Distinguished Seminar in Computational Science and EngineeringApril 17, 2025, 12-1PM45-432 in Building 45 and Zoom WebinarSlender and close: accurate Stokes flows for rigid particles in challenging geometriesAlex Barnett Group Leader, Numerical Analysis. Center for Computational Mathematics, Flatiron Institute, NYAbstract:The modeling of suspensions of rigid particles in a viscous incompressible fluid in the low-Reynolds-number limit is crucial to applications including sedimentation, rheology, microfluidic devices, active matter, and bacterial or cellular transport. Accurately modeling the relation between hydrodynamic forces and motions demands solving a Stokes boundary-value problem throughout the fluid domain at every time-step, yet the available numerical tools are far from satisfactory. This is especially true when objects become relatively close (“lubrication effects”). I will overview two new tools to address this with controlled accuracy using potential theory: 1) For the common case of spheres we show that interior fundamental solutions (MFS) augmented by simple image systems accurately handle separations down to a thousandth of the radius, and that large collections of spheres/ellipsoids can be tackled via block-diagonal least-squares preconditioning. 2) For slender fibers of circular cross-section we present a boundary integral (BIE) scheme with adaptive quadrature. Unlike widely-used slender body theory—which is non-convergent (merely asymptotic in the fiber radius) and incorrect when fibers approach—our scheme is convergent, and handles very close fibers with up to 10 accurate digits. We combine it with high-order time-stepping for sedimentation. For both tools we show high-order convergence, and well-conditioned iterative solution with close-to-linear cost scaling.Joint work with Anna Broms, Anna-Karin Tornberg, and Dhairya Malhotra.Bio:Alex Barnett is an applied mathematician and numerical analyst. He is a Senior Research Scientist, and Group Leader for Numerical Analysis, at the Center for Computational Mathematics at the Flatiron Institute in New York City. After a Ph.D in physics from Harvard, he did postdoctoral work in radiology at Massachusetts General Hospital and as a Courant Instructor at New York University. He served on the mathematics faculty at Dartmouth College for 12 years, becoming a full professor, and creating several new courses on topics such as the math of music and sound. His research includes numerical partial differential equations (wave scattering, Stokes flow, and high-frequency eigenvalues), integral equations, fast algorithms, signal processing, statistics, imaging, inverse problems, quantum physics and biomathematics. He has authored or coauthored over 70 articles and two books, and developed popular scientific software libraries. His awards include several NSF grants, Dartmouth's Karen E. Wetterhahn Memorial Award for Distinguished Creative or Scholarly Achievement, and 1st prize in the 1990 International Physics Olympiad.

About the presentation: Most people are aware of the US fentanyl problem, but not necessarily of its magnitude. The number of deaths reported by the CDC began increasing sharply in 2013 from about 3,000 annual deaths to over 75,000 deaths in 2022. This rapid increase in only about 10 years was unexpected, and death rates continue to rise. A simple supply-and-demand relationship gives a rationale. A deeper dive into CDC data reveals that age groups most impacted are those in their 20s and 30s, which includes college undergraduates. On the supply side, US Border Patrol seizures increase annually. In 2023, over 27,000 pounds of illicit fentanyl were seized, which is enough to kill every person in the US over 18 times. Multiple factors have caused the increase of illicit fentanyl over time -- border porosity, more aggressive Mexican cartel smuggling operations, and increased shipments of fentanyl precursors to those cartels. Possible solutions will be presented.Dr. Donna Nelson obtained her PhD in chemistry at UT-Austin with Michael Dewar and did her postdoctorate at Purdue with HC Brown. She was the first female and only Native American to accept a professorship at the University of Oklahoma Department of Chemistry. She has published over 200 papers, given thousands of talks, and organized hundreds of ACS symposia. She has received many honors, including the Guggenheim Award, ACS Fellow, AAAS Fellow, and NSF Creativity Extension.Dr. Nelson was science advisor for the hit television show "Breaking Bad" and was elected to 2016 President of the American Chemical Society. Her research and creative activities focused on the topics listed above as talk subjects by building communities in them.This event is hybrid. Please choose your ticket accordingly.We are committed to making this event fully accessible to everyone who wants to attend. Please let us know if there is anything you need to participate fully in this event by e-mailing vulfp@mit.edu.Photographs and/or videos may be taken at this event.By entering and attending this event, you acknowledge and agree that your likeness and/or voice may be included in photos and videos of the event and used by MIT in connection with communications about the Institute Community and Equity Office or in other MIT communications.If you do not agree to this usage, please notify the event organizer or do not enter the event.

