Physics Colloquium

Winter & Spring – 2025

Location: Willamette Hall, Room 100

If you would like to receive email announcements of upcoming Colloquia, please email hbeach@uoregon.edu to be added to the list.

January 23: Emily Hager – Boston University

Title: Cellular collective behavior in spatially complex environments

Abstract: Collective behaviors are processes in which large-scale patterns arise from fundamentally local interactions among individuals; in biological systems, these can be organisms, cells, or molecules. A critical open question is how collective behaviors are shaped over both mechanistic and evolutionary time scales by the features of the complex natural environments where they occur. Here I use cellular slime mold aggregation, a classic cellular model for collective behavior, to test how cells behave as a group in spatially complex environments. I developed a novel experimental system that allows us to observe slime mold aggregation in geometrically complex 3D environments using microscopy. In this environment, cell groups show novel behaviors, highlighting how the environment affects both the process and the outcome of collective behavior. Strains differ in their ability to aggregate in the 3D system despite aggregating equally well on agar, indicating that certain cell properties are more critical for aggregation in complex environments. In my experiments, strains that make larger structures in 2D also tend to aggregate better in 3D. Together, my work highlights cellular slime molds as a powerful model to identify generalizable principles for the role of the environment in cellular behavior.

January 30: Nathan Belliveau – University of Washington

Title: Electrifying Secrets of Directed Cell Migration

Abstract: Migratory cells integrate chemical and physical cues to move effectively through their environment. In tissue wounds, disruption of the transepithelial potential generates a wound current and associated electric field oriented toward the wound. Numerous skin and immune cell types migrate in response to these electrical cues (a phenomenon known as galvanotaxis or electrotaxis), which plays a critical role in wound healing. Despite its importance, the molecular basis of galvanotaxis and the specific sensor(s) that enable cells to detect and respond to changes in their electrochemical environment have remained elusive.

To uncover the molecular players involved in galvanotaxis, we developed several genome-scale gene knockdown screens in human neutrophils to enable an unbiased investigation of cell motility. Among the genes identified, TMEM154—referred to here as Galvanin—emerged as a putative electric field sensor expressed on the plasma membrane of cells. Inactivation of Galvanin disrupts cell directionality in an electric field, a defect that can be genetically rescued. Strikingly, Galvanin rapidly relocalizes on the cell surface upon electric field exposure, which depends directly on Galvanin’s charge properties and the electric field strength. This protein relocalization is essential for cells to repolarize, correlating with the dynamic changes in membrane protrusion and retraction that are required for motility.

In summary, we identify Galvanin as a novel biosensor critical for galvanotaxis, providing new insights into the mechanisms that support directed cell migration.

February 6: Kelsey Hallinen – Princeton University

Title: Distinct nanocolony morphologies drive bacterial responses in complex environments

Abstract:Individual bacterial cells adopt a wide range of shapes whose physiological functions have been extensively studied. Bacterial nanocolonies also adopt characteristic shapes like clusters and chains that vary significantly even between species with similar single-cell shapes. Despite their ubiquity, the functions of bacterial nanocolony morphologies remain largely unknown. Here I provide evidence that nanocolony morphology is a major determinant of bacterial colonization in flow.

Clinical reports of heart infections present a surprising paradox: bacteria like S. aureus and E. faecalis preferentially colonize areas of high fluid flow. Combining microfluidic devices and computational models, I explored the dynamics of how these two pathogenic species respond to flow. I discovered distinct mechanisms used by the two species to colonize in high fluid flow, and both act at the nanocolony scale. S. aureus grows in a clustered morphology and advection of signaling molecules away from the clustered cells disrupts dispersal signaling. Conversely, E. faecalis grows in a linear chained morphology and mechanical shear forces from flow push cells towards the surface, leading to more cells attached in higher fluid flow. Overall, my work elucidates two distinct mechanisms by which bacterial nanocolony morphologies drive colonization behaviors and introduces a new perspective to consider when exploring bacterial behaviors in complex environments. Looking forward, my research aims to explore nanocolony morphologies, their physical effects, and genetic responses using both experimental and computational methods. This work will expand beyond flow environments to consider cases like antibiotic responses, phage invasion, and multi-species communities.

February 13: Rahul Chajwa – Stanford University

Title: Suspensions with Internal Degrees of Freedom: From the Lab to the Ocean

Abstract: The dynamics of particles in viscous fluids are ubiquitous in both nature and industry. When driven externally (via applied forces) or internally (via intrinsic activity), these particles exhibit intriguing, far-from-equilibrium collective behaviors. In this seminar, I will explore two topics in driven suspensions: (1) the Stokesian sedimentation of shaped particles in laboratory settings [1, 2], where particle geometry gives rise to an effective Hamiltonian, overturning the classic instability of spheres [3]; and (2) the fluid-structure interactions of marine snow observed during ocean expeditions, which reveal hidden viscoelastic degrees of freedom arising from biological mucus [4], suggesting significant modifications to oceanic carbon flux and storage estimates [5]. By contrasting these complementary scientific approaches — one conducted in the controlled environment of the laboratory and the other in the dynamic and complex field setting of the ocean, I will present my research vision, highlighting the immense potential of conducting soft matter physics at sea. My work aims to deepen our understanding of suspension dynamics within the ocean’s biological pump and to inform the development of ocean-based carbon removal technologies. In doing so, I seek to cultivate a research practice that bridges disciplines and settings.

