Host: Dr. Surabhi Sachdev

Title: Recent gravitational wave discoveries from LIGO, Virgo and KAGRA

Abstract:

 The LIGO-Virgo-KAGRA collaboration completed its 30-month-long fourth observing run late last year where hundreds of new gravitational wave sources comprised of neutron stars and black holes were identified.  These discoveries included the clearest gravitational wave sources yet which provided unprecedented tests of general relativity, and unexpectedly massive black holes. In this presentation I will present recent results from the fourth observing run and describe plans for the next observing run which starts this fall.

Bio: Chad Hanna is a Professor of Physics and Astronomy & Astrophysics, a co-hire of the Institute for Computational and Data Science (ICDS), and a member of the Institute for Gravitation and the Cosmos (IGC) at Penn State. His research focuses on the detection and characterization of gravitational waves from merging neutron stars an black holes with the LIGO Scientific Collaboration and he leads efforts to detect gravitational waves in real-time to support multi-messenger astrophysics. 

Host: Dr. Matthew Liska

Title: What Are We Learning About Super-Eddington Accretion Disks From Simulations?

Abstract: Accretion of gas onto black holes is one of the most important processes shaping our Universe. Understanding extremely high rates of accretion (dubbed `super-Eddington') is vital to explaining the challenging observation that supermassive black holes (SMBHs) are fully formed at redshifts >7. It is also important to understanding astrophysical objects such as tidal disruption events (TDEs) and ultra-luminous X-ray sources (ULXs). While we are able to perform observations of super-Eddington accreting systems, to understand them more fully, we must turn to numerical studies. In this talk, I will present the results of some recent super-Eddington disk simulations and discuss some of the interesting things we are learning.

Host: Prof. Tamara Bogdanovic

Title: A New Era of Time-Domain Astronomy: Catching the Fastest, Brightest, and Most Interesting Astronomical Events

Abstract:

 Time-domain astronomy–the study of astronomical events that appear, change in brightness, and disappear on timescales of seconds to years–is currently undergoing a revolution. Survey missions such as the Legacy Survey of Space and Time on the Vera Rubin Observatory, which images the night sky repeatedly, are set to detect millions of these objects each night. This deluge of data opens new discovery spaces, allowing us to identify the fastest-evolving, brightest, and rarest events, and to study them in unprecedented detail. In this talk, I will discuss the current state of time-domain astronomy, focusing on two explosive phenomena: supernovae, the explosive deaths of stars, and kilonovae, the optical counterparts to binary neutron star mergers. Both are intricately tied to many areas of physics and astronomy, from enabling cosmological measurements to providing unique views into the origins of heavy elements and exotic states of matter. I will detail what we currently understand about these objects as well as future studies that will lead to greater insights into their underlying physics. Finally, I will discuss the broader time-domain discovery and follow-up ecosystem, including how alerts are generated, disseminated, and rapidly followed across multiple telescopes and wavelengths. I will introduce a new NASA-led initiative, ACROSS, which aims to improve coordination and response to rare or high-impact transient events, such as nearby supernovae or neutron star mergers—phenomena where rapid observations across the electromagnetic spectrum are critical.

Host: Prof. JC Gumbart

Title: Physics-Informed Machine Learning for Protein Dynamics: From RNA Polymerase Inhibition to Targeted Protein Degradation

Abstract:

 Protein dynamics are fundamental to protein function and encode complex biomolecular mechanisms. In this talk, I will explore how incorporating dynamics memory (i.e., non-Markovian effects) into machine learning models can greatly improve both the efficiency and accuracy of predicting long-time dynamics in complex biomolecules. Specifically, I will introduce MEMnets, a deep learning framework for identifying the slow collective variables (CVs) of protein dynamics. Unlike conventional deep learning models such as VAMPnets, which assume Markovian dynamics, MEMnets builds on our own integrative generalized master equation (IGME) theory with a novel loss function that minimizes the time integration of memory kernels. We demonstrate that MEMnets-derived CVs elucidate the molecular mechanism underlying the loading gate opening of bacterial RNA polymerase (RNAP), revealing a transiently open cryptic pocket that binds the antibiotic Myx. In addition, we apply these methods to Targeted Protein Degradation (TPD)—an emerging therapeutic strategy that eliminates, rather than inhibits, disease-causing proteins. TPD agents such as PROTACs and molecular glues work by stabilizing weak or transient protein–protein interactions (PPIs) between the target protein and an E3 ubiquitin ligase, thereby marking the target for proteasomal degradation. These metastable PPIs are central to TPD activity but remain notoriously difficult to predict. Using our approach, we predict metastable PPIs between E3 ligases (VHL) and target proteins (KRAS or RIP1 kinase). Remarkably, one of our predicted complexes closely matches an experimentally determined co-crystal structure. Building on this, we use these metastable PPIs to steer AlphaFold3’s generative process for virtual screening of TPD agents. Finally, I will introduce TS-DART, another deep-learning method that automatically identifies transition states (TS) across multiple free energy barriers in biomolecular systems. Inspired by trustworthy AI, TS-DART detects TS as out-of-distribution data in a hyperspherical latent space, providing a robust and automated way to characterize rare events in biomolecular dynamics.

Host: Dr. Itamar Kolvin

Title: From Chaos to Control: Structure Formation in Active-Passive Mixtures

Abstract:

Active matter is composed of particles that move by consuming energy, creating materials that can flow, deform, and self-organize far from equilibrium. These active fluids are often chaotic, yet that very chaos offers opportunities for structural control. Understanding how activity couples to material organization provides a path toward designing reconfigurable and controllable soft materials. We study mixtures where an active liquid crystal coexists with a passive fluid and show that active stresses destabilize interfaces, producing traveling waves and spontaneous self-folding that have no analogue in equilibrium systems. In bulk mixtures, activity gives rise to connected filamentary networks in two dimensions, while in three dimensions it generates dynamically arrested, labyrinthine bicontinuous structures that continuously reorganize without coarsening. Together, these results reveal how local energy input and compositional demixing can combine to create self-organized, reconfigurable materials, offering new ways to control morphology and flow in active-passive systems.

Host: Prof. John Wise

Title: Coronal Heating and Feedback from Luminous Accretion Flows: Challenges and Insights from Local and Global Simulations

Abstract

Radiatively efficient accretion represents a frontier problem for computational astrophysics. Through leveraging GPU acceleration and exascale supercomputer architectures, the H-AMR Collaboration, led out of Georgia Tech, has been working to understand the structure of accretion flows onto black holes, where strong magnetic fields, two-temperature plasma physics, radiation transport, and general relativity may all imprint themselves on the radiative and kinetic feedback observed from black-hole-powered sources. In this talk, I will discuss our ongoing efforts to model accretion flows across a wide range of accretion rates, from the radiatively inefficient regime powering targets of the Event Horizon Telescope, to the super-Eddington regime, which may be relevant for sources such as tidal disruption events, ultra-luminous X-ray sources, and quasars. Special attention is given to the thin-disk regime at around 1 to a few tens of percent of the Eddington limit, where hard X-ray emission, thought to emerge from a hot (billions of Kelvin) "corona," is routinely observed. I will discuss two different models for the coronal geometry, the "sandwich" and "truncated disk" models, and what we have learned about possible coronal heating mechanisms based both on the local stratified shearing-box calculations I explored during my Ph.D., and the especially high-resolution global simulations that I have been exploring here at Tech.

Host: Dr. Itamar Kolvin

Title: "Don't get stuck: (no)flow and clogging of suspensions"

Abstract:

From pipes to aquifers to medical devices, stopping the flow is always inconvenient and sometimes dangerous. Clogging can occur in confined flows of particulate suspension that carry either too many particles or particles that are too large or sticky. As a result, clogging is problematic in many engineering systems: printer nozzles, drip irrigation lines, autoinjection devices, pipes, ...

The challenge in studying the clogging of fluid systems by suspensions is that the underlying physics is complex and spans many length scales (from colloids to boulders) and time scales (from less than a second to years). In this talk, we will discuss how and why flowing stuff gets stuck. In particular, we will highlight the role of the different clogging mechanisms at play in various systems and our recent efforts to characterize, model, and prevent - or at least delay - the clogging of fluidic systems. We will also consider different potential methods to limit clogging in some applications. Predicting when clogging is likely to occur and working to prevent it can lead to new design principles to develop clog-resilient systems and improve the reliability of fluidic systems dispensing particulate suspensions.

Bio: Alban Sauret is an Associate Professor and Clark Faculty Fellow in the Department of Mechanical Engineering at the University of Maryland, College Park. After a BS, MS, and PhD in Physics obtained in France and a Postdoctoral Research position at Princeton University, he became a CNRS research scientist in France from 2014 to 2018. He then served on the faculty at UC Santa Barbara from 2018 to 2024 before joining Maryland in 2025. His honors include the NSF CAREER Award, the Milton van Dyke Award, and ASME’s Rising Star of Mechanical Engineering. He was selected as a Soft Matter Emerging Investigator and later a Pioneering Investigator, and received the APS Reviewer Excellence Award. He has served as a guest editor for the International Journal of Multiphase Flow. His research lies at the intersection of fluid mechanics, soft matter, interfacial dynamics, and granular physics, aiming to understand the dynamics of multiphase systems for a broad range of applications from manufacturing to water sustainability or geosciences. He received various awards, such as a Soft Matter Emerging Investigator Award in 2017 and Pioneering Investigator Award in 2024 from the Royal Society of Chemistry, an NSF CAREER Award in 2020, an American Physical Society Milton van Dyke award in 2021, an ASME Rising Star of Mechanical Engineering in 2024, and became a Moore Foundation Experimental Physics Investigator in 2025.

Host: Dr. Gongjie Li

Title: Mapping Sub-stellar Companions in Time and Space

Abstract: Companion brown dwarfs and exoplanets are complex objects whose time and spatial variability are now being mapped with high-fidelity infrared observations from JWST. I will begin by presenting our analysis of JWST NIRSpec/IFU PRISM observations of the 2M1207 system that represent the first spectroscopic time monitoring of a planetary-mass companion simultaneously with its host. By monitoring the variability of the system as a whole, we are sensitive both to the time evolution of atmospheric structure --- including through hot spots and clouds --- as well as external variability such as the accretion of disk material. 2M1207 A's spectra show multiple time-dependent structures across the near-infrared. While we do not see a full rotation within our observations, we do capture non-linear trends in time across much of the spectra, with localized regions showing light curves that hint at the possibility of variability imparted by the circum-stellar disk. The planetary-mass 2M1207 b's spectra generally corroborate the interpretation of recent atmospheric characterizations, where a simple cloud evolution model can capture most of the short-term variability. Turning to spatial variability, I will also provide a first look at the eclipse mapping of brown dwarfs in orbit around white dwarfs. These systems provide a unique opportunity to study the spatially-resolved structures of highly-irradiated atmospheres. Finally, I will highlight ongoing student research in brown dwarfs and exoplanets at UVA, which includes the spectral and orbital characterization of the aforementioned brown-dwarf/white-dwarf binaries as a complement to atmospheric studies, as well as classifying the seasonal evolution of Earth's vegetation as spectral signatures of the response of the majority of Earth's life by mass to the solar energy budget.

Host: Prof. Zhigang Jiang

Title: Deterministic quantum trajectory via imaginary time evolution

Abastract: Quantum trajectories—individual realizations of a quantum system’s evolution under unitary dynamics and measurements—provide a powerful framework for understanding open quantum systems. Beyond their ensemble averages, these trajectories can exhibit rich and distinctive behaviors. A striking example is the measurement-induced phase transition, where pure states conditioned on specific measurement outcomes display sharp entanglement transitions. However, experimentally probing such effects has remained challenging due to the exponential cost of post-selecting specific trajectories. In this talk, I will introduce a deterministic and efficient method to prepare selected trajectories using imaginary-time evolution. This approach applies to a broad class of states and opens the door to experimentally exploring post-selection-dependent phenomena that were previously thought to be inaccessible.