Have some fun(nel) on a tunnel or sun(nel) walk! Join us for a 30-minute volunteer-led walk either through MIT's famous tunnel system or around Killian Court. As the weather gets warmer, walk leaders may choose to take the group outside. Is the weather warm and you missed the start? Find the group on Killian Court and join in!Location details: Meet in the lobby under the “Belonging + Community” banner. Location photo below.Sun(nel) Walk Leaders will identify themselves by holding a white at the meeting location.Prize Drawing: Attend a walk and scan a QR code from the walk leaders to be entered into a drawing for a getfit canvas boat tote bag at the end of the getfit challenge. The more walks you attend, the more entries you get. Winner will be drawn and notified at the end of April. Winner does not need to be a getfit participant.Disclaimer: Tunnel walks are led by volunteers. In the rare occasion when a volunteer isn’t able to make it, we will do our best to notify participants. In the event we are unable to notify participants and a walk leader does not show up, we encourage you to walk as much as you feel comfortable doing so. We recommend you check this calendar just before you head out!Getfit is a 12-week fitness challenge for the entire MIT community. These tunnel walks are open to the entire MIT community and you do not need to be a current getfit participant to join.

MIT Free English Class is for international students, sholars, spouses. Twenty seven years ago we created a community to welcome the nations to MIT and assist with language and friendship. Join our Tuesday/Thursday conversation classes around tables inside W11-190.

Have some fun(nel) on a tunnel or sun(nel) walk! Join us for a 30-minute volunteer-led walk either through MIT’s famous tunnel system or around Killian Court. As the weather gets warmer, walk leaders may choose to take the group outside. Is the weather warm and you missed the start? Find the group on Killian Court and join in!Location details: Meet in the lobby with the big mirror, right inside the Collier Memorial entrance to Stata. Location photo below.Sun(nel) Walk Leaders will identify themselves by holding a white flag at the meeting location.Prize Drawing: Attend a walk and scan a QR code from the walk leaders to be entered into a drawing for a getfit canvas boat tote bag at the end of the getfit challenge. The more walks you attend, the more entries you get. Winner will be drawn and notified at the end of April. Winner does not need to be a getfit participant.Disclaimer: These walks are led by volunteers. In the rare occasion when a volunteer isn’t able to make it, we will do our best to notify participants. In the event we are unable to notify participants and a walk leader does not show up, we encourage you to walk as much as you feel comfortable doing so. We recommend checking this calendar just before you head out!Getfit is a 12-week fitness challenge for the entire MIT community. These walks are open to the entire MIT community and you do not need to be a current getfit participant to join.

"Science Engagement for a Better Society" is a dynamic event exploring how researchers and the public can collaborate to harness science for social good. Through interactive discussion with a panel of experts we will examine strategies to improve public trust in science, communicate complex findings effectively, and ensure that innovation serves diverse communities. Featuring leading scientists, communicators, and advocates, this event will highlight the role of engagement, transparency, and inclusion in shaping ethical and impactful scientific progress.Speakers include: Seth Mnookin, Associate Professor, Comparative Media Studies/Writing Deb Roy, Professor of Media Arts and Sciences, Director of the MIT Center for Constructive CommunicationModerated by: Marzyeh Ghassemi, Associate Professor, Electrical Engineering and Computer ScienceCo-organized by: Amy Brand, Director, MIT Press Marzyeh Ghassemi, Associate Professor, Electrical Engineering and Computer Science Crystal Lee, Assistant Professor, Schwarzman College of Computing & Comparative Media Studies/WritingThis event is co-sponsored by the MIT chapter of the American Association of University Professors (AAUP), MIT Press, and the MIT Libraries.