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COMAP Early Science. VI. A First Look at the COMAP Galactic Plane Survey
No full textWe present early results from the CO Mapping Array Project (COMAP) Galactic Plane Survey conducted between 2019 June and 2021 April, spanning 20° ℓ b∣ ii regions and supernova remnants (SNRs). Using low- and high-frequency surveys to constrain free–free and thermal dust emission contributions, we find evidence of excess flux density at 30 GHz in six regions, which we interpret as anomalous microwave emission. Furthermore we model ultracompact H ii contributions using data from the 5 GHz CORNISH catalog and reject these as the cause of the 30 GHz excess. Six known SNRs are detected at 30 GHz, and we measure spectral indices consistent with the literature or show evidence of steepening. The flux density of the SNR W44 at 30 GHz is consistent with a power-law extrapolation from lower frequencies with no indication of spectral steepening in contrast with recent results from the Sardinia Radio Telescope. We also extract five hydrogen radio recombination lines (RRLs) to map the warm ionized gas, which can be used to estimate electron temperatures or to constrain continuum free–free emission. The full COMAP Galactic Plane Survey, to be released in 2023/2024, will span ℓ ∼ 20°–220° and will be the first large-scale radio continuum and RRL survey at 30 GHz with 4.′5 resolution
Modeling and performance analysis of the LUVOIR coronagraph instrument
No full textFuture space missions such as the Large UV/Optical/Infrared Surveyor (LUVOIR) and the Habitable Exoplanet Observatory, when equipped with coronagraphs with active wavefront control to suppress starlight, will allow the discovery and characterization of habitable exoplanets. The Extreme Coronagraph for Living Planetary Systems (ECLIPS) is the coronagraph instrument on the LUVOIR Surveyor mission concept, an 8- to 15-m segmented telescope. ECLIPS is split into three channels, namely, UV (200 to 400 nm), optical (400 to 850 nm), and near IR (850 nm to 2 μm), with each channel equipped with two deformable mirrors for wavefront control, a suite of coronagraph masks, a low-order/out-of-band wavefront sensor, and separate science imagers and spectrographs. The apodized pupil Lyot coronagraph and the vector vortex coronagraph are the baselined mask technologies for ECLIPS to enable the required contrast for observations in the habitable zones of nearby stars for LUVOIR-A (15-m telescope) and LUVOIR-B (8-m telescope), respectively. Their performance depends on active wavefront sensing and control, as well as metrology subsystems to compensate for aberrations induced by segment errors (e.g., piston and tip/tilt), secondary mirror misalignment, and global low-order wavefront errors. Here, we present the latest results of the simulation of these effects for the LUVOIR coronagraph instrument and discuss the achieved contrast for exoplanet detection and characterization after closed-loop wavefront estimation and control algorithms have been applied. Finally, we show simulated observations using high-fidelity spatial and spectral input models of complete planetary systems generated with the Haystacks code framework
Boronated Cyanometallates
No full textFourteen boronated cyanometallates ([M(CN-BR₃)₆]^(3/4/5–) (M = Cr, Mn, Fe, Ru, Os, R = BPh₃, B(2,4,6,-F₃C₆H₂)₃, B(C₆F5)₃) have been characterized by X-ray crystallography and spectroscopy [UV-vis-NIR, NMR, IR, spectroelectrochemistry, and magnetic circular dichroism (MCD)]; CASSCF+NEVPT2 methods were employed in calculations of electronic structures. For (t_(2g))⁵ electronic configurations, the lowest energy ligand-to-metal charge transfer (LMCT) absorptions and MCD C terms in the spectra of boronated species have been assigned to transitions from cyanide σ+π + B-C borane σ orbitals. CASSCF+NEVPT2 calculations including t1u and t2u orbitals reproduced t_(1u)/t_(2u) → t_(2g) excitation energies. All ([M(CN-BR3)6]3/4− complexes exhibited highly electrochemically reversible redox couples. Notably, the formal potentials of all five [M(CN-B(C₆F₅)₃)₆]³⁻ anions scale with LMCT energies; and Mn(I) and Cr(II) compounds, (K(18-crown-6))₅[Mn(CN-B(C6F₅)₃)₆] and (TBA)₄[Cr(CN-B(C₆F₅)₃)₆], are surprisingly stable. Continuous wave and pulsed electron paramagnetic resonance (hyperfine sublevel correlation) spectra were collected for all Cr(III) complexes; as expected, ¹⁴N hyperfine splittings are greater for (TBA)₃[Cr(NC-BPh₃)₆] than for (TBA)₃[Cr(CN-BPh₃)₆]. Using (TBA)₄[Fe(CN-B(C₆F₅)₃)₆] and (TBA)₃[Fe(CN)₆], a model flow battery was constructed and found to have an 80% energy efficiency