Abastract: Quantum trajectories—individual realizations of a quantum system’s evolution under unitary dynamics and measurements—provide a powerful framework for understanding open quantum systems. Beyond their ensemble averages, these trajectories can exhibit rich and distinctive behaviors. A striking example is the measurement-induced phase transition, where pure states conditioned on specific measurement outcomes display sharp entanglement transitions. However, experimentally probing such effects has remained challenging due to the exponential cost of post-selecting specific trajectories. In this talk, I will introduce a deterministic and efficient method to prepare selected trajectories using imaginary-time evolution. This approach applies to a broad class of states and opens the door to experimentally exploring post-selection-dependent phenomena that were previously thought to be inaccessible.

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Host: Dr. Matthew Liska

Title: Quasi-periodic Eruptions

Abstract: Quasi-Periodic Eruptions (QPEs) are a newly discovered type of recurring X-ray transient originating from supermassive black holes (SMBHs) in nearby, low-mass galaxy nuclei. They are thought to be the first observed counterparts to extreme mass-ratio inspirals (EMRIs), a long-anticipated gravitational wave source class detectable by future space-based interferometers (e.g. LISA). About a dozen QPEs are known, and in an unexpected twist, several of them have emerged from the nascent accretion disks formed by Tidal Disruption Events (TDEs). I will give an overview of the surprising discoveries, observational properties, and theoretical progress in QPEs since their discovery six years ago, including constraints on their emission mechanisms, prospects for probing EMRI orbital dynamics using QPE timings, and estimates of the QPE rate and their implication for EMRI formation. I will also briefly discuss ongoing work regarding the X-ray variability properties of TDEs as probes of their turbulent accretion flows, and electromagnetic study of evolutionary processes in ultracompact binary LISA sources, putting QPEs in the broader context of time-domain and multi-messenger astronomy.

Host: Dr. Itamar Kolvin

Title: The Fundamental Physics of the Onset of Frictional Motion: How does friction (or an Earthquake) start?

Abstract:

When two bodies are in contact, they are separated by an interface of sparse contacts. For the bodies’ motion (frictional motion) to initiate, these contacts have to be detached. We first show that this detachment process takes place by means of rapid singular cracks that propagate, at nearly sound speeds, within the interface. These cracks are akin to the earthquakes that enable contacting tectonic plates to slide. Their singular form, dynamics and arrest are well-described by the theory of fracture. We then describe how these rapid crack (earthquakes) are first formed; frictional motion starts via extremely slow, aseismic, nucleation fronts. We will then briefly develop a new theoretical description of this nucleation process that extends fracture mechanics. This theory quantitatively describes all experimentally observed features of the nucleation process and merges seamlessly with the accepted fracture mechanics description of rapid dynamic cracks. These results provide new understanding of the physics of friction, earthquake dynamics and even the more general question of ‘how things break’.
Reference:
[1] S. Gvirtzman, S., D. S. Kammer, M. Adda-Bedia, J. Fineberg. Nature 637, 369–374 (2025). https://doi.org/10.1038/s41586-024-08287-y.

Host: Prof. John Wise

Title: Ultralight to Heavy: Production Pathways of Axions and Dark Photons as Dark Matter

Abstract:

In this talk, I will review the motivation for axions (and alike particles) and dark photons as dark matter candidates. I will then briefly discuss some popular detection strategies in the ultralight mass regime.

Next, I will present two production mechanisms: freeze-in for the intermediate-to-high mass range, and misalignment plus parametric resonance for the ultralight regime. For both cases, I will highlight the favored regions of parameter space to account for the dark matter paradigm and the associated detection opportunities.

Host: Dr. Itamar Kolvin

Title: Experiments with Soft Interface Mechanics: Proteins, Plants, and Adhesive Contact

Abstract:

Surface and interfacial tensions play key roles in governing the mechanics of highly compliant materials, from traditional fluid capillary mechanics to the emerging field of elastocapillary mechanics of very soft solids. Our research group particularly studies the role of surface tension in soft interface mechanics, from driving surface instabilities and fracture on fluid surfaces to facilitating plant reproduction or competing with solid elasticity during adhesive contact. Our experiments combine mechanical manipulation with sensitive, high-speed 2D and 3D optical imaging to measure soft interface mechanics in both static and dynamic contexts. In this talk, I will discuss recently-discovered physical phenomena on fluid surfaces with adsorbed species, including Marangoni-driven, symmetric, star-shaped fracture on protein-laden fluid interfaces and the capillary multipole interactions harnessed by primitive land plants during their asexual reproduction. 

Title: Magnetic orders, stripes, and superconductivity - recent progress in computational studies of the Hubbard model

Host: Carlos Sa de Melo

Abstract: The Hubbard model has been a focal point of research in condensed matter physics, and more recently also in ultracold atoms. The physics of this model is often the outcome of a delicate balancing act between multiple competing or co-existing tendencies, which makes it highly challenging to determine. Robust predictions are difficult to obtain. Recently, significant progress has been made via advances in computational methods, and the combined use of complementary methods through collaborative efforts. I will share some of the lessons learned and insights gained, and what these computations have revealed about the properties of the Hubbard model. I will also discuss how these advances in computation can and are being applied to realistic strongly correlated electron systems. Many opportunities are rapidly emerging for synergy between computation and experiment, thanks to recent advances in cold atoms and in two-dimensional moire materials.

Short Bio: Shiwei Zhang is a Senior Research Scientist/Group Leader at the Center for Computational Quantum Physics (CCQ), Flatiron Institute, Simons Foundation. He is recognized as a world leader in computational quantum physics, known for broad contributions in computational algorithm innovations and developments, especially in Monte Carlo methods, and their applications. Methods he pioneered have been applied in diverse areas including in condensed matter physics, quantum chemistry, ultra-cold atoms, and nuclear physics. He has led a number of international collaborative teams on major research projects in computational quantum physics.

Zhang received his Ph.D in Physics from Cornell University. After three years of postdoctoral appointments, first at Los Alamos National Lab and then at Ohio State under an NSF postdoctoral fellowship, he joined the faculty of William & Mary, where he remained for over 20 years, holding the position of Chancellor Professor of Physics before he moved to Flatiron in 2018. He was recipient of multiple awards including an NSF CAREER award and the Cottrell Scholar Award. He is a Fellow of the American Physical Society.

Host:  Prof. Tamara Bogdanovic

Title: Variability of binary AGNs 

Abstract:

I will discuss recent results from numerical modeling of the electromagnetic (EM) variability signatures of accreting supermassive black hole (SMBH) binaries. Orbiting SMBH binaries produce both periodic, and stochastic, variability with potentially tell-tale signatures, especially in the shape of the power spectral distribution (PSD) of the optical continuum emission. Furthermore, the gravitational wave (GW) driven inspiral and merger of the two black holes can induce either of two types of “changing look” AGN events — Type-A events in which the AGN light is dimmest at the time of the merger, and Type-B events in which the AGN light is brightest around the merger time. The two types correspond to the direction of angular momentum flow between the binary orbit and the surrounding gas disk, and produce a correlated phase drifting in the LISA band, creating a new avenue for multi-messenger (EM+GW) study of binary black holes with e.g. LSST and LISA.

Host: Prof. Hailong Wang 

Title: Longitudinal Spin Pumping in a Magnetic Phase Transition

Abstract: A particle current generated by pumping in the absence of gradients in potential energy, density or temperature is associated with non-trivial dynamics. A representative example is charge pumping that is associated with the quantum Hall effect and the quantum anomalous Hall effect. Spin pumping, the spin equivalent of charge pumping, refers to the emission of a spin current by magnetization dynamics. Previous studies have focused solely on transversal spin pumping arising from classical dynamics, which corresponds to precessing atomic moments with constant magnitude. However, longitudinal spin pumping arising from quantum fluctuations, which correspond to a temporal change in the atomic moment’s magnitude, remains unexplored. Here we experimentally investigate longitudinal spin pumping using iron–rhodium (FeRh), which undergoes a first-order antiferromagnet-to-ferromagnet phase transition during which the atomic moment’s magnitude varies over time [1]. By injecting a charge current into a FeRh/platinum bilayer, we induce a rapid phase transition of FeRh in nanoseconds, leading to the emission of a spin current to the platinum layer. The observed inverse spin Hall signal is about one order of magnitude larger than expected for transversal spin pumping, suggesting the presence of longitudinal spin pumping driven by quantum fluctuations and indicating its superiority over classical transversal spin pumping. Our result highlights the significance of quantum fluctuations in spin pumping and holds broad applicability in diverse angular momentum dynamics, such as laser-induced ultrafast demagnetization, orbital pumping and quantum spin transfer. If time permits, we will also discuss the magnetic octupole Hall effect in d-wave altermagnets [2].

[1] T. Lee et al., Nature 638, 106-111 (2025).

[2] H.-W. Ko and K.-J. Lee, arXiv:2508.00794 (2025).

Host:  Dr. Surabhi Sachdev

Title: Facilitating Multi-Messenger Astrophysics with Timely Information about Gravitational Waves

Abstract:

In the age of multi-messenger astrophysics, providing timely information about gravitational-wave events is vital to achieve coincident detections. Electromagnetic counterparts to gravitational waves originating from compact binary coalescences containing at least one neutron star can help answer unsolved questions in physics such as the rate of expansion of the universe and the neutron star equation of state, describing how matter behaves in extreme densities. Rapid PE is a parallelized Bayesian parameter estimation scheme designed to facilitate these follow-up observations by quickly estimating parameters such as the component masses of these binaries with gravitational waves detected by the LIGO-Virgo-KAGRA (LVK) collaboration. In this seminar, I will present our results on the use of this method to provide reliable source classification updates for binary black hole (BBH), binary neutron star (BNS), and neutron star-black hole (NSBH) mergers within a few minutes of detection.

Host:  Julia Speicher

Title: Understanding the dynamics of accretion onto black holes in radiation GRMHD simulations

Abstract:

Radiation and magnetic fields play crucial roles in shaping the physics of black hole accretion, especially in near- and super-Eddington regimes. To model this process, we solve the GRMHD equations coupled with angle-dependent radiation transfer, which enables us to capture the complex dynamics driven by radiation and magnetic fields in extreme environments. In the super-Eddington regime, the accretion disk thermally expands under radiative support, forming a narrow conical funnel through which radiation escapes, resulting in low radiation efficiency. In the near-Eddington regime, the disk structure strongly depends on the magnetic field topology, allowing the system to reach a steady state as either a thin disk with magnetic coronae or a magnetically elevated disk.  These simulation results align with several observational findings and provide predictive diagnostics for future observations, which I will further elaborate on in the talk. 

Host: Prof. JC Gumbart

Title: Bayesian Frameworks for Understanding Conformational Heterogeneity in Cryo-EM Data.

Abstract:

In the past decades, technological advancements in experimental and computational approaches, such as nuclear magnetic resonance (NMR) spectroscopy, cryo-electron microscopy (cryo-EM), machine learning (ML), and molecular dynamics (MD) simulations, have revolutionised structural biology. They provide comprehensive information into the structural dynamics of biomolecules, allowing scientists to unravel the complex relationships between molecular structural dynamics and biological function with unprecedented precision. This talk presents my Bayesian approach for extracting conformational heterogeneity from cryo-EM data. It uses the cryo-EM images to reweight a given conformational ensemble generated by an MD simulation. The reweighted ensemble approximates the biomolecule's free energy landscape, offering a physical interpretation of conformational heterogeneity in cryo-EM data. Nonetheless, this approach requires evaluating the image-to-structure likelihoods for thousands of cryo-EM images to dozens of structures, which can be computationally demanding. To extend the scalability and applicability of the Bayesian approach, I developed CryoLike, a Python package with GPU acceleration for evaluating the image-to-structure likelihood efficiently and robustly. Lastly, I present an application of the developed tools in extracting the free energy landscape from an experimental cryo-EM dataset of a flexible biomolecule.

