAS – the Association of Members of the Institute for Advanced Study – and he participated in the IAS workshop on *Mean Curvature in Geometric Analysis* the week of 5-9 November. He also lectured on "Willmore Stability, Area Index, and Conformal Rigidity of Minimal Surfaces in $S^n$" at Penn's Geometry and Topology seminar 13 November.

The week of 8-12 October, Professor Franz Pedit gave a plenary talk titled ``Commuting Hamiltonian flows on curves in real space forms" at the * International Conference on Discretization in Geometry and Dynamics* at Hotel Doellnsee-Schorfheide, Germany.

Marshall H. Stone Visiting Assistant Professor Luca Schaffler had the paper "Equations for point configurations to lie on a rational normal curve" (joint with A. Caminata, N. Giansiracusa, and H.-B. Moon) published by *Advances in Mathematics.* On 14 November he gave a talk about it in the Algebra Seminar at the University of Connecticut.

On 18 October, Professor Emeritus Floyd Williams was invited to speak at Western New England University on the occasion of celebration of 30 years of their Math.Center: a center for the mentoring and tutoring of students. Floyd spoke on "Cultivating mentorship in the unitary university: fruits from its garden." The event, which was programmed from noon to 6:30, was sponsored by the Math.Center, the Diversity Task Force, the Office of the Provost, and the College of Arts and Sciences. That gave Floyd the opportunity to chat with many of the students, faculty, staff, and deans.

We regret to report the passing of Professor Emeritus Samuel S. Holland, Jr. at his Eastham home on 13 October. Sam was a veteran of the Korean War, serving as part of Operation Teapot, the US Army's atmospheric nuclear test program. He received his BS degree from MIT, his Master's in Mathematics from the University of Chicago, and his PhD in Mathematics from Harvard. Before joining the Department in 1967, he worked as an industrial mathematician with Technical Operations and taught for six years at Boston College. While at UMassAmherst, Sam received the Distinguished Teaching Award and authored numerous scholarly journal articles and the groundbreaking book, *Applied Analysis by the Hilbert Space Method. * This reflected his passion for improving mathematics education: the book aimed to convey traditionally advanced mathematics concepts to undergraduate students. After Sam's retirement in 1997, this same passion led him to author an extensive NSF proposal on how to attract more PhD mathematicians into public high school teaching.

### September 2018

At the 60th birthday conference for Bob Gompf at UT Austin (12-15 July 2018) UMass Amherst was represented across the board by Associate Professor R. Inanc Baykur, Visiting Assistant Professors Noriyuki Hamada and Jonathan Simone, PhD candidates Rich Buckman and Andrew Havens, and recent Commonwealth Honors College graduate Kai Nakamura (now a PhD candidate at UT Austin). While there, Inanc gave an invited talk on "Small symplectic and exotic 4-manifolds via positive factorizations."

**UMass Amherst geometric topologists take Texas:** Nakamura, Simone, Gompf, Baykur, Havens, Hamada, Buckman

In June, Professor Tom Braden gave a short lecture course titled "Introduction to category $\mathcal{O}$ and symplectic duality in the hypertoric setting" at Notre Dame, as part of a summer school on geometric representation theory and symplectic varieties for graduate students and postdocs. And during August, Tom flew to Rio de Janeiro, Brazil, where he heard Associate Professor Paul Hacking deliver an invited lecture at the International Congress of Mathematicians on joint work with UT Austin's Sean Keel.

Stathis Charalampidis talked about "Formation of rogue waves in continuous and discrete models: Theory and computation" this summer at the SIAM * Conference on nonlinear waves and coherent structures.* (He is also our new Chief Undergraduate Advisor - kudos, Stathis!)

Visiting Assistant Professor Liubomir Chiriac received a 2018 AMS-Simons travel grant. Administered by the American Mathematical Society with the support from the Simons Foundation, each grant provides an early-career mathematician with funding for two years to be used for research-related travel. Each year UMass Amherst will receive an additional amount equal to 20% of the travel grant to enhance the research environment in our Department.

