Physics seminars

A high-dimensional nonlinear recurrent neural network is driven by periodic, incoherent inputs while its synapses undergo Hebbian-like plasticity. Depending on drive and plasticity strengths, the network can retain autonomous limit-cycle activity after both the inputs and learning are removed. Dynamical mean-field theory and finite-size simulations characterize the resulting rhythmic memories and transitions between chaotic, fixed-point and oscillatory regimes. Memory robustness depends on the interval between removing the input and stopping plasticity. These results suggest a mechanism by which neural circuits learn and maintain biological rhythms.

Adriana Milic examines how the ATLAS liquid-argon calorimeter supports rapid event selection. After introducing its readout architecture, she explains the Phase-I change from analogue triggering to finely segmented digital Super Cells. Increased granularity, precision and dynamic range enable better background rejection during high-pile-up Run 3 collisions. Finer segmentation also changes signal-to-noise behaviour and the efficiency for low-energy deposits, creating distinct challenges in heavy-ion data taking. The seminar then considers Phase-II plans for greater bandwidth and full-calorimeter information, enabling more sophisticated selection under the conditions expected at the High-Luminosity LHC.

Intermediate-band solar cells seek to absorb photons below the host band gap and increase current without sacrificing voltage. This talk examines submonolayer CdTe quantum dots embedded in ZnCdSe matched to InP, avoiding a harmful wetting layer and permitting hundreds of absorbing layers. Recent growth results show deeper photoluminescence associated with larger dots and improved intermediate-band placement. A complementary inverse-design study optimizes ZnCdSe/ZnCdMgSe distributed Bragg reflectors to recycle photons over 1–1.8 micrometres and incidence angles of 0–70 degrees. Total absorption guides optimization, with designs showing broad reflectivity and tolerance to fabrication errors.

Runaway electrons can severely damage plasma-facing components in current and future tokamaks. This webinar presents a research roadmap connecting runaway-electron models with plasma–surface interactions and material-damage calculations. It examines the physics, experiments, model integration and validation needed to predict electron loads and damage at reactor walls. The speakers assess current capabilities, gaps in modeling chains, and challenges for ITER and subsequent fusion devices.

Complementary nanoscale methods can extract different structural and material information from the same specimen, but combining them demands precise positioning and access. Alexandra Glück examines flexible multi-axis sample manipulation across electron microscopy, spectroscopy, diffraction, probing, nanoindentation and tomography. SmarAct’s customizable SEM platform illustrates approaches to alignment, measurement geometry and transitions between techniques, including in-situ experiments. The emphasis is on how adaptable manipulation enables complementary measurements to build a fuller account of a specimen’s structure and properties. An interactive discussion follows.

The talk explores a quantitative connection between Huygens’s legacies in wave optics and classical mechanics. Optical polarization, coherence and entanglement are related to mechanical quantities including centre of mass and moment of inertia. Distributions of classical point masses provide a representation of nonseparability in optical fields, and the correspondence extends to quantum states of two qubits. These mappings offer an intuitive way to examine entanglement and the shared mathematical structure of mechanics, classical optics and quantum physics.

Gang Chen delivers MIT.nano's annual Dresselhaus Lecture, drawing on research that spans electron and phonon transport, thermoelectric energy conversion, microelectronic thermal management, desalination and data-center cooling.

Water’s rapidly changing hydrogen-bond network links molecular interactions to its unusual bulk properties. The talk introduces correlated vibrational spectroscopy (CVS), which combines higher-order optical measurements, symmetry selection and angular polarimetry to isolate signals from interacting molecules and directly examine low-frequency hydrogen-bond stretching. CVS measurements reveal electronic charge transfer and nuclear quantum effects in water and acidic or basic solutions. Hydroxide donates roughly 8% more negative charge to the network than water, while protons reduce transfer by less than 4%. Nuclear quantum effects weaken hydrogen bonds in pure water by about 10% and change charge transfer in acidic, but not basic, solutions. In acids, charge is accepted locally by a proton and reduced by its delocalization. In bases, donation extends across several hydration shells, beyond the region affected by proton delocalization. The presentation explains how these measurements probe intermolecular correlations and concludes with further applications of CVS.

Ball lightning has resisted explanation for nearly two centuries. Correlating eyewitness reports with lightning-location measurements now provides evidence beyond isolated observations. The talk examines the strokes associated with ball-lightning formation, develops a hypothesis for its production, and evaluates competing classes of theory against observed properties and the proposed creation mechanism.

Coherent neutrino–nucleus scattering accesses reactor antineutrinos below the inverse-beta-decay threshold. Reconstructing their spectrum requires unfolding nuclear recoils. A method adapted from dark-matter searches avoids hand-tuned regularization and matches standard techniques on simulated cryogenic germanium data. A relativistic multiplayer outreach game may also be discussed.

This seminar connects carbonization conditions with the structure and function of carbon made from discarded plastics and food-derived sugars. Commodity plastics are carbonized under autogenic pressure in sealed quartz capillaries; sugars undergo neutral and alkaline hydrothermal processing in water and ionic liquids. Time-resolved WAXS, SAXS and Raman measurements, supported by ex situ XPS, track organic networks as they become carbonaceous solids. SAXS identifies emerging porosity and density variation, WAXS follows short-range aromatic stacking, and Raman D and G bands measure evolving sp2 domains and defects. XPS distinguishes oxygen-rich hydrothermal chars from plastic-derived carbons with lower oxygen-to-carbon ratios and stronger graphitization signatures. The combined observations relate precursor chemistry to intramolecular rearrangement, intermolecular crosslinking, pore formation and aromatic ordering under pressure.

Ruchi Mishra compares magnetized accretion onto charged black holes and horizonless compact objects using ongoing three-dimensional general-relativistic magnetohydrodynamic simulations. In a Reissner–Nordström spacetime whose charge exceeds its mass, a naked singularity replaces the event horizon, with a repulsive region, a zero-gravity radius, and a different structure of circular orbits. Earlier equilibrium calculations found toroidal rotating-fluid configurations around such singularities. Building on that work, the simulations examine how charge changes the accumulation of matter, transport of angular momentum, and organization of magnetic fields.