Host: Prof. Hailong Wang

Title: Controlling and probing quantum correlations in superconducting circuits

Abstract: Superconducting circuits provide a versatile platform for exploring many-body physics in synthetic quantum matter. To advance scalable quantum simulation using circuit devices, I will present our recent progress in developing efficient techniques for controlling and measuring quantum correlations and dynamics. We engineer tunable driven-dissipative baths and apply them in coupled superconducting qubit arrays to autonomously stabilize entangled states. Additionally, we investigate how collective qubit decay can be harnessed and combined with coherent control to generate quantum correlations in qubit lattices. To characterize the resulting quantum states, I will show our new methods to measure in-situ particle current and perform site-resolved tunneling spectroscopy. We apply these tools to probe quantum transport and phase transitions in a circuit Bose-Hubbard lattice.

Short bio: Alex Ruichao Ma received his Ph.D. in Physics from Harvard University in 2014, where he studied many-body physics using ultracold atoms in optical lattices. From 2015 to 2019, he worked on superconducting qubits for quantum simulation as a Kadanoff-Rice Postdoctoral Fellow at the James Franck Institute, University of Chicago. In 2019, Alex joined Purdue University as an Assistant Professor in the Department of Physics and Astronomy. His experimental group focuses on quantum many-body physics and quantum information science using superconducting circuits. He is a recipient of the NSF CAREER Award in 2022.

Host: Prof. John Wise

Title: The Origin of Supermassive Black Holes from Pop III.1 Seeds

Abstract: 

The origin of supermassive black holes (SMBHs) is a key open question for contemporary astrophysics and cosmology. Here we discuss the predictions of a model of SMBH formation from Pop III.1 protostars, i.e., metal-free stars forming in locally isolated dark matter minihalos, where dark matter annihilation has a chance to alter the structure of the star allowing growth to supermassive scales (Banik, Tan & Monaco 2019; Singh, Monaco & Tan 2023; Cammelli et al. 2025). The model predicts that all SMBHs form very early in the Universe (within a few 100 Myr, i.e., by z ~ 20) with a spatial distribution that is initially relatively unclustered. We also present predictions for SMBH occupation fractions, host galaxy properties, frequency of binary SMBHs and the gravitational wave background from this SMBH population. These predictions are compared to latest results from the Hubble Space Telescope, James Webb Spact Telescope and pulsar timing array observations.

Host:  Prof. Laura Cadonati

Title: Probing the inner geometry of AGN accretion flows and searching for SMBHB candidates in large optical sky surveys

Abstract:

Observations of the AGN Fairall 9 with NICER and Swift revealed a strong relationship between the flux of the UV continuum and the X-ray soft excess, indicating the presence of a “warm” Comptonized region which may act as a second reprocessor between the “hot” X-ray corona and the accretion disk. This has previously been suggested as an explanation for the weak X-ray/UV correlation observed in many AGN, and it can be confirmed using NICER's unprecedented spectral coverage of X-ray variability on timescales of days to years. Our separate NICER reverberation mapping campaign on the AGN NGC 7469 provides no evidence for a warm corona, suggesting that there is no uniform prescription for the geometry of the inner accretion flow across all AGN. In this seminar, I will present the X-ray spectral modeling results from both AGNs in the context of understanding their geometries and energetic properties. I will also discuss the Null-Signal Template (NST) method, a new data-driven approach to testing the significance of possible periodic signals in quasar light curves. NST employs Bayesian statistics to differentiate between supermassive black hole binary (SMBHB) signals and the complex noise of individual quasars. I will share new tests on the validity of the NST method using simulated LSST-like light curves and discuss the prospects for the application of NST to SMBHB detection in both existing and upcoming quasar surveys.

Host: Prof. Tamara Bogdanovic

Title: The Growth and Evolution of SMBHs via Galaxy Mergers

Abstract:
After decades of SMBH observations, the connection between AGN triggering and galaxy mergers remains incomplete, although AGN are likely key players in the evolution of massive galaxies. Theoretically, there are many reasons to expect a link between galaxy mergers and the accretion of material onto at least one of the central supermassive black holes. Yet, observationally, varied results have led to uncertainty in whether AGN triggering is dependent on the environment. One of the best ways to analyze the possible ties between merger environments and SMBH activity is to study systems with unique observational flags of merger-driven SMBH growth -- or, dual AGN. I will present my work quantifying the dual AGN fraction at both high redshift, and as a function of redshift, via a large and uniform study of dual AGN in X-rays, up to z=3.5.  By analyzing available data in wide and deep public Chandra surveys, the dual AGN fraction at both the high-redshift (2.5 < z < 3.5) and low-redshift (z < 0.03) regime can be better constrained. Pairing X-ray results with available multi-wavelength data (WISE, HST), we gain insight on how the X-ray activity of interacting AGN depends on their environments. Lastly, I will highlight the capabilities of future high spatial-resolution X-ray observatories, which will revolutionize the field of dual AGN detectability, and our understanding of the role mergers play in AGN triggering.

Host: Dr. Matthew Liska

Title:Title: Thermonuclear X-ray Bursts in the NICER Era

Abstract: 

Thermonuclear X-ray bursts are sudden flashes observed from some low-mass X-ray binaries. Time-resolved spectral analysis and long-term observations have revealed that they occur due to the unstable thermonuclear burning of the accreted matter on the surface of the neutron star. They typically last a few tens of seconds, and the recurrence of these events seems to track the amount of matter accreted. Observations of thermonuclear X-ray bursts provide a wealth of information about thermonuclear burning, accretion physics, and the properties of the host systems, while also playing a crucial role in measurements of neutron star masses and radii. In this talk, I will focus on X-ray burst observations with the Neutron Star Interior Composition Explorer (NICER) since its launch in 2017. With its large effective area in the soft X-ray band, NICER has allowed us to probe the interaction of X-ray bursts with their surroundings in a systematic way for the first time. I will summarize our findings on the excess soft X-ray emission observed during the bursts and how it can be interpreted in terms of changes in the mass accretion rate during the bursts and/or the reflection of the X-ray burst emission off the accretion disk.

Host: Prof. Uzi Landman

Title: Moiré Physics in Graphene Layers – What’s the “Magic”?

Abstract: The unexpected discovery of superconductivity and strong electron correlation in twisted bilayer graphene, a system composed solely of 𝑠-𝑝 electrons, stands as one of the most intriguing developments in two-dimensional materials in recent years. A key feature of this system is the emergence of flat energy bands near the Fermi level (a condition that promotes the formation of novel many-body phases) at the so-called “magic angles.” Gaining a deeper understanding of the physical origin of these flat bands is essential for constructing an effective theory of unconventional electron correlation. In this talk, I will present our recent theory on the origin of these magic angles in twisted graphene layers and their connection to the Fermi ring in AA-stacked multilayer graphene.

Host: Dr. Matthew Liska

Title: Dust Scattering Halo of black hole binary 4U 1630-47 Observed with Chandra and APEX: Using mm and X-ray Imaging to Constrain Source and Molecular Cloud Distances

Abstract: 

Dust scattering halos have been utilized to study spectral variations during eclipses, physical properties and distribution of dust grains in the interstellar medium (ISM), X-ray extinction, and source distance determination using X-ray flux evolution and radial distribution of X-ray rings. We have obtained a Chandra image of the dust scattering halo of 4U 1630-47 and used it together with low-resolution 12CO images and determined the source to be 11.5 kpc in Kalemci et al. 2018.  We recently obtained very high-resolution mm images (12CO and 13CO) with the Atacama Pathfinder Experiment (APEX)  of the region. We used machine learning tools to obtain a 3-dimensional mapping of clouds in the line of sight, however, the clouds could be at their near, or far distance estimates based on their radial velocities. We generated many halo images placing the clouds at near and far distances and compared them with the actual halo image to constrain not only the source distance but also the distribution of molecular clouds in the line of sight. This method has the potential to constrain distances to compact objects behind large column densities for which the traditional methods might fail. 

Host: Prof. Zhu-Xi Luo

Title: Thermalization rates and anomalous relaxation from operator hydrodynamics

Host: Prof. Tamara Bogdanovic

Title: Probing neutron star physics via multimessenger astronomy

Abstract: 

In this talk I will review recent work that allowed us to obtain a better understanding of the neutronstar equation of state and neutron star properties by use of multimessenger observations of (binary) neutron stars.I will also discuss recent and current efforts of modeling binary neutron stars mergers that will help enable constraints on the unknown finite temperature nuclear equation of state by use of third generation gravitational wave observatories.

Host: Prof. Laura Cadonati / Dr. Surabhi Sachdev

Title: The anti-aligned spin of GW191109: Glitch Mitigation and its Implications

Abstract: 

Abstract: One of the most interesting events in the third LVK observing run was GW191109, which was found to have spins which were confidently anti-aligned with the orbital angular momentum - one of only two such cases which has been released - and high masses. This implies GW191109 may be of dynamical origin, making it our first probe of this formation channel. However, GW191109 was coincident with a transient noise source known as a "glitch," which may affect these conclusions dramatically. I will discuss the origins and modelling of the glitch in question, and work I have done to fully characterize the astrophysical properties of GW191109 in the presence of this glitch. If time allows I will also discuss additional aspects of glitch modeling, and statistical tests to identify the impact of glitches on parameter estimation.

Bio:

Rhiannon is a fifth year graduate student at Caltech studying gravitational wave astrophysics, and a member of the LIGO-Virgo-Kagra collaboration. As an undergraduate she attended Georgia Tech, where she did research with Laura Cadonati and Deirdre Shoemaker on the inference of compact binary source properties. At Caltech she joined the LIGO Lab and is advised by Alan Weinstein. Much of her work has focused on modeling glitches in the LIGO detectors, understanding how glitches impact the inference of source properties, and developing techniques to mitigate them. Additionally, she has done substantial work on the development of data management infrastructure for the LVK collaboration, and the preparation of the forthcoming gravitational wave transient catalogs.

Host: Prof. John Wise

Title: Galaxy Evolution and the Cosmic Baryon Cycle in 3D

Abstract: 

Galaxies are intricately linked to the gas in and around them, making the characterization of gas flows essential for directly constraining star formation, gas flow rates, and feedback processes, as well as for testing modern theories of galaxy evolution. The recent deployment of highly sensitive integral field units (IFUs) on large telescopes, such as the Keck Cosmic Web Imager (Keck/KCWI), has provided a novel 3D perspective to probe this diffuse gas. In this talk, I will present recent findings from the KBSS-KCWI and CIRAS surveys. The KBSS-KCWI survey, a ~200-hour program utilizing KCWI, aims to understand the nature of Lyα emission around star-forming galaxies at cosmic noon. Through realistic radiative transfer modeling, we have found that CGM Lyα emission is consistent with resonant scattering in a clumpy medium powered by central ISM emission. Meanwhile, the ongoing CIRAS (Comprehensive IFU Research on Accurate Abundance Studies) survey uses the newly commissioned KCWI red channel, alongside Herschel, SOFIA, and JWST data, to construct a reference sample that establishes an accurate abundance scale in star-forming regions throughout cosmic history. 

Host: Prof. JC Gumbart

Title: Understanding the thermodynamics of lipid phase separation using molecular simulations.