February 20: Hungtang Ko – Princeton University

Title: Macroscopic active matter: from insect collectives to robot swarms

Abstract: Biological collectives across scales display remarkable emergent behaviors, forming wholes greater than the sum of their parts. While extensive research has been conducted on how microscopic organisms self-organize to achieve biological functions, our understanding of how macroscopic organisms, from insect swarms to fish schools, facilitate their collective behaviors in complex physical environments remains limited. In this talk, I will demonstrate how red imported fire ants and black soldier fly larvae leverage mechanical interactions in their self-organization and how fish-like robots may be used to reveal unique insights about the hydrodynamic interactions within fish schools. Furthermore, I will discuss the exciting opportunities in researching macroscopic active matter, highlighting potential collaborations across diverse research communities from marine biologists to swarm roboticists. This research not only pushes the frontier of biological physics but also paves the way for constructing a unifying theory of active systems across scales.

Fall 2024	Winter 2025	Spring 2025
October 3 – Richard TaylorTitle: State of the Department	Title:	Title:
October 10 – Dietrich BelitzTitle: Long-Range Correlations and Fluctuation-Dissipation Relations in Non-Equilibrium Fluids	Title:	Title:
October 17 – David AllcockTitle: Oregon Ions – A brief history	Title:	Title:
October 24 – Mark RaizenTitle: Isotopes in Medicine, and Meeting Rutherford’s Challenge	Title:	Title:
October 31 – Dhiman RayTitle: Deep Learning Augmented Simulation of Biomolecules	Title:	Title:
November 7 – Leenoy MeshulamTitle: Bridging scales in biological systems – from octopus skin to mouse brain	Title:	Title:
November 14 – Akshay MurthyTitle: Understanding and Eliminating Sources of Loss in Superconducting Qubits	Title:	Title:
November 21 – Julien GuyTitle: The Dark Energy Spectroscopic Instrument First Year Results: Cosmic Expansion History with Baryon Acoustic Oscillations	Title:	Title:
December 5 – Matt GrahamTitle: Driving Electronics with Micro-Defects and Femto-Spin Flips	Title:	Title:

Fall 2023	Winter 2024	Spring 2024
September 28 – Richard Taylor Title: State of the Department	January 18 – Reina MaruyamaTitle:	April 4 – David WinelandTitle: Atomic Clocks and Einstein’s relativity
October 5 – John TonerTitle: Birth, Death, and Flocking: The Hydrodynamics of Dry Active matter	January 25 – Mustafa AminTitle:	April 11 – Matthew JemielitaTitle: Antibody Design and Optimization with Generative Unconstrained Intelligent Drug Engineering
October 12 – Spencer ChangTitle: General New Physics Observables at Colliders	February 1 – Leenoy MeshulamTitle:	April 18 – Francis HalzenTitle: IceCube: The First Decade of Neutrino Astronomy
October 19 – Rob PhillipsTitle:	February 8 – Flip TanedoTitle: Why we have not discovered dark matter: a theorist’s apology	April 25 – Miranda Holmes – CerfonTitle: Modeling particles programmed by DNA
October 26 – Carol PattyTitle: Exploring the Magnetosphere of an Ice Giant: Probing Uranus is No Laughing Matter	February 14 – Tracy SlatyerTitle: Dark Matter, Cosmic Background Radiation, and the Birth of the First Stars	May 2 – Kyle WelchTitle: Physical Review Letters: A Peek Behind the Cover
November 2 – Leif KarlstromTitle: The intrinsic and extrinsic geometry of Earth surface topography	February 22 – Herman BatelaanTitle:	May 9 – Varda HaghTitle: Finding order in disorder through permutation symmetry
November 9 – Marianna SafranovaTitle:	February 29 – Christopher MonroeTitle: Quantum Computing Systems with Individual Atoms	May 16 – Fahad MahmoodTitle: Revealing emergent phenomena in correlated topological materials using femtosecond light
November 16 – Sid NagelTitle: Disorder is different	March 7 – Tova HolmesTitle:	May 23 – Jessica HoehnTitle: Embedding diversity, equity, and inclusion in our physics classes
November 30 – Mark RaizenTitle: Isotopes, Maxwell’s demon, and The Pointsman Foundation	March 14 – Tien-Tien YuTitle: Exploring the Quantum Universe: Pathways to Innovation and Discovery in Particle Physics	May 30 – Zeb RocklinTitle: Fundamental Physics of Flexible Structures
		June 6 – Johannes PollanenTitle: Hybrid quantum phononics with superconducting qubits

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