# Faculty News Briefs

### 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.

Professor Rob Kusner was re-elected to the Board of Trustees of AMIAS – the Association of Members of the Institute for Advanced Study – and participated in the workshop there the following week (5-9 November) on Mean Curvature in Geometric Analysis. 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 eve of 1 July 2018.

### May 2018

Calden named Instructional Innovation Fellow

Four faculty from the College of Natural Sciences, including our own Senior Lecturer Adena Calden, were recently selected through a highly competitive process to participate in the Summer 2018 Innovate@ Symposium that runs 21-24 May 2018. These symposia, led as a collaboration between TEFD, UMass Libraries, and IT, provide a unique opportunity to have hands-on instruction, to work with colleagues, and then try out the tools. Symposia members will also become part of an innovation think tank as Innovation Fellows that will be brought together to consider new instructional innovations throughout the academic year.

Over a hundred UMass faculty have participated in the Innovate@ Symposium. Including the four most recent additions, there are now 29 Innovation Fellows in the College of Natural Sciences. Each Innovate Fellow has an innovation page where they discuss their proposed instructional innovations, upload videos of presentations to the Symposium participants, or highlight recent accomplishments.

Austin Rohlfing, Math Undergrad, wins Grinspoon Award

Austin Rohlfing was presented with a Grinspoon Entrepreneurial Spirit Award on 25 April. Austin’s startup, TernBooking, has combined travel accommodations with savings and budgeting for a trip. TernBooking has competed in four rounds of Berthiaume Center’s Innovation Challenge and currently maintains work space in the Berthiaume incubator. The venture will also participate in Berthiaume’s 2018 Summer Accelerator program.

Kudos to our three SCUDEM teams

On Saturday 21 April, three teams from UMass Amherst presented their work for the Spring 2018 Student Competition Using Differential Equations Modeling (SCUDEM). Starting on 13 April, each team of three students worked together on their choice of one of three modeling scenarios. On the day of the competition, they were given an additional twist to their problem to address, before presenting their model in a 2-page executive summary as well as a 10-minute presentation.

The first team, consisting of Enya Truong, Henry Phan, and Sharath Ramkumar worked on "Modeling the Cool Kids," using graph theory and Markov Chains to explain how clusters of social interactions form and break. The second team, consisting of Fusheng Yang, Joe Shao, and Hui Kennedy worked on "Sorting Recyclables," where they modeled the separation of paper and cardboard materials with a fan. Their model included the differences in acceleration and drag on the two materials, and they were awarded "meritorious" mention. The third team, consisting of Jonah Chaban, Jimmy Hwang, and Artem Vysogorets also worked on "Sorting Recyclables." They included detailed modeling of tumbling paper along with random orientation of the paper stream, and they were awarded an "outstanding" mention (they also finished first in the Fall 2017 competition).

Assistant Professor Matthew Dobson served as the faculty coach for our three teams, and also led the morning development session for the other faculty coaches.

And in other news....

Professors Tom Braden and Rob Kusner, Visiting Assistant Professor Jacob Matherne (who's heading to the Institute for Advanced Study in Princeton next year - kudos to Jacob), and PhD candidate Andrew Havens were among attendees at the Spring AMS sectional meeting at Northeastern University. On 21 April, Tom gave a talk in the Arrangements of Hypersurfaces special session on "Equivariant cohomology and intersection cohomology of a completion of a hyperplane arrangement," while Rob spoke on "Geometry and stability of critical point-configurations in $S^2$ and critical links in $S^3$" at the Discretization in Geometry and Dynamics special session 22 April.

Vlad Emelyanov, a graduating senior in CS with a Mathematics minor, developed online assessment materials for statistics courses at UMass this semester under the supervision of VAP Eric Hall. These resources were also contributed to the Open Problem Library of WeBWorK, a nationally used open-source online homework system supported by the MAA and NSF. This curriculum development project was undertaken with a Flex Grant from the Institute for Teaching Excellence and Faculty Development at the University of Massachusetts Amherst.

Distinguished Professor Panos Kevrekidis has published his third paper in Nature Communications this academic year . In addition to To infinity and some glimpses of beyond and Direct measurement of superdiffusive energy transport in disordered granular chains, his paper Interactions and scattering of quantum vortices in a polariton fluid has just appeared. Panos's new book, co-authored with VAP Christopher Chong, on Coherent Structures in Granular Crystals: From Experiment and Modelling to Computation and Mathematical Analysis has also been published recently by Springer-Verlag.

During 2-3 April, Professor Michael Lavine served on a committee reviewing the Department of Computer Science & Statistics at the University of Rhode Island. He also delivered a talk at the New England Statistics Symposium, held at UMass on 14 April. Patrick Flaherty and Anna Liu were among the organizers of the Symposium.

Professor Ivan Mirkovic reports that "one of our faculty has been elected as a corresponding member of the Academy of Sciences in the picturesque Balkan country of Croatia" - here "corresponding" means the member lives outside the country - kudos to Ivan!

At Northeastern University on 5 April, and at Yale University on 26 April, Marshall H. Stone VAP Luca Schaffler gave seminar talks titled "Equations for point configurations to lie on a rational normal curve."

News Briefs will return in the Fall. Have a pleasant summer!

