Publications

    The Black Hole Explorer: using the photon ring to visualize spacetime around the black hole
    Peter Galison, Alexandru Lupsasca, and Michael Johnson. In Preparation. “The Black Hole Explorer: using the photon ring to visualize spacetime around the black hole .” In Space Telescopes and Instrumentation 2024: Optical, Infrared, and Millimeter Wave. Yokohama, Japan. Read on SPIE.orgAbstract

    The Black Hole Explorer (BHEX), is an orbiting, multi-band, millimeter radio-telescope, in hybrid combination with millimeter terrestrial radio-telescopes, designed to discover and measure the thin photon ring around the supermassive black holes M87* and Sgr A*. In order to guide the mission design for the BHEX instruments, this paper explores various aspects of the photon ring, like the spin-induced changes to its shape, or the intricate flow of light around a spinning black hole, by tracking, through visual simulations, photons as they course along geodesics. Ultimately, the aim of these visualizations is to advance the foundational aims of the EHE instrument, and through this experiment to articulate spacetime geometry via the photon ring.

    Manja Klemenčič, Rexford Akrong, Bismark Amefianu Kudoafor, Sebastian Berger, Bianca Borges dos Santos, Mauro Conti, Martina Darmanin, Leonel Freeman, Igor Gonçalves, Jakub Grodecki, Martin Hammerbauer, Amanda Harumy, Kristel Jakobson, Abdul Karim Ibrahim, N’Gouran Kouame Tani Climbie Desire, Peter Kwasi Kodjie, Giuseppe Lipari, Antonio Lopez, Cynthia Mahop, Elorm Mawuli-Kwawu, Ricardo Miranda, Folabit Lena Novel, Estefania Peñuelas, Georgia Potton, Everton Rattray, Musarrat Maisha Reza, Carmen Romero, Amílcar Sanatan, Ankit Tripathi, Matteo Vespa, Christina Williams, Abdul Mufeez Shaheed, Awurama Kyei Baffour, and Andrews Kwasi Boahen. In Preparation. “Student politics revisited. Insights from a global comparative research project.”.
    Martina Darmanin, Jakub Grodecki, Martin Hammerbauer, Kristel Jakobson, and Matteo Vespa. In Preparation. “Student Politics in Europe”.
    Sebastian Berger, Bianca Borges dos Santos, Giuseppe Lipari, Folabit Lena Novel, Georgia Potton, Carmen Romero, Amílcar Sanatan, and Ankit Tripathi. In Preparation. “Global Student Forum.” In Student Politics Globally.
    E. N. Glezer. Submitted. “Method and apparatus providing 2-D/3-D optical information storage and retrieval in transparent materials”.Abstract
    Sub-micron-scale, micron-scale and greater than micron-scale, crack-free and regularly-shaped structures of high-contrast refractive index are provided in transparent storage media by controllably focusing ultrashort laser pulses in the bulk of virtually any transparent medium respectively during operation in a "low energy," a "high energy", and a "third" operating regime. In any operating regime, the crack-free and regularly-shaped structures of high-contrast refractive index may be controllably patterned in 2-D or 3-D so as to permanently store both digital and non-digital information in the bulk of the transparent storage medium. For digital-type information, greater than one (1) Terabit, and up to one hundred (100) Terabit, digital information storage capacity in a CD-ROM sized disc is provided. Virtually any non-digital information may be permanently stored therewithin, such as corporate logos, alphanumeric characters, security codes, and artistic images, or diffraction gratings, diffractive optical elements or other optical structures. Information permanently stored in 2-D or 3-D in the bulk of any transparent medium is read by the unaided eye, and by optical microscopy (scattered and transmitted light modes), phase contrast microscopy, laser DIC microscopy and confocal microscopy in dependance on the type of the information and on the operating regime. Information may be written or read in series or in parallel.
    Angelo Ricarte, Charles Gammie, Ramesh Narayan, and Ben S. Prather. Submitted. “Probing Plasma Physics with Spectral Index Maps of Accreting Black Holes on Event Horizon Scales .” Monthly Notices of the Royal Astronomical Society. Publisher's VersionAbstract