Abstract:

Phase separation occurs in multiple parts of cells, including the cell membranes, where the so-called ``lipid raft'' hypothesis posits the formation of ordered domains floating in a sea of disordered lipids. The resulting lipid domains often have functional roles. However, the thermodynamics of lipid phase separation and their resulting mechanistic effects on cell function and dysfunction are poorly understood. Understanding such complex phenomena in cell membranes, with their diverse lipid compositions, is exceptionally difficult. For these reasons, simple model systems that can recapitulate similar behavior are widely used to study this phenomenon. Despite these simplifications, the time- and length-scales of domain formation pose a challenge for molecular dynamics (MD) simulations. Thus, most MD studies focus on spontaneous lipid phase separation --- essentially measuring the sign (but not the amplitude) of the free energy change upon separation --- rather than directly interrogating the thermodynamics.  We have developed a set of techniques to extract the free energy change upon phase separation directly from molecular dynamics simulations. In addition to a number of validation studies, we have used these methods to determine the simulation size needed to recapitulate the thermodynamics of membrane phase separation. 

Host: Dr. Surabhi Sachdev

Title: Gravitational waves: from black holes to the cosmos

Abstract: 

Gravitational waves reveal the universe through an entirely unique spectrum, complementary to electromagnetic and neutrino observations. Although the field is young, it has already revolutionized our understanding of black holes and neutron stars, with implications for gravity, stellar and galactic astrophysics, nuclear physics and cosmology. In this talk, I will review some of these results with a focus on black hole mergers—currently the most abundant source of gravitational waves. I will outline the astrophysical puzzle of heavy black-hole mergers, and their use to study physics and cosmology. This is an exciting, observationally-driven field with abundant open questions, which will continue to grow in the following decades thanks to new and improved instruments. With the right analysis tools and theoretical foundation, the potential for discovery is unprecedented.

Host: Harold Kim

Title: It's all about mass

Host: Prof. John Wise

Title: JWST's Little Red Dots: Masters of Disguise in the High-Redshift Universe 

Abstract: 

This talk will explore the exciting journey to probe several populations of black holes, spanning from the distant to the local Universe. I will focus primarily on the "little red dots" (LRDs), a newly discovered and puzzling population of compact red sources at redshift z > 4, identified by JWST. These objects challenge our current astrophysical models in several ways. First, I will discuss the detection of overmassive black holes relative to the stellar mass of their host galaxies. Second, I will address the X-ray weakness problem, where these sources remain undetected in deep X-ray surveys. I will use advanced GRRMHD simulations to show how mildly super-Eddington accretion onto slowly spinning black holes can resolve this issue. Third, I will explore the extremely high stellar densities at the cores of these objects and their potential for triggering runaway stellar collisions. Throughout the talk, I will also discuss how the LRDs represent a perfect bridge to study other populations of black holes, with a focus on the role of future observatories such as HWO and AXIS. These include the search for black hole seeds at redshifts z = 20-30 and the detection of quiescent black holes in the local Universe.

Host: Predrag Cvitanovic/ Noel Dudeck

Title:  Reasoning about Graphs with Large Language Models

Abstract: Graphs are a powerful tool for representing and analyzing complex relationships in real-world applications. Large Language Models (LLMs) have demonstrated impressive capabilities by advancing state-of-the-art on many language-based benchmarks. Their ability to process and understand natural language open exciting possibilities in various domains. Despite the remarkable progress in automated reasoning with natural text, reasoning on graphs with LLMs remains an understudied problem that has recently gained more attention. This talk builds upon recent advances in expressing reasoning problems through the lens of tasks on graph data. We will provide an in-depth discussion of techniques for representing graphs as inputs to LLMs, as well as some theoretical limits to the ability of transformers to solve various graph tasks.

Bio: Jonathan Halcrow is a Ramblin Wreck from Georgia Tech, completing his undergraduate studies at GT in 2003 and Physics PhD in 2008, studying under Predrag Cvitanovic. His thesis covered the topic of turbulence in Plane Couette flow. More recently, he has been working as a Software Engineer at Google since 2013, as part of the Graph Mining team in Google Research in Atlanta. His research at Google covers the topics of approximate nearest neighbor search, graph neural networks, and improving the abilities of large language models to reason about structured data.

Host: Zeb Rocklin

Title: Acoustically Levitated Granular Matter

Abstract: An intense ultrasound field can be used not only to levitate particles and manipulate their positions, but sound scattered off individual solid objects gives rise to tunable forces that acoustically bind the particles into larger aggregates. For levitation in air, furthermore, the small viscosity makes it possible to explore the regime of underdamped dynamics in a strongly coupled multi-particle system far-from-equilibrium. I will discuss recent experiments that exploit acoustic levitation to self-assemble small particles into monolayer rafts freely floating in air, while tracking their dynamics with high-speed video imaging. By changing the interparticle spacing and controlling the acoustic energy density, the rafts can transform from close-packed solids into soft lattices that can ‘melt’ into 2D liquids and eventually expand into 3D particle swarms. Along the way, acoustically levitated granular matter provides an exciting new platform to study non-reciprocal multibody forces and the emergent dynamical behavior they can generate.

Bio: Heinrich Jaeger is the Sewell Avery Distinguished Service Professor of Physics at the University of Chicago. He received his Ph.D. in physics in 1987 from the University of Minnesota and has been on the faculty at U Chicago since 1991, directing the Chicago Materials Research Center from 2001 – 2006, and the James Franck Institute from 2007-2010. Jaeger’s current research focuses on self-assembled nanoparticle-based structures, on the rheology of concentrated particle suspensions, and on studies of the flow and jamming properties of granular materials.

Host: Gongjie Li

Title: Planets are not Points: Structure Evolution and Dynamical Evolution are Intertwined

Abstract: 

The two subfields of planetary structure evolution and planetary dynamics are two rich and complex fields that have advanced in lockstep, but independently of one another. I will discuss how accounting for minor interior structure evolution of a planet can have a profound impact on its dynamics and the architecture of the resulting system. Using full N-body simulations, I present a detailed case study of the HAT-P-11 system, which is a bizarre system with two misaligned, eccentric planets. I show that a combination of planet-planet scattering and Kozai-Lidov migration is capable of reproducing the present-day configuration of the system, but ONLY if these minute structure effects are accounted for.

Host: Prof. Tamara Bogdanovic

Title:  Gravitational Wave and Electromagnetic Signals Associated with the Tidal Disruption of White Dwarfs

Abstract: 

I will discuss the gravitational-wave and electromagnetic signals expected to accompany the tidal disruption of a white dwarf by a massive (i.e., “intermediate mass” black hole). Since white dwarfs are very compact, they can only be disrupted outside of the horizon of a black hole that less massive than about 105 M⦿ (if it is not spinning; up to 106 M⦿, if it is maximally spinning). As such, their disruptions can serve as signposts of black holes in this intermediate mass range.  The gravitational wave signal from the disruption of a white dwarf in an unbound orbit is a brief burst while the optical spectroscopic signature of such an event is arguably unique and can be used to identify it. Things get more interesting if the white dwarf is captured in a bound orbit before it is disrupted. Such encounters are likely the most common type of an extreme mass ratio inspiral. In such a scenario, the gravitational wave signal is a “slow chirp” that traces the gradual decay of the orbit, it can last for months to years, and is detectable by LISA. Therefore, observers will have ample advance warning to get ready to catch (quasi-)periodic electromagnetic emission that may precede the disruption and the electromagnetic flare that accompanies and follows the disruption. 

Host: Dan Goldman

Title: Propulsion and interaction of wave-propelled interfacial particles

Abstract: When an asymmetric floating body is internally or externally vibrated, the self-generated capillary wavefield can lead to steady propulsion or rotation.  In this talk, I will discuss several related and recently discovered systems that leverage this driving mechanism.  On a vibrating fluid substrate, freely floating particles are shown to self-propel along straight paths, rotate in place, or move along curvilinear trajectories, depending sensitively on the particle asymmetries and driving parameters. Such particles interact at a distance through their mutual wavefield, and exhibit a rich array of multi-body dynamics.  I will also present our work on the "SurferBot": a centimeter-scale robotic device that self-propels along a fluid interface using an onboard vibration motor.  Overall, these highly accessible and tunable macroscopic systems serve as a novel platform for exploring active and driven matter interacting in fluid environments.

Bio: Daniel M. Harris is an Associate Professor of Engineering at Brown University in the Fluids and Thermal Sciences group. Before joining Brown, Dan was a Postdoctoral Research Associate and Lecturer at the University of North Carolina at Chapel Hill in the Department of Mathematics.  Dan received his B.S. in Mechanical Engineering.

Host:   Itamar Kolvin

Title: Transport of nanoparticles and viruses through crowded, complex fluids

Abstract: 

Transport of nanoparticles affects applications ranging from targeted drug delivery to point-of-care diagnostics to processing of nanocomposite materials. In each of these applications, nanoparticles must be transported through a complex fluid to reach the desired target, whether a cancerous tumor, a membrane, or a polymer melt. For large particles, the surrounding medium is effectively homogeneous across the surface of the particle, so that the transport properties can be directly related to the bulk fluid properties. For nanoparticles, however, the particle size is comparable to the length scales of heterogeneities in the fluid so that the particle dynamics decouple from bulk properties and are poorly understood. Here, we combine microscopy and scattering experiments with molecular simulation to investigate how nanoparticles transport through polymer solutions, which serve as a tunable model of viscoelastic liquids, and examine how the dynamics of the nanoparticles are coupled to relaxations of the surrounding liquid. I will focus on our recent work probing transport of viruses through solutions of synthetic and natural charged polymers, where the macromolecular structure differs from that of neutral polymers due to the presence of charges along the polymer backbone. The physics elucidated in these studies will grant better control over the transport and dispersion of nanoparticles through complex, heterogeneous materials.

 Host: Surabhi Sachdev/Laura Cadonati

Title: A sparkle in the dark: data intensive searches for Dark Matter with LUX-ZEPLIN

Abstract: The nature and origin of dark matter are among the most compelling mysteries of contemporary science. There is strong evidence for dark matter from its role in shaping the galaxies and galaxy clusters that we observe in the universe. Still, physicists have tried to detect dark matter particles for over three decades with little success.

This talk will describe the leading effort in that search, the LUX-ZEPLIN (LZ) experiment. LZ is an instrument that is superlative in many ways. It consists of 10 tons of liquified xenon gas, maintained at almost atomic purity and stored in a refrigerated titanium cylinder a mile underground in a former gold mine in Lead, South Dakota. In 2022, the LZ collaboration released its initial dark matter search results, achieving world-leading sensitivities to a wide range of potential dark matter candidates.

LZ is in the process of accumulating a massive dataset of many petabytes of data and record several billions of particle interactions, only a handful of which might be produced by dark matter interactions. Identifying such interactions requires leveraging advanced detector design and state-of-the-art machine learning algorithms. The talk will present the challenges in constructing this large-scale underground experiment and interpreting its data, along with the prospects LZ presents for finally discovering the dark matter particle.

Bio: Maria Elena Monzani is a dark matter data wrangler. Her research field is Astroparticle physics, which focuses on topics at the intersection between particle physics and astrophysics/cosmology, using the tools of data-intensive science. She received a dual Ph.D. from the University of Milano and the University of Paris 7, performing research with the Borexino experiment that measured neutrinos produced by the Sun. She then held a postdoctoral position at Columbia University before joining SLAC in 2007 to work on the Fermi Gamma-ray Space Telescope. Today, Monzani is a lead scientist at SLAC and a senior Kavli Institute for Particle Astrophysics and Cosmology member at Stanford. She leads the software computing effort for the LZ Dark Matter Experiment and the science operations team for the Fermi satellite. She is also an Adjunct Scholar at the Vatican Observatory and enjoys discussing the shared philosophical foundations of scientific and religious endeavors.