ACHORD: Communication-Aware Multi-Robot Coordination With Intermittent Connectivity
No full textCommunication is an important capability for multi-robot exploration because (1) inter-robot communication (comms) improves coverage efficiency and (2) robot-to-base comms improves situational awareness. Exploring comms-restricted (e.g., subterranean) environments requires a multi-robot system to tolerate and anticipate intermittent connectivity, and to carefully consider comms requirements, otherwise mission-critical data may be lost. In this paper, we describe and analyze ACHORD (Autonomous & Collaborative High-Bandwidth Operations with Radio Droppables), a multi-layer networking solution which tightly co-designs the network architecture and high-level decision-making for improved comms. ACHORD provides bandwidth prioritization and timely and reliable data transfer despite intermittent connectivity. Furthermore, it exposes low-layer networking metrics to the application layer to enable robots to autonomously monitor, map, and extend the network via droppable radios, as well as restore connectivity to improve collaborative exploration. We evaluate our solution with respect to the comms performance in several challenging underground environments including the DARPA SubT Finals competition environment. Our findings support the use of data stratification and flow control to improve bandwidth-usage
A Barrier-Based Scenario Approach to Verifying Safety-Critical Systems
No full textWe detail an approach to safety-critical verification using barrier functions. Our method requires limited system data to verify a system's ability to keep positive a candidate barrier function h at discrete-time intervals over its trajectories. Specifically, our method first randomly samples initial conditions and parameters for a controlled, continuous-time system and records the state trajectory at discrete intervals. Then, we evaluate these states under a candidate barrier function h to determine the constraints for a randomized linear program. The solution to this program provides either a probabilistic verification statement in the aforementioned vein or a counterexample - an instance where the system went unsafe. To showcase our results, we verify the robotarium simulator, identify counterexamples for its hardware counterpart, and experimentally verify the safety of a multi-agent quadrupedal system
Local Normal Approximations and Probability Metric Bounds for the Matrix-Variate T Distribution and Its Application to Hotelling’s T Statistic
No full textIn this paper, we develop local expansions for the ratio of the centered matrix-variate T density to the centered matrix-variate normal density with the same covariances. The approximations are used to derive upper bounds on several probability metrics (such as the total variation and Hellinger distance) between the corresponding induced measures. This work extends some previous results for the univariate Student distribution to the matrix-variate setting
Rotation of Low-mass Stars in Upper Centaurus–Lupus and Lower Centaurus–Crux with TESS
No full textWe present stellar rotation rates derived from Transiting Exoplanet Survey Satellite (TESS) light curves for stars in Upper Centaurus–Lupus (UCL; ∼136 pc, ∼16 Myr) and Lower Centaurus–Crux (LCC; ∼115 pc, ∼17 Myr). We find spot-modulated periods (P) for ∼90% of members. The range of light-curve and periodogram shapes echoes that found for other clusters with K2, but fewer multiperiod stars may be an indication of the different noise characteristics of TESS, or a result of the source selection methods here. The distribution of P as a function of color as a proxy for mass fits nicely in between that for both older and younger clusters observed by K2, with fast rotators being found among both the highest and lowest masses probed here, and a well-organized distribution of M-star rotation rates. About 13% of the stars have an infrared excess, suggesting a circumstellar disk; this is well matched to expectations, given the age of the stars. There is an obvious pileup of disked M stars at P ∼ 2 days, and the pileup may move to shorter P as the mass decreases. There is also a strong concentration of disk-free M stars at P ∼ 2 days, hinting that perhaps these stars have recently freed themselves from their disks. Exploring the rotation rates of stars in UCL/LCC has the potential to help us understand the beginning of the end of the influence of disks on rotation, and the timescale on which stars respond to unlocking
