Speaker: Vincent Tournat (CNRS, Le Mans Université / Harvard)Title: Dynamics of multistable mechanical metamaterials: recent results on nonlinear waves, transition fronts and their interactionsAbstract:The class of flexible mechanical metamaterials, which encompasses architected materials composed of highly compliant parts connecting much stiffer and heavier parts, has recently been systematically explored thanks to emerging techniques for their realization and accurate lumped-parameter models describing their dynamics. Examples of such metamaterials include kirigami, origami, elastic lattices with various topologies composed of rotating mass units connected by thin, flexible hinges, or systems of coupled buckled beams… These metamaterials can undergo large deformations and are known to support a wide variety of nonlinear waves, such as vector solitons, breathers, cnoidal waves, among others. Interestingly, by designing these materials with multistable inclusions, such as elastically coupled bistable mechanical units, we can observe phenomena such as transition waves. The transition wave presents itself as a progressive front travelling through the material as the multistable units sequentially switch from one equilibrium state to another, eventually leading to a partial or full reconfiguration of the structure.In this talk, I will highlight the fundamentals and a selection of recent results on nonlinear waves in flexible mechanical metamaterials and in particular transition waves in multistable metamaterials. Through theoretical, numerical and experimental examples, I will discuss some salient properties of these nonlinear waves and their interactions. While in the case of zero damping we find the wave dynamics generally obey the nonlinear KleinGordon equations, the presence of a significant nonzero damping heavily influences the multistable response and permits transition fronts that result from nonlinear reactiondiffusion equations. This class of flexible metamaterials thus gives rise to the emergence of specific properties not necessarily found in other waves supported by discrete and/or nonlinear media, and which can be rationally harnessed, e.g., strong non-reciprocity, robustness of the wave profile, extreme amplitude-dependent behavior… These metamaterials and their dynamics can therefore be designed and implemented for applications involving the local or global reconfiguration of a medium, the manipulation of a mechanical memory, the control of waves in space and time, mechanical computing and more generally to be the vector for embedded material intelligence.

Ten minutes for your mind@2:50 every day at 2:50 pm in multiple time zones:Europa@2:50, EET, Athens, Helsinki (UTC+2) (7:50 am EST) https://us02web.zoom.us/j/88298032734Atlantica@2:50, EST, New York, Toronto (UTC-4) https://us02web.zoom.us/j/85349851047Pacifica@2:50, PST, Los Angeles, Vancouver (UTC=7) (5:50 pm EST) https://us02web.zoom.us/j/85743543699Almost everything works better again if you unplug it for a bit, including your mind. Stop by and unplug. Get the benefits of mindfulness without the fuss.@2:50 meets at the same time every single day for ten minutes of quiet together.No pre-requisite, no registration needed.Visit the website to view all @2:50 time zones each day.at250.org or at250.mit.edu

Speaker: Vasudevan Srinivas (Tata and Univ. of Buffalo)Title: Some finiteness results for the etale fundamental group in positive characteristicsAbstract:This talk will discuss some results on etale fundamental groups of varieties over an algebraically closed field of characteristic p > 0, based on joint work with Hélène Esnault and other coauthors. One result, along with Mark Shusterman, is that the tame fundamental group is finitely presented for such a variety which is the complement of an SNC divisor in a smooth projective variety. A second, along with Jakob Stix, is to give an obstruction for a smooth projective variety to admit a lifting to characteristic 0, in terms of the structure of its etale fundamental group as a profinite group. We will finally touch on some open questions.

Time: 12:00 PMLocation: New London, CT

“Thinking vs. Doing: Cognitive Capacity, Decision Making and Medical Diagnosis” | Jonathan Kolstad (Haas School of Business, University of California Berkeley)

Speaker: David Eisenberg, UCLAHost: Amy KeatingTitle: "Surprising mechanism of small molecules that disassemble pathological amyloid fibrils associated with neurodegeneration" The Rich LectureThe Biology Colloquium is a weekly seminar held throughout the academic year — featuring distinguished speakers in many areas of the biological sciences from universities and institutions worldwide. More information on speakers, their affiliations, and titles of their talks will be added as available. Unless otherwise stated, the Colloquium will be held live in Stata 32-123 (Kirsch auditorium) Contact Margaret Cabral with questions.