SoP Colloquium-20240909_153228-Meeting Recording.mp4

Host: Tamara Bogdanovic

Title:  Electromagnetic and multi-messenger searches for supermassive black hole binaries

Abstract: 

Supermassive black hole binaries are thought to be an inevitable product of the prevailing galaxy evolution scenarios where most massive galaxies host a central black hole and undergo mergers over cosmic time. The early stages of this process have been observed in the form of interacting galaxy pairs and widely separated dual quasars, but the close, gravitationally bound binaries that are expected to follow have proven elusive. The detection of this population is important because at the smallest separations they become bright sources of low-frequency gravitational waves and are prime targets for multi-messenger detections with pulsar timing arrays (PTAs) and the upcoming Laser Interferometer Space Antenna (LISA). In this talk, I will discuss observational signatures of binary supermassive black holes and prospects for multi-messenger detections with electromagnetic facilities and gravitational wave detectors.

Bio:

Jessie Runnoe is an assistant professor of Physics and Astronomy at Vanderbilt University. She is a graduate of Whitman College, received her PhD in physics from the University of Wyoming in 2013, and held postdoctoral research positions at Penn State and the University of Michigan. Her research is focused on growing supermassive black holes, which we view as quasars. To do this work, she uses space telescopes like the Hubble Space Telescope and big-data surveys of large areas of the sky (including time-domain surveys, which show a movie of the sky instead of a single image) taken with ground-based optical telescopes. In her free time, she is an avid cyclist and ascribes to the belief that the correct number of bikes to own is N+1, where N is the number of bikes you currently own.

Host: Matthew/ Nepomuk

Title: The inner workings of pulsar magnetospheres 

Abstract: Pulsars are rotating magnetized neutron stars that emit repeating pulses of radiation spanning all of the electromagnetic spectrum. 55 years after their discovery more than 2000 pulsars are known, and they have been used as probes of diverse phenomena ranging from the properties of interstellar medium to the predictions of general theory of relativity. Despite great observational successes, our theoretical understanding of how pulsar magnetospheres work is incomplete. Pulsars bring together aspects of classical and quantum electrodynamics, coupled with strongly magnetized plasma physics in curved rotating spacetime of a massive compact object. The nonlinear interplay of these effects makes it a difficult but rewarding problem to study. I will review the status and progress of pulsar modeling, culminating with recent developments in fully kinetic simulations of pulsar magnetospheres. These simulations allow us to find the shape of the magnetosphere and the location of particle acceleration regions, constraining the origin of high energy and radio emission. The pulsar magnetosphere is a prototype for other strongly magnetized astrophysical objects, and I will discuss how the lessons from pulsar modeling can be useful in understanding the physics of black hole magnetospheres and in predicting electromagnetic counterparts to gravitational wave sources.

Host: Itamar Kimchi

Title: TBA

Host: Ignacio Taboada 

Title: The Tokai to Kamioka Experiment

Abstract: Neutrinos are a tiny subatomic particle with surprising properties under active study. In particular, neutrinos oscillate, that is, they convert from one type of neutrino to another, is a surprising phenomenon under active study. The origin of neutrino mass is important for astrophysics, cosmology and particle physics, and many open questions surrounding neutrino oscillation exist. The Tokai-to-Kamioka (T2K) neutrino oscillation experiment sends a beam of muon flavor neutrinos or antineutrinos 295km across Japan. This colloquium will talk about the wonderful world of neutrinos, the surprising landscape of neutrino oscillation, through the lens of recent activities on T2K, and toward the future, global neutrino exploration of neutrinos.

Bio: Kendall Mahn is currently an Associate Professor at MSU in the Department of Physics and Astronomy. She received her B.Sc. degree in Physics from MIT and wrote her undergraduate thesis on extragalactic neutrinos in Super-Kamiokande. Her 2009 Ph.D. dissertation Columbia University was on a search for muon neutrino and antineutrino disappearance due to sterile mixing with the MiniBooNE experiment. As a postdoctoral research fellow at TRIUMF, she served in multiple leadership roles on the Tokai-to-Kamioka neutrino oscillation experiment, including oscillation analysis convener. Mahn is now the T2K International Co-spokesperson and has also held leadership roles on the future Deep Underground Neutrino Experiment (Calibration Consortium technical lead). She served on the 2023 P5 committee. She was a 2016 Alfred P. Sloan Research Fellow and a 2016 Fundamental Physics Breakthrough Prize Laureate.

Host: Dr. Matthew Liska

Title: Exploring hydrogel dynamics and a pore forming toxin structure via molecular dynamics simulations

Abstract: 

"Classical" accretion disks are geometrically thin, radiatively efficient and mechanized by turbulent viscosity. Yet, many observational and theoretical issues challenge this paradigm, especially in quasars. This is perhaps unsurprising, as classical disks do not take into account certain key physics. For instance, the infalling gas that eventually forms a disk around a black hole has no prior knowledge of the black hole spin axis. Thus, most accretion disks will be at least initially misaligned with respect to the black hole spin axis. As the black hole rotates, it drags the surrounding space-time, inducing 'Lense-Thirring' torques which cause the disk to undergo precession and become warped. This can drastically alter the accretion process and drive rapid variability, similar to that which is seen in changing-state active galactic nuclei. Additionally, quasars are generally fed from cold, highly magnetized gas complexes, which determines the initial conditions of the disk. This can result in a disk that is magnetically dominated, enabling high accretion rates that are sometimes above the Eddington limit, which has important consequences for the inner accretion flow. In this talk,  I will discuss my recent work on both radiative and non-radiative general-relativistic magnetohydrodynamic simulations of both thin, highly tilted accretion disks and super-Eddington, highly magnetized disks around rapidly rotating black holes. In the former case, I will present novel dissipation mechanisms unique to these systems that drive accretion on timescales much shorter than the usual viscous time. In the latter case, I will discuss the physics that governs the magnetic state of the disk, the resulting emission and outflow properties, and the implications for the cosmological growth of supermassive black holes. 

Host: Prof. Chunhui Du

Title: Inside Nature Materials: An Editor’s Perspective

Abstract: Nature Materials offers authors high visibility for their work. A team of full-time, professional editors select and commission articles that represent a substantial and arresting fundamental, mechanistic, methodological or practical advance. In this talk I will convey the editor’s perspective on the life of a manuscript after submission to Nature Materials, and provide an overview of the types of content that we publish.

Bio: “Daniel McNally received a BSc in Physics and Astrophysics from University College Cork and a MSc in Physics from Trinity College Dublin in Ireland. He earned his PhD in Physics at Stony Brook University and Brookhaven National Laboratory focusing on strongly correlated materials, with a particular emphasis on neutron scattering. He continued to work on quantum materials using resonant inelastic x-ray scattering as a postdoctoral researcher at the Paul Scherrer Institut, Switzerland. At Nature Materials, which he joined in March 2018, Daniel handles manuscripts in correlated electron systems, topological materials and spintronics. Daniel is currently based in the New York office.”

Host: Prof. JC Gumbart

Title: Exploring hydrogel dynamics and a pore forming toxin structure via molecular dynamics simulations

Zoom link: https://gatech.zoom.us/j/93674602425?pwd=LTUW4eCaki8QSeRvFJ6Yg6wlNKUDbp.1

Meeting ID: 936 7460 2425

Passcode: 334119

Abstract:

Adaptable hydrogels crosslinked by reversible bonds provide an ideal cell culture environment mimicking the highly dynamic extracellular matrix. Combining molecular dynamics (MD) simulations, adaptive biasing force as well as kinetic Monte Carlo calculations, we model a cell-adaptable hydrogel formed by hyaluronic acids grafted with either adamantane or cholic acid via cyclodextrin-based host-guest complexation. Our calculations pinpoint the critical role of host-guest binding kinetics in dictating the timescale of network reorganization in the supramolecular hydrogel and reveal that by matching this timescale with that of cellular activities one can design dynamic hydrogels that support efficient 3D cell spreading. More recently, our simulations of hydrogels with interface dynamics-induced network reconfiguration (DNR) further revealed how tuning mold dynamics through silicon chain grafting enabled effective manipulation of the wettability of the DNR hydrogel, transforming its otherwise hydrophilic surface into a hydrophobic one. In addition, I will discuss our most recent modelling of the pore forming toxin VacA from Helicobacter pylori. 

Education

Ph.D., Harvard University, Physics, 2014

A.M., Harvard University, Physics, 2009

B.S., California Institute of Technology, Mathematics, 2007

La Crosse Central High School, La Crosse, WI, 2003

Host: Prof. JC Gumbart

Zoom link: https://gatech.zoom.us/j/93533796005?pwd=bWowYWRGNGROdi9RYzlOdTJjMGJiQT09

Meeting ID: 935 3379 6005 / Passcode: 512281

Title: Accelerated Molecular Simulations: Methods and Applications

Abstract:

Remarkable advances of supercomputing and Artificial Intelligence are transforming computational chemistry and biology in studies of molecules to cells. However, large gaps remain between the time scales of supercomputer simulations (typically microseconds) and those of biological processes (milliseconds or even longer). To bridge these gaps, our research is focused on the development of novel computational methods and Deep Learning (DL) techniques, including Gaussian accelerated molecular dynamics (GaMD) and Deep Boosted Molecular Dynamics (DBMD). Our recently developed selective GaMD algorithms have unprecedentedly enabled microsecond atomic simulations to capture repetitive dissociation and binding of small-molecule ligands, highly flexible peptides and proteins, thereby allowing for highly efficient and accurate calculations of their binding free energies and kinetics. Moreover, the GaMD, DL and free energy prOfiling Workflow (GLOW) provides a systematic approach to predicting important molecular determinants and quantifying free energy profiles of biomolecules. In DBMD, probabilistic Bayesian neural network models are implemented to construct boost potentials that exhibit Gaussian distribution with minimized anharmonicity, which enables more accurate energetic reweighting and further enhanced simulations. Finally, we apply these new methods in advanced biomolecular modeling and computer-aided drug discovery. In collaboration with leading experimental groups, we combine complementary simulations and experiments to decipher functional mechanisms and design novel drug molecules of important biomolecules. Systems of our interest include membrane proteins such as G-protein-coupled receptors and membrane-embedded proteases, RNA-Binding Proteins and RNA.Remarkable advances of supercomputing and Artificial Intelligence are transforming computational chemistry and biology in studies of molecules to cells. However, large gaps remain between the time scales of supercomputer simulations (typically microseconds) and those of biological processes (milliseconds or even longer). To bridge these gaps, our research is focused on the development of novel computational methods and Deep Learning (DL) techniques, including Gaussian accelerated molecular dynamics (GaMD) and Deep Boosted Molecular Dynamics (DBMD). Our recently developed selective GaMD algorithms have unprecedentedly enabled microsecond atomic simulations to capture repetitive dissociation and binding of small-molecule ligands, highly flexible peptides and proteins, thereby allowing for highly efficient and accurate calculations of their binding free energies and kinetics. Moreover, the GaMD, DL and free energy prOfiling Workflow (GLOW) provides a systematic approach to predicting important molecular determinants and quantifying free energy profiles of biomolecules. In DBMD, probabilistic Bayesian neural network models are implemented to construct boost potentials that exhibit Gaussian distribution with minimized anharmonicity, which enables more accurate energetic reweighting and further enhanced simulations. Finally, we apply these new methods in advanced biomolecular modeling and computer-aided drug discovery. In collaboration with leading experimental groups, we combine complementary simulations and experiments to decipher functional mechanisms and design novel drug molecules of important biomolecules. Systems of our interest include membrane proteins such as G-protein-coupled receptors and membrane-embedded proteases, RNA-Binding Proteins and RNA.