SN 2009ip after a decade: the luminous blue variable progenitor is now gone
No full textWe present new Hubble Space Telescope (HST) imaging photometry for the site of the Type IIn supernova (SN) 2009ip taken almost a decade after explosion. The optical source has continued to fade steadily since the SN-like event in 2012. In the F606W filter, which was also used to detect its luminous blue variable (LBV) progenitor 13 yr before the SN, the source at the position of SN 2009ip is now 1.2 mag fainter than that quiescent progenitor. It is 6–7 mag fainter than the pre-SN outbursts in 2009–2011. This definitively rules out a prediction that the source would return to its previous state after surviving the 2012 event. Instead, the late-time fading matches expectations for a terminal explosion. The source fades at a similar rate in all visual-wavelength filters without significant colour changes, therefore also ruling out the hypothesis of a luminous dust-obscured survivor or transition to a hotter post-LBV survivor. The late-time continuum with steady colour and strong Hα emission detected in a narrow F657N filter are, however, entirely expected for ongoing shock interaction with circumstellar material in a decade-old core-collapse SN. Interestingly, the ultraviolet flux has stayed nearly constant since 2015, supporting previous conjectures that the F275W light traces main-sequence OB stars in an underlying young star cluster. We expect that the visual-wavelength continuum will eventually level off, tracing this cluster light. Without any additional outbursts, it seems prudent to consider the 2012 event as a terminal SN explosion, and we discuss plausible scenarios
ScaDL 2022 Invited Talk 3: Million-x speedups through convergence of AI and HPC
No full textMany scientific applications currently rely on the use of brute-force numerical methods performed on highperformance computing (HPC) infrastructure. However, these methods have their limits even with the growing hardware capabilities, e.g. for fine-scale climate prediction and large molecule quantum chemistry. Can artificial intelligence (AI) methods augment or even entirely replace these brute-force calculations to obtain million-x speed-ups? Can we make groundbreaking new discoveries because of such speed-ups? I will present exciting recent advances that build new foundations in AI that are applicable to a wide range of problems such as fluid dynamics and quantum chemistry
Highly Selective Electrocatalytic Oxidation of Amines to Nitriles Assisted by Water Oxidation on Metal-Doped α-Ni(OH)₂
No full textSelective oxidation to synthesize nitriles is critical for feedstock manufacturing in the chemical industry. Current strategies typically involve substitutions of alkyl halides with toxic cyanides or the use of strong oxidation reagents (oxygen or peroxide) under ammoxidation/oxidation conditions, setting considerable challenges in energy efficiency, sustainability, and production safety. Herein, we demonstrate a facile, green, and safe electrocatalytic route for selective oxidation of amines to nitriles under ambient conditions, assisted by the anodic water oxidation on metal-doped α-Ni(OH)₂ (a typical oxygen evolution reaction catalyst). By controlling the balance between co-adsorption of the amine molecule and hydroxyls on the catalyst surface, we demonstrate that Mn doping significantly promotes the subsequent chemical oxidation of amines, resulting in Faradaic efficiencies of 96% for nitriles under ≥99% conversion. This anodic oxidation is further coupled with cathodic hydrogen evolution for overall atomic economy and additional green energy production