On 16 June 16 2018, Associate Professor Erin Conlon gave an invited talk "Parallel Markov Chain Monte Carlo Methods for Bayesian Analysis of Big Data" at the International Chinese Statistical Association Applied Statistics Symposium in New Brunswick, New Jersey.

In June, Professor Rob Kusner participated in the conference *Topology in Dimensions 3, 3.5 & 4* at U.C. Berkeley, celebrating the 60th, 70th & 80th birthdays of Abby Thompson, Marty Scharlemann & Rob Kirby, respectively. And in July, he lectured on "Chirality for Crooked Curves" at the *Topology and its Applications* conference at WKU in Bowling Green, Kentucky. Rob also contributed (with Hugh Bray, Fernando Coda Marques, Michael Eichmair, Ailana Fraser, Lan Hsuan Huang, Chika Mese, Bill Minicozzi, Karen Uhlenbeck & S.T. Yau) to the writing (and editing) of "The Mathematics of Richard Schoen" which honors Rick on his recent award of the Wolf Prize. (This tribute is slated to appear in the December *Notices of the American Mathematical Society.*)

Assistant Professor Yao Li reports that he was awarded a Simons collaboration grant for mathematicians, which he will sacrifice because he just received a larger NSF grant (DMS-1813246) for his project "From deterministic dynamics to thermodynamic laws.” He had his paper "On the polynomial convergence rate to nonequilibrium steady state"

accepted by *The Annals of Applied Probability*, and two more of his papers were recently published: “How well do reduced models capture the dynamics in models of interacting neurons?” (joint with Logan Chariker and Lai-sang Young, in *Journal of Mathematical Biology*), and “From billiards to thermodynamic laws: Stochastic energy exchange model” (joint with Lingchen Bu, in *Chaos: An interdisciplinary journal of nonlinear science* - this paper was designated an "editor’s pick).

Assistant Professor Alejandro Morales appeared in the 2018 edition of Latinisms featured in the September *Notices of the AMS* celebrating Hispanic Heritage Month (September 15–October 15). Lathisms is also a website founded in 2016 by Alexander Diaz-Lopez, Pamela E. Harris, Alicia Prieto Langarica, and Gabriel Sosa to provide an accessible platform that highlights the research and mentoring contributions of Latinx and Hispanic mathematical scientists.

Professor Franz Pedit reports: In April and May 2018 he gave a long lecture course on his present research interests titled "Flows of Curves and Surfaces" for PhD students and postdocs at the Yau Mathematical Science Institute at Tsinghua University in Beijing. While in China, he also delivered colloquium talks titled "Gradient flows of Geometric Variational Problems: the Elastic Curve Flow" at both Beijing University and Tongji University, Shanghai. During 1-7 July 2018, he and Mike Wolf (from Rice University) organized the 5 day BANFF-BIRS workshop *Higgs Bundles and Harmonic Maps * at the Casa Matematica Oaxaca (CMO), Mexico. During the last 2 weeks of August, while visiting the SFBTR 106 *Discretization in Geometry and Dynamics* at TU Berlin, Franz wrote the invited contribution "Commutative Hamiltonian Flows on Curves in Real Space Forms" for the special volume celebrating the birthday of Boston University's professor Emma Previato.

And on a more somber note, we mourn the passing on 2 July 2018 of our dear colleague, Professor Richard S. Ellis, an internationally regarded probabilist, and a good friend to many of us on campus and in the community. It's an immeasurable loss to our Department. For many years Richard edited these monthly News Briefs, along with the annual Newsletter, and I – your current editor – enjoyed working with him on both for much of the past decade. As I re-drafted the letter soliciting your briefs this month, I realized it was based on Richard's traditional text, passed down from him to me several years ago. Both the Newsletter and these News Briefs have become Department traditions, shaped by each of us who has taken on the role of editor, but Richard's influence looms large. He and I shared many common interests outside mathematics, particularly an intellectual curiosity about languages and literature, and both of us have been deeply committed to carry on the tradition of publishing. Richard's dedication to this enterprise is evinced by his last email to me: "How's the Newsletter coming along? Just curious...." It was sent on the evening of 1 July 2018.