Host: Dan Goldman

Atomic Physics: Lab to Market

I translated research performed at Georgia Tech and NIST into a product sold by my company Zerok NanoTech; this talk will detail the steps along the way. Topics will include: communication with lay audiences, licensing IP, filing patents, obtaining startup capital, identifying lead customers, and delivery of first products.

Host: Prof. Peter Yunker

Title: Evolutionary dynamics of non-motile cells growing on surfaces

Abstract:

Surface-associated microbial populations are ubiquitous in nature and display evolutionary dynamics that are not yet well characterized, despite their importance to human health and technology. Dense populations of non-motile microbes expand on surfaces by cell growth and division, while interacting mechanically with neighboring ones. In this talk, I will show that mechanical forces among proliferating cells reduce the power of natural selection in microbial colonies, prolonging the survival of deleterious mutations and reducing the rate at which beneficial mutations expand in these populations. These mechanical interactions also favor the maintenance of genetic diversity in colonies growing in time-varying environments. Additionally, I will present evidence that evolutionary adaptation can change the way in which cells interact mechanically with each other. By repeatedly propagating cells from the periphery of Saccharomyces cerevisiae colonies and using them to initiate new colonies, we have observed significant changes in cell shape and budding polarity, with cells becoming progressively more elongated with time. These adaptations lead to altered mechanical interaction between cells and may promote faster colony expansion. The evolutionary insights from our research may have implications for our understanding of pathogenic yeast strains, many of which are characterized by an elongated cell shape that is presumed to enhance their ability to infiltrate host tissues.

Host: Colin Parker

Title: Breakthroughs in epitaxial graphene electronics: semiconducting graphene and the spectacular edge state.

Abstract: Graphene electronics was conceived at Georgia Tech 22 years ago when the first graphene, devices were produced using graphene grown on silicon carbide substrates (so called epigraphene) [1], and the worlds’ first graphene electronics patent was filed[2]. The GT team has made steady progress since. Several years ago we noted that narrow graphene ribbons exhibited resistances that are always close to 26 k Ohms, which corresponds to the resistance quantum h/e2 where h is Planck’s constant an e is the charge of the electron, that turned out to be caused by a unique state at the edge of the ribbon. We have recently shown that this edge state does not involve an electron or a hole, which are the usual carriers of currents in graphene, but the carrier appears to be a combination of the two to form a zero-energy mode [3]. Moreover, several of its properties resemble those of a Majorana fermion which was predicted in 1937. Very recently we have also discovered that the first graphene layer to grow on the silicon terminated silicon carbide crystal face, which has long been considered to an insulator, is in fact an excellent semiconductor when it is properly annealed. It is found to have a band gap of 0.6 eV and a room temperature mobility that exceeds 5000 cm2/Vs, which is greater than that of silicon and exceeds all other 2D semiconductors by a factor of 20 or more (Nature, in press). These two breakthrough discoveries put epigraphene on the path to become an important new 2D electronic material.

1. Berger, C., et al., Ultrathin Epitaxial Graphite:  2D Electron Gas Properties and a Route toward Graphene-based Nanoelectronics. The Journal of Physical Chemistry B, 2004. 108(52): p. 19912

2. de Heer, W.A., Berger,C, First,P.N, Patterned thin film graphite devices and method for making same. US patent US7015142B2 (Provisional filed Jun. 12, 2003).

3. Prudkovskiy, V.S., et al., An epitaxial graphene platform for zero-energy edge state nanoelectronics. Nature Communications, 2022. 13(1): p. 7814.

Bio: Walt A. de Heer is a Georgia Tech Regents’ Professor of Physics. His pioneering epitaxial graphene program, initiated in 2001, was inspired by his discovery of the room temperature ballistic transport properties of carbon nanotubes in 1998 and focuses on developing a viable silicon carbide platform for graphene-based nanoelectronics, which is currently his main interest. He has published more than 400 papers on epigraphene, carbon nanotubes and metallic clusters. He has an h-index of 97, and he has received the Web of Science Group’s Highly Cited Researcher Award yearly from 2010-2019.

Host: Prof. Simon Sponberg

Title: : Information gathering as a guiding principle for animal (and robot) movement

Abstract: 

I study how organisms integrate sensory information from multiple modalities across time and space to make decisions in complex naturalistic environments. My end goal is twofold: to understand how brains process sensory information, and to generate new, bioinspired, algorithms for engineered systems that enable the kind of resilience characteristic of biology. In my talk I will describe recent work in my lab that leverages optogenetics in freely flying fruit flies to remotely activate their sense of smell. Using this approach, we discovered a novel behavior they localize odor sources in still air. We also show that flying flies are capable of estimating the presence and direction of ambient wind. To understand how they might achieve this my group developed new control-theoretic tools for empirically assessing the nonlinear observability of individual states—that is, what sensor combinations and movement motifs are required such that wind direction can be estimated. Finally, I will describe our preliminary efforts to design nonlinear observers for wind direction, and describe a framework for how this approach could lead to estimation strategies that are resilient to unanticipated measurement anomalies.

Bio: Floris van Breugel is an assistant professor at the University of Nevada, Reno in the Mechanical Engineering Department, with affiliations with the Integrative Neuroscience and Ecology and Evolution programs. Floris earned his BS in Biological Engineering at Cornell, where he worked with Hod Lipson on bio-inspired flapping machines. He earned his PhD in Control and Dynamical Systems at Caltech under Michael H Dickinson and Richard Murray, with support from Hertz and NSF fellowships. After continuing as a postdoc with Michael, he did a brief postdoc at the University of Washington with Jeff Riffell, Nathan Kutz, and Bing Brunton with support from a Moore/Sloan Data Science Fellowship. He started his lab at UNR in 2019. His research brings together control theory, neuroscience, behavior, and bio-inspired robotics.  

Title: Neutrinos, reactors & anomalies

Abstract: Abstract: Neutrinos were discovered using a nuclear reactor as a source and since then much of our knowledge about neutrinos comes from experiments using reactors. I will briefly touch on the history of the use of reactors as neutrino source and motivate why they still play an important role today and in the future. An overview of the physics of how neutrinos are generated in reactors and how we can compute neutrino fluxes will follow. The developments of the past decade will be reviewed in particular. 2021 may have seen the resolution of one major riddle regarding the neutrino yield from uranium-235 and I will comment on this. I also will present the current status of the sterile neutrino in electron neutrino disappearance  including recent gallium results. I will conclude with an outlook towards the future both for our understanding of the reactor neutrino flux and reactor neutrino measurements. I also will be touching on coherent elastic neutrino nucleus scattering at reactors.

Bio: Patrick Huber is a professor of physics and an affiliate professor in the nuclear engineering program and a member of the Virginia Tech faculty since 2008. Huber conducts research on neutrino physics. He has helped build an internationally recognized program in neutrino physics both in basic science and applications to global and national security. He has authored more than 170 publications and has built an impactful research program.

In 2010, Huber co-founded the Center for Neutrino Physics at Virginia Tech and since 2018 he is serving as its director.. He was a lead developer of the GLoBES software package which is the standard for computing the physics sensitivity of many large neutrino experiments. In 2011, he performed what is currently the most accurate calculation of the reactor antineutrino spectrum emitted by nuclear reactors.

He has been a member or leader of a large number of study and planning efforts in the neutrino community, including his current service on the Particle Physics Project Prioritization Panel (P5), setting the research and budget priorities for the field in the United States for the next decade.

He is the recipient of multiple awards, including the Fermilab Distinguished Scholar, the Breakthrough Prize in Fundamental Physics, Early Career Research Award of the U.S. Department of Energy Office of High Energy Physics and election as a Fellow of the American Physical Society.

He earned a master’s degree and Ph.D. from Technical University of Munich, Germany.

Title: From sea cells to sea shells

Abstract: At the microscopic scale, virtually everything moves. From diverse patterns of movement one can distinguish living from non-living matter, bacteria from eukaryotes, random from directed, purposeful movement. I will discuss our recent work on phenotyping the motility of diverse microeukaryotes from long-time trajectory statistics. These include microswimmers that orchestrate propulsion-generating appendages (cilia and flagella) for swimming through fluids, as well as organisms that glide mysteriously without the need to resort to any appendages at all. We derive species-agnostic measures of active motility from high-speed live imaging experiments. We show how to distinguish between distinct yet stereotyped states (or gaits) of activity, and demonstrate how environmental cues (e.g. physical confinement, light, chemicals) induce systems-level cellular signalling whose effect becomes measurable in terms of transition probabilities between states. Finally, we speculate on the implications of these findings for the evolution of cellular decision making in basal eukaryotes.

Bio: Kirsty Y. Wan is associate professor at the Living Systems Institute, University of Exeter, UK, where she heads an interdisciplinary group researching the biophysics of microscale navigation, with particular emphasis on the motility and coordination of cilia. She obtained her PhD in biological physics from the Department of Applied Mathematics and Theoretical Physics, University of Cambridge, where she also held a Thomas Nevile Junior Research Fellowship at Magdalene College (2014–2017). In 2020, she received an ERC Starting Grant to explore the origins of motility and cognition in diverse protists.

Title: Gravitational Wave Detectors during the 4th Observing Run of the Advanced Detector Era

Abstract: The era of gravitational wave astronomy has accelerated rapidly, from the first direct detection of gravitational waves in 2015 to our current observing run with candidate events detected several times per week.  The Laser Interferometer Gravitational wave Observatory (LIGO) is jointly operated by Caltech and MIT for the National Science Foundation, and is currently in an observing phase that began in May 2023, and will continue through 2024. I will discuss innovations that have enabled the unprecedented sensitivity of the Advanced LIGO detectors, plans for future upgrades, as well as the exciting plethora of gravitational wave candidates we have seen so far in our 4th observing run.

Bio: Dr. Jenne Driggers is the Detection Lead Scientist at the LIGO Hanford Observatory.  She completed her PhD at the LIGO Caltech 40m interferometer prototype in 2015, and was a postdoc at the LIGO Hanford Observatory before joining the observatory staff.

Host: Prof. Peter Yunker

Title: : Barbed end depolymerization and pointed end polymerization - turning treadmilling on its head

Abstract: 

Actin is an essential protein. For over two decades, intracellular actin filaments have been thought to elongate at their barbed ends and depolymerize from pointed ends. This process, referred to as “treadmilling” has formed the central bedrock of our understanding of actin dynamics. Recent results from our lab however suggest that the treadmilling dogma might not always hold true. Using a combination of in vitro multicolor single molecule and single filament reconstitution experiments, we have discovered two new activities that call for reevaluation of the treadmilling dogma. First, we discovered the first-ever pointed-end polymerase VopF that processively polymerizes filament pointed ends in cells and from purified proteins. Further, VopF accelerates polymerization in presence of profilin and is a mechanosensitive protein - its rate of polymerization increases under pN-range pulling forces. Second, we have recently discovered that twinfilin, a member of the cofilin family of proteins, induces depolymerization of filament barbed ends. Interestingly we find that the depolymerase twinfilin, polymerase formin and blocker CP form a multicomponent complex at the filament barbed end. Importantly, both of these processes persist in physiological conditions containing high concentrations of profilin-bound monomers – strongly indicating intracellular implications for these newly discovered activities. Taken together, our findings call for taking a fresh look at actin treadmilling and its implications in cellular actin dynamics.

Biography:
Dr. Shashank Shekhar is an assistant professor of physics and cell biology at Emory University. His research interests in biological self-assembly lie at the interface of physics, biology and biochemistry. He is the recipient of several awards including the Whitman Early Career Award at the Marine Biological Laboratory and the Grand advances in Biology Prize from the French Academy of Sciences. He received his PhD in experimental cell biophysics from University of Twente (The Netherlands). He earned his master’s in Nanoscience and Molecular Bioengineering from TU Delft (Netherlands) and TU Dresden (Germany) and undergraduate degree in Physics in India.