    The Event Horizon Telescope (EHT) collaboration has produced the first resolved images of M87*, the supermassive black hole at the centre of the elliptical galaxy M87. As both technology and analysis pipelines improve, it will soon become possible to produce spectral index maps of black hole accretion flows on event horizon scales. In this work, we predict spectral index maps of both M87* and Sgr A* by applying the general relativistic radiative transfer (GRRT) code {\sc ipole} to a suite of general relativistic magnetohydrodynamic (GRMHD) simulations. We analytically explore how the spectral index increases with increasing magnetic field strength, electron temperature, and optical depth. Consequently, spectral index maps grow more negative with increasing radius in almost all models, since all of these quantities tend to be maximized near the event horizon. Additionally, photon ring geodesics exhibit more positive spectral indices, since they sample the innermost regions of the accretion flow with the most extreme plasma conditions. Spectral index maps are sensitive to highly uncertain plasma heating prescriptions (the electron temperature and distribution function). However, if our understanding of these aspects of plasma physics can be tightened, even the spatially unresolved spectral index around 230 GHz can be used to discriminate between models. In particular, Standard and Normal Evolution (SANE) flows tend to exhibit more negative spectral indices than Magnetically Arrested Disk (MAD) flows due to differences in the characteristic magnetic field strength and temperature of emitting plasma.

    Simon Batzner, Tess E. Smidt, Lixin Sun, Jonathan Mailoa, Mordechai Kornbluth, Nicola Molinari, and Boris Kozinsky. Submitted. “SE(3)-Equivariant Graph Neural Networks for Data-Efficienct and Accurate Interatomic Potentials”. PreprintAbstract
    This work presents Neural Equivariant Interatomic Potentials (NequIP), a SE(3)-equivariant neural network approach for learning interatomic potentials from ab-initio calculations for molecular dynamics simulations. While most contemporary symmetry-aware models use invariant convolutions and only act on scalars, NequIP employs SE(3)-equivariant convolutions for interactions of geometric tensors, resulting in a more information-rich and faithful representation of atomic environments. The method achieves state-of-the-art accuracy on a challenging set of diverse molecules and materials while exhibiting remarkable data efficiency. NequIP outperforms existing models with up to three orders of magnitude fewer training data, challenging the widely held belief that deep neural networks require massive training sets. The high data efficiency of the method allows for the construction of accurate potentials using high-order quantum chemical level of theory as reference and enables high-fidelity molecular dynamics simulations over long time scales.
    Yu Xie, Jonathan Vandermause, Lixin Sun, Andrea Cepellotti, and Boris Kozinsky. Submitted. “Fast Bayesian Force Fields from Active Learning: Study of Inter-Dimensional Transformation of Stanene”. Publisher's VersionAbstract
    We present a way to dramatically accelerate Gaussian process models for interatomic force fields based on many-body kernels by mapping both forces and uncertainties onto functions of low-dimensional features. This allows for automated active learning of models combining near-quantum accuracy, built-in uncertainty, and constant cost of evaluation that is comparable to classical analytical models, capable of simulating millions of atoms. Using this approach, we perform large scale molecular dynamics simulations of the stability of the stanene monolayer. We discover an unusual phase transformation mechanism of 2D stanene, where ripples lead to nucleation of bilayer defects, densification into a disordered multilayer structure, followed by formation of bulk liquid at high temperature or nucleation and growth of the 3D bcc crystal at low temperature. The presented method opens possibilities for rapid development of fast accurate uncertainty-aware models for simulating long-time large-scale dynamics of complex materials.
    Matthew Cavorsi, Beatrice Capelli, Lorenzo Sabattini, and Stephanie Gil. Submitted. “Multi-Robot Adversarial Resilience using Control Barrier Functions”.Abstract

    In this paper we present a control barrier function-based (CBF) resilience controller that provides resilience in a multi-robot network to adversaries. Previous approaches provide resilience by virtue of specific linear combinations of multiple control constraints. These combinations can be difficult to find and are sensitive to the addition of new constraints. Unlike previous approaches, the proposed CBF provides network resilience and is easily amenable to multiple other control constraints, such as collision and obstacle avoidance. The inclusion of such constraints is essential in order to implement a resilience controller on realistic robot platforms. We demonstrate the iability of the CBF-based resilience controller on real robotic systems through case studies on a multi-robot flocking problem in cluttered environments with the presence of adversarial robots.

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