### April 2018

Visiting Assistant Professor Stathis Charalampidis gave a talk titled "Formation of rogue waves in continuum and discrete models: Theory and Computation" during the AMS Sectional Meeting at Ohio State University on Saturday 17 March.

Professor Michael Lavine attended the OSAC all-hands meeting in Chicago between 20 and 23 March as a member of the fingerprint subcommittee; OSAC is an arm of NIST. He became an Associate Editor for a special issue of The American Statistician on statistical inference in the 21st century, and had a paper "Frequentist, Bayes, or Other?" accepted for publication there.

In a research seminar at MSRI on 7 March, Associate Professor Alexei Oblomkov presented his joint work with Andrei Okounkov and Rahul Pandharipande. He is a Research Professor at MSRI for the Spring semester as a part of its Enumerative Geometry Beyond Numbers program. Alexei was also named a Simons Fellow for the year 2018. (The Simons Foundation supports a one-semester extension of his sabbatical leave, and Alexei plans to visit his collaborators during the Fall semester.)

Professor Franz Pedit gave colloquium talks, at the University of Innsbruck on 9 March and at the Technical University Vienna on 15 March, titled "Gradient flows of geometric variational problems: the elastic curve flow." He also gave a plenary lecture of the same title at the workshop Geometry of Submanifolds and Integrable Systems organized by the International Research Network Project “Symmetry, Topology and Moduli” at the Osaka City Advanced Mathematical Institute during 23-30 March. After that, Franz embarked for Beijing to spend 3 months in the Yau International Mathematical Institute at Tsinghua University.

On 9 March, Professor HongKun Zhang gave both a colloquium talk on "Various diffusion behavior of Lorentz gases" and a Dynamical Seminar talk on "Markov partitions for hyperbolic systems with singularities" at the Mathematics Department of Indiana University–Purdue University, Indianapolis. Between 18-23 March, HongKun attended the conference New Developments in Open Dynamical Systems and Their Applications at Banff, Canada, of which she was one of the main organizers. The conference, supported by the Banff International Research Station for Mathematical Innovation and Discovery (BIRS), brought together more than 40 participants from around the world, including many leading experts in the field of dynamics related to open systems. Diverse branches of research in this field have applications ranging from quantifying the occurrence of rare events, such as large storms or financial crises, to understanding the fundamentals of thermodynamics. By studying connections between these various types of open systems, the conference promoted progress and fostered new directions of research in this rapidly developing area of dynamics.

!!! Newsflash !!!

Kudos to our three SCUDEM teams!!!

On Saturday 21 April, three teams from UMass Amherst presented their work for the Spring 2018 Student Competition Using Differential Equations Modeling (SCUDEM). Starting on 13 April, each team of three students worked together on their choice of one of three modeling scenarios. On the day of the competition, they were given an additional twist to their problem to address, before presenting their model in a 2-page executive summary as well as a 10-minute presentation.

The first team, consisting of Enya Truong, Henry Phan, and Sharath Ramkumar worked on "Modeling the Cool Kids," using graph theory and Markov Chains to explain how clusters of social interactions form and break. The second team, consisting of Fusheng Yang, Joe Shao, and Hui Kennedy worked on "Sorting Recyclables," where they modeled the separation of paper and cardboard materials with a fan. Their model included the differences in acceleration and drag on the two materials, and they were awarded "meritorious" mention. The third team, consisting of Jonah Chaban, Jimmy Hwang, and Artem Vysogorets also worked on "Sorting Recyclables." They included detailed modeling of tumbling paper along with random orientation of the paper stream, and they were awarded an "outstanding" mention (they also finished first in the Fall 2017 competition).

Assistant Professor Matthew Dobson served as the faculty coach for our three teams, and also led the morning development session for the other faculty coaches.

### March 2018

On 21 February, Visiting Assistant Professor Jeremiah Birrell spoke in the Mathematical Physics and Probability Seminar at the University of Arizona; his talk was titled "Small Mass Limit of Noisy Inertial Particle Dynamics: Homogenization, Instantaneous Equilibration, and Entropy Production."

The 2017 William Lowell Putnam exam results are in: out of 575 participating institutions in the US and Canada, UMass Amherst ranked 46th, an excellent result! (Last year we ranked 55th out of 568.) Our three team members were Alexander Fischer, James Hagborg and Artem Vysogorets. James did particularly well, placing in the top 7% of the 4638 students taking the Putnam last December; Patrick Lei also had a noteworthy individual performance. Many thanks to VAP Liubomir Chiriac for his fine job running the Putnam seminar last fall.

Assistant Professor Nestor Guillen is applying his professional expertise to the topic of Gerrymandering. On 4 February he spoke at the Austin Gerrymandering Workshop, with a presentation about optimal transport and calculus of variations perspectives on redistricting. Nestor was also a part of the “Gerrymandering Steals Elections: Learn How It’s Done and How to Stop It" panel in Northampton on 12 February; moderated by former mayor Clare Higgins, other panelists were U. S. Representative Jim McGovern, State Representative Paul Mark, and Adam Hilton of Mount Holyoke College.

Assistant Professor Alejandro Morales gave the colloquium at the Tulane University math department on 29 February (OK, 1 March). His topic was "Volume and lattice point formulas for flow polytopes."