Title: Beyond the Images: Astrochemistry with the James Webb Space Telescope

Abstract: 

In late 2021, the James Webb Space Telescope (JWST) was launched into space on an Ariane 5 rocket from French Guiana. JWST has unprecedented sensitivity and angular resolution and is now the premier space-based facility for near- and mid-infrared (0.6-28.5 μm) astronomy. The 6.5-meter telescope is equipped with four state-of-the-art instruments which include imaging, spectroscopy, and coronagraphy modes. These instruments are already returning amazing spectra and images of distant galaxies, star-forming regions, and planets in and out of the solar system. JWST's spectroscopic capabilities have already provided details of the composition of star forming regions, evolved stars, and planetary atmospheres that have not been measured previously. The complementary nature of this observatory with other high resolution imaging facilities (e.g., ALMA) will help us further our understanding of molecular heritage throughout the stellar lifecycle. We are entering the next era of Astrochemistry with JWST as we start to disentangle the complex molecular processes in the solar system, throughout the galaxy, and beyond. This presentation will highlight the some of the first Astrochemistry results with JWST and the capabilities it has to offer for this field of study.

Bio:

Dr. Milam works in the Astrochemistry Laboratory at the NASA Goddard Space Flight Center. She is an expert in rotational spectroscopy, observations, and laboratory modeling of astrochemistry and molecular astrophysics of the interstellar medium, evolved stars, star formation regions, and comets. Her observational focus is on the compositional studies of primitive bodies, namely comets and interstellar objects, and uses ground- and space-based facilities to understand their connection to the formation and evolution of planetary systems. She also has a laboratory dedicated to simulate interstellar/cometary/planetary ices and detect trace species employing the same techniques used for remote observations to help constrain the chemical complexity of the ices, the amount of processing that occurs, and interpret past and present data from missions that observe ice features.  Dr. Milam has been working on the James Webb Space Telescope (JWST) as Deputy Project Scientist for Planetary Science since 2014. Under this role she has helped enable observations within our own solar system from Near-Earth Asteroids to the farthest reaches of the Kuiper belt and even the brightest objects in the infrared sky (e.g. Mars). She has also led the study team for solar system science for WFIRST. In 2021, she was honored with asteroid 40706 (1999 RO240) was renamed to 40706 Milam. She received the NASA Exceptional Scientific Achievement Medal in 2022 for her work on enabling Solar System Science with JWST.

Title: 101 Mistakes to Avoid Before Submitting a Paper

Abstract: There is a strong desire, often driven by real or perceived pressures, to publish research in a top tier journal like Science.  However, with a rejection rate above 93%, it is a difficult process.  Beyond this, the publication landscape has gotten more complex with pre-print servers, predatory journals, mega-publishers, etc.  In this talk, I will describe the publication process at Science, within the broader context of publishing good papers in any journal.  I will focus on steps you can take to simplify the process both prior to submission and during the review and revision process.

Bio:

Undergrad – Chemical Engineering at the University of Toronto (Canada)

PhD – Materials Science at Cambridge University (UK)

Post-docs @ Bristol (Physics) (UK) and MIT (Chemical Engineering) (US)

Started as an editor at Science in 2001

Host: Prof. Harold Kim

Title: : Direct Observation of Self-Assembled Water Chains and their Coil-to-Bridge Transitions in a Nanoscopic Meniscus 

Abstract: 

Structures and behaviors of water confined between two surfaces are important in bio/nano sciences and water-based nanotechnology. I report observations of self-assembled water chains and their transitions from a coil state to a bridge state in a nanoscopic water meniscus in air. Large sawtooth-like oscillatory forces were shown when the normal and friction forces were measured as a function of distance between a sharp probe and a flat oxidized silicon surfaces using a force-feedback force microscope called “cantilever-based optical interfacial force microscope” (COIFM). In the force-distance plot, each oscillation is comprised of a rising-shaped (ö)  curve in the upward portion and a sigmoidal-shaped (ò) curve in the downward portion as the tip-sample distance decreases. Further analysis of each upward portion with the freely joined chain (FJC) model reveals that each portion is developed from self-assembled water chains with lengths ranging from 14 to 42 chain units in the meniscus. The analysis of downward portions reveals that each portion is generated by a “coil-to-bridge” transition of self-assembled water chains, whose lengths are between 197 and 383 chain units. The observed coil-to-bridge transitions explain many mysterious properties of confined water at the nanometer scale (e.g. long condensation distances, long nucleation timescale, high surface tension, long-range biomolecular interactions, etc.), thus dramatically improving the understanding of a variety of water systems in nature [1].

1. Byung Il Kim, Self-Assembled Water Chains: A Scanning Probe Microscopy Approach (Springer Nature, 2023).

Title: Searching for a Gravitational Wave Background with Pulsar Timing Arrays

Abstract: 

Bio: Sarah Vigeland is a gravitational wave astrophysicist whose work focuses on detecting gravitational waves with pulsar timing arrays. She is a member of the NANOGrav Collaboration, and currently serves as chair of the Gravitational Wave Detection Working Group. She earned her Ph.D. from MIT in 2012, and did postdocs at the Jet Propulsion Laboratory and the University of Wisconsin-Milwaukee before joining the faculty at the University of Wisconsin-Milwaukee as an assistant professor in 2019.

Title: The Blob: Topologically Entangled Living Matter

Abstract: Tangled active filaments are ubiquitous in nature, from chromosomal DNA and cilia carpets to root networks and worm collectives. How activity and elasticity facilitate collective topological transformations in living tangled matter is not well understood. In this talk, I will share our discoveries on why aquatic worms braid, tangle, and knot with their neighbors to form extraordinary mechano-functional living blobs - the stuff of science fiction. I will discuss how these soft, squishy, and 3-D blobs rapidly morph their shape, crawl, float, climb, self-assemble, and disassemble topological tangles. Using both mathematical models and robotic analogs, I will discuss how these “living polymers” solve Gordian knot problems using clever biophysics mechanisms that open a path to new classes of active topologically tunable robotic swarms.

Bio: 

Saad Bhamla studies biomechanics across species to engineer knowledge and tools that inspire curiosity. Saad Bhamla is an assistant professor of biomolecular engineering at Georgia Tech. A self-proclaimed "tinkerer," his lab is a trove of discoveries and inventions that span biology, physics and engineering. His current projects include studying the hydrodynamics of insect urine, worm blob locomotion and ultra-low-cost devices for global health. His work has appeared in the New York Times, the Economist, CNN, Wired, NPR, the Wall Street Journal and more. Saad is a prolific inventor and his most notable inventions includes a 20-cent paper centrifuge, a 23-cent electroporator, and the 96-cent hearing aid. Saad's work is recognised by numerous awards including a NIH R35 Outstanding Investigator Award, NSF CAREER Award, CTL/BP Junior Faculty Teaching Excellence Award, and INDEX: Design to Improve Life Award. Saad is also a National Geographic Explorer and a TED speaker. Newsweek recognized Saad as 1 of 10 Innovators disrupting healthcare. Saad is a co-founder of Piezo Therapeutics. Outside of the lab, Saad loves to go hiking with his partner and two dogs (Ollie and Bella).

Title: Active structures and flows in living cells

Abstract: Flows in the fluidic interior of living cells can serve function, and by their structure shed light on how forces are exerted within the cell. Some of these flows can arise through novel collective instabilities of the cytoskeleton, that set of polymers, cross-linkers, and molecular motors that underlie much of the mechanics within and between cells. I'll discuss experiments, mathematical modeling and analysis, and simulations of two such cases. One is understanding the emergence of cell-spanning vortical flows in developing egg cells, while the other arises from studying the nature of force transduction in the dynamics of microtubule arrays inside of synthetic cells. Both show the importance of polymer density in determining dynamics and time-scales, and have required the development of new coarse-grained models and simulation methods.

Bio: Dr. Michael J. Shelley is an applied mathematician who works on the modeling and simulation of complex systems arising in physics and biology. This has included, of late, modeling the dynamics of complex and active fluids, and examining transport and self-organization processes in cellular biophysics. He is co-founder and co-director of the Courant Institute's Applied Mathematics Lab at New York University, and is the Director of the Center for Computational Biology at the Flatiron Institute. He is a Fellow of the American Physical Society, the Society for Industrial and Applied Mathematics, and the American Academy of Arts and Sciences, and is a member of the National Academy of Sciences.

Title: Open quantum systems in cosmology

Abstract: The open questions in cosmology have been open for decades: Why is the present-day universe undergoing accelerated expansion? What is the particle physics behind the origin of structure in the universe? What is the dark matter? All of these questions must be answered in the framework of a quantum theory, and at least two also require quantum gravity. I will discuss why open quantum systems, where an unobserved environment affects the evolution of the observed system, are starting to play a more prominent role in cosmology and how they help to generate new ideas for long-standing puzzles.

Title: Error Mitigation and Suppression in Superconducting Quantum Processors

Abstract: In principle, quantum computers have the potential to be able to solve problems that are intractable with classical computers. However, all currently existing quantum platforms suffer from errors; typical state of the art error rates are approximately one error per thousand operations. The central problem in building and operating these devices successfully is how we deal with these errors. Using superconducting quantum processors as an example, I will discuss some sources of errors, including decoherence, crosstalk, and control noise. With these in mind, I will then discuss at a high level three main strategies for handling these errors: error suppression, error mitigation, and error correction.

Bio: Dr. Oliver Dial was named an IBM Fellow in 2021 for his contributions to quantum computing hardware. He is IBM Quantum’s CTO, ensuring IBM’s quantum hardware and software together deliver an outstanding experience. Oliver received his PhD from MIT in 2007 for research in two-dimensional electron and hole systems. He then entered the field of quantum computing as a post-doc at Harvard, demonstrating the first two-qubit gate between semiconductor singlet-triplet qubits and performing pioneering charge noise spectroscopy in these systems. He joined IBM as a research scientist in 2012.

Committee members:
Dr. James (JC) Gumbart, School of Physics, Georgia Institute of Technology (advisor)
Dr. Simon Sponberg, School of Physics, Georgia Institute of Technology
Dr. Peter Yunker, School of Physics, Georgia Institute of Technology
Dr. Ingeborg Schmidt-Krey, School of Chemistry & Biochemistry, Georgia Institute of Technology
Dr. Lynn Kamerlin, School of Chemistry & Biochemistry, Georgia Institute of Technology

Abstract: “This dissertation explores the evolution and development of proteins, specifically membrane-embedded proteins in microorganisms, including viruses and bacteria, using computational methodologies like Molecular Dynamics (MD) simulations and machine learning techniques.

We first study outer-membrane proteins (OMPs) in Gram-negative bacteria, specifically the Escherichia coli protein OmpX. Through simulation of its engineered variants, we find a link between β-barrel size, shape, and the presence of inward-facing glycines. we find that the fraction of glycines in β-barrels decreases as the strand number increases, suggesting an evolutionary role in the addition or removal of glycine in OMP sequences.

Next, our investigation shifts to the Spike protein in SARS-CoV and SARS-CoV-2 viruses. Despite differences in their receptor-binding domains, the two proteins bind to the human ACE2 receptor in similar ways. Using MD simulations, machine learning, and free-energy perturbation calculations, we quantify these subtle mutations and demonstrate how evolutionary changes directly influence binding affinity.

Lastly, we study the glycosylation profiles of virus variants and their impact on the glycan shield of the Spike protein. Our findings reveal that the Spike protein in the Omicron variant is less enveloped by glycans, affecting the accessible area in specific residues.

This work sheds light on the evolution of membrane proteins, their structure, interactions, and glycan shields, offering valuable insights into protein evolution.”

Committee:      Dr. Roman Grigoriev, Department of Physics, Georgia Institute of Technology (advisor)
                          Dr. Michael Schatz, Department of Physics, Georgia Institute of Technology
                          Dr. Kurt Wiesenfeld, Department of Physics, Georgia Institute of Technology
                          Dr. Elisabetta Matsumoto, Department of Physics, Georgia Institute of Technology
                          Dr. Alberto Fernandez-Nieves, Department of Physics, University of Barcelona

Summary:

The Sparse Physics-Informed Discovery of Empirical Relations (SPIDER) algorithm is a technique for data-driven discovery of partial differential equations (PDEs). SPIDER combines knowledge of symmetries, physical constraints like locality, the weak formulation of differential equations, and sparse regression to find new physical descriptions of data with spatiotemporal variation. SPIDER is a valuable tool in synthesizing scientific knowledge as demonstrated by its applications.

A novel feature of this algorithm is to not only learn physics in a symmetry-consistent way, but to learn only relations in irreducible representations. That is, relations are broken down into their indivisible parts, so that each PDE is learned truly independently. This prevents implicit bias and unknowingly using evidence from one relation for an independent one. A library of nonlinear functions is constructed for each irreducible representation of interest, and sparse linear combinations of these library terms are sought.

The weak formulation of differential equations is used: library terms are sampled not at individual points but integrated over spacetime domains with flexible weight functions. Integration by parts sidesteps numerical differentiation in many situations and increases robustness to noise by orders of magnitude. Clever weight functions can remove discontinuities and even entirely remove unobserved fields from analysis. Once these library terms have been sampled, sparse regression algorithms can find relations ranging from dominant balances to multi-scale quantitatively accurate PDEs.

Applications to numerical 3D fluid turbulence and 2D active nematic turbulence are presented. It is demonstrated that SPIDER can recover complete mathematical models of both systems and consistent redundancies across disjoint irreducible representations. In every representation analyzed, at least one relation is found. The active nematic system is of particular interest, as a new effective 2D description of the system is identified by SPIDER. While this system of equations holds only in regions of saturated microtubule density, it offers valuable physical insight.

Committee: 

Dr. Colin Parker, School of Physics, Georgia Institute of Technology (advisor)
Dr. Michael Chapman, School of Physics, Georgia Institute of Technology
Dr. Brian Kennedy, School of Physics, Georgia Institute of Technology
Dr. Martin Mourigal, School of Physics, Georgia Institute of Technology
Dr. Joshua Kretchmer, School of Chemistry and Biochemistry, Georgia Institute of Technology

Abstract:

Real world material systems often have properties with roots in quantum mechanics which we are interested in. Studying such systems by classical models is often unsuitable, being either ineffective or inefficient. The general approach is through quantum simulations, in which laser cooled and trapped atoms are used as simulators. This thesis presents our study of ultracold quantum gases of Li-6, signifying our progress in building a quantum simulator. At first, we demonstrate the achievement of molecular BECs of Li-6 in its lowest and second lowest hyperfine state pairs by an all-optical method. We employ mostly standard techniques, but also introduce several unique features in our hardware system. Then, by preparing a degenerate Fermi gas of Li-6 in a mixture of its second lowest two hyperfine states and measuring its spin susceptibility in the BEC-BCS crossover, we study the “pseudogap” effects and compare it to the high-Tc cuprates. We develop a novel radiofrequency method to map the mixture to an RF-dressed basis. Imbalances are created between thermally equilibrium RF-dressed states, from which the spin susceptibilities are extracted over the interaction strength-temperature phase diagram. The results of such measurements for gases in the strongly interacting regions are compared to a mean-field model, to the ideal Fermi gas model, and to experimental results from several other publications. Lastly, we implement a 1D optical lattice. We tune the single particle dispersion relation using a shaken lattice by Floquet engineering. The driving signal is modulated through an IQ modulator fed to two AOMs. By loading a molecular BEC of Li-6 pairs into the shaking lattice, we have achieved coupling between the first two energy bands resulting in a double-well dispersion. The major result of our observations is that the atomic cloud under the inverted dispersion bifurcats into two soliton-like peaks in the momentum space. While in the position space, a density corrugation is formed in the atom cloud, which is caused by the two bifurcated wave peaks with opposing momentum beginning to separate. We have not yet fully understood the mechanism behind this phenomenon. For now, we model the result semi-classically by the Gross-Pitaevskii equation. The numerical simulations match reasonably well with the experimental results. 

Committee:
Dr. Gongjie Li, School of Physics, Georgia Institute of Technology
Dr. Tamara Bogdanovic, School of Physics, Georgia Institute of Technology
Dr. Predrag Cvitanovic, School of Physics, Georgia Institute of Technology
Dr. Chris Reinhard, School of Earth & Atmospheric Sciences, Georgia Institute of Technology
Dr. Smadar Naoz, Department of Physics and Astronomy, UCLA

Abstract
This work focuses on the gravitational interactions of astrophysical systems. In particular, we focus on the triple system dynamics, including mildly hierarchical three body secular dynamics, as well as precession induced resonances of binaries under the perturbation of a third companion. We apply our theoretical investigations of these physical processes to wide-orbit planetary systems and black hole binaries embedded in AGN disks.

More specifically, we consider the secular dynamics of a test particle in a mildly-hierarchical configuration. We find the limit within which the secular approximation is reliable, present resonances and chaotic regions using surface of sections, and characterize regions of phase space that allow large eccentricity and inclination variations. Finally, we apply the secular results to the outer solar system. We focus on the distribution of extreme trans-neptunian objects (eTNOs) under the perturbation of a possible outer planet (Planet-9), and find that in addition to a low inclination Planet-9, a polar or a counter-orbiting one could also produce pericenter clustering of eTNOs, while the polar one leads to a wider spread of eTNO inclinations.

Beyond mildly hierarchical triple dynamics, we also propose a novel pathway through which compact binaries could merge due to eccentricity excitation, including in a near coplanar configuration. Mechanisms have been proposed to enhance the merger rate of stellar mass black hole binaries, such as the Von Zeipel-Lidov-Kozai mechanism (vZLK). However, high inclinations are required in order to greatly excite the eccentricity and to reduce the merger time through vZLK. Specifically, a compact binary migrating in an AGN disk could be captured in a precession-induced resonance, when the apsidial and nodal precession rates of the binary are commensurable to the orbital period around the supermassive black hole. We find 8 such resonances upto quardupole order of the Hamiltonian.  We show that if a binary is captured in these resonances and is migrating towards the companion, it can experience large eccentricity and inclination variations. Eccentricity is excited when the binary sweeps through the resonance which happens only when it migrates on a timescale 10-100 times the libration timescale of the resonance. Libration timescale decreases as the mass of the disk increases. The eccentricity excitation of the binary can reduce the merger timescale by a factor up to $10^{3−5}$.

Committee:
Dr. Roman Grigoriev, Department of Physics, Georgia Institute of Technology (advisor)
Dr. Michael Schatz, Department of Physics, Georgia Institute of Technology
Dr. Kurt Wiesenfeld, Department of Physics, Georgia Institute of Technology
Dr. Predrag Cvitanović, Department of Physics, Georgia Institute of Technology
Dr. Luca Dieci, Department of Mathematics, Georgia Institute of Technology

Abstract
Chaos is an intrinsic property of many real world systems, impacting a number of today's open research questions. While many chaotic systems have known governing equations and are deterministically ``solved," we still lack a comprehensive framework for predicting, controlling, and simply making sense of such systems. And while recent advances in technology allow us to explore these systems through direct numerical simulation better than ever before, the need for an insightful theoretical framework is still very much alive. 

Such a framework exists in a subset of chaotic systems, known as Axiom A chaotic systems and, as a result, Axiom A systems are understood quite well. However, the requirements for a system to be Axiom A are quite strict, and the overlap between systems that are Axiom A and those that are physically significant is quite small.

A very important concept in Axiom A systems is the notion of shadowing, which allows the chaotic dynamics to be decomposed piecewise-in-time in terms of much easier to analyze solutions known as periodic orbits. Periodic orbits are solutions to the governing equations that, unlike chaos, repeat in time. Their compactness make periodic orbits very simple objects to manipulate, both numerically and theoretically. A decomposition in terms of periodic orbits results in a predictive theory of Axiom A systems, both deterministically and statistically.

In this talk, I will discuss how to generalize aspects of this decomposition to a broader class of (non Axiom A) chaotic systems, specifically, fluid turbulence. Although recent studies suggest that Exact Coherent Structures (ECS)---e.g., repeating solutions to the Navier-Stokes equation---are descriptive of turbulence, it is an open question whether they are to turbulence what periodic orbits are to Axiom A chaos. I will present evidence of ECS being shadowed by turbulence in various fluid geometries and, additionally, present preliminary work suggesting a statistical picture of turbulence in terms of ECS may also be feasible. "

Title: Entropy, molecular motors, and non-thermal equilibrium statistical physics

Abstract: The transport of molecular cargos in neuronal cells is analyzed in the context of new developments in statistical physics. Our development of very bright optical probes enabled the long-term single tracking of molecular cargos in live neurons for tens of minutes. The number of dynein motors transporting a cargo was found to switch stochastically from one to up to five motors during the long-range transport in neurons. We are able to resolve individual molecular steps, and formulated a new, quantitative chemo-mechanical model where two ATP molecules are hydrolyzed sequentially. Our model is consistent with extensive structural, single-molecule and biochemical measurements.

The observed fluctuations in movement can be described by a steady-state non-thermal equilibrium effective temperature. The Fluctuation Theorem, first proved in 1993 and applicable in any non-thermal equilibrium processes, is shown to yield a minimum “uncertainty principle” limit, where the product of heat entropy and the statistical precision of any physical operation is greater than or equal to 2kBT. In the context of intercellular molecular transport, we show that a smaller variance in the movement of the cargo vesicle demands a greater expenditure of energy.

Committee:
Dr. Chandra Raman, School of Physics, Georgia Institute of Technology (advisor)
Dr. Colin Parker, School of Physics, Georgia Institute of Technology
Dr. Carlos Sa de Melo, School of Physics, Georgia Institute of Technology
Dr. Martin Mourigal, School of Physics, Georgia Institute of Technology
Dr. Ronghua Pan, School of Mathematics, Georgia Institute of Technology

Abstract: 
Relaxation or thermalization of isolated or driven quantum systems has drawn considerable research interest, and defect formation is known to be closely related to the progress towards equilibrium or steady states. In our work, we use quasi-1D spinor Bose-Einstein condensates (BECs) as platforms to tackle such non-equilibrium problems. The spinful superfluids feature for their rich internal degrees of freedom and give rise to novel defects such as vector solitons. We report on our studies of two essential ingredients of non-equilibrium dynamics in spinor BECs, namely magnetic solitons and spin waves. Using a spin-dependent phase imprinting technique, we generate magnetic solitons in an antiferromagnetic spin-1 BEC, where the solitons manifest themselves as a localized spin excitation propagating upon a balanced two-component condensate[1]. The study is then extended to three-component solitons by harnessing the underlying SO(3) symmetry of the spin-1 manifold[2]. Moreover, we theoretically explore magnetic solitons in ferromagnetic spin-1 BECs, where the solitons behave as a local spin-flip propagating on top of a spin-polarized background[3]. Most recently, we investigate resonance phenomena in a driven spinor BEC. By driving the quadratic Zeeman shift periodically, we observe the spin waves generated from the parametric amplification of the spin-mixing dynamics.

[1] Phys. Rev. Lett. 125, 030402

[2] Phys. Rev. Research 3, L012003

[3] Phys. Rev. A 105, 013313