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PDRs4All: A JWST Early Release Science Program on Radiative Feedback from Massive Stars
No full textMassive stars disrupt their natal molecular cloud material through radiative and mechanical feedback processes. These processes have profound effects on the evolution of interstellar matter in our Galaxy and throughout the universe, from the era of vigorous star formation at redshifts of 1–3 to the present day. The dominant feedback processes can be probed by observations of the Photo-Dissociation Regions (PDRs) where the far-ultraviolet photons of massive stars create warm regions of gas and dust in the neutral atomic and molecular gas. PDR emission provides a unique tool to study in detail the physical and chemical processes that are relevant for most of the mass in inter- and circumstellar media including diffuse clouds, proto-planetary disks, and molecular cloud surfaces, globules, planetary nebulae, and star-forming regions. PDR emission dominates the infrared (IR) spectra of star-forming galaxies. Most of the Galactic and extragalactic observations obtained with the James Webb Space Telescope (JWST) will therefore arise in PDR emission. In this paper we present an Early Release Science program using the MIRI, NIRSpec, and NIRCam instruments dedicated to the observations of an emblematic and nearby PDR: the Orion Bar. These early JWST observations will provide template data sets designed to identify key PDR characteristics in JWST observations. These data will serve to benchmark PDR models and extend them into the JWST era. We also present the Science-Enabling products that we will provide to the community. These template data sets and Science-Enabling products will guide the preparation of future proposals on star-forming regions in our Galaxy and beyond and will facilitate data analysis and interpretation of forthcoming JWST observations
Intertemporal choice experiments and large-stakes behavior
No full textIntertemporal choice experiments are increasingly implemented to make inference about discounting and marginal utility, yet little is known about the predictive power of resulting measures. This project links standard experimental choices to a consumption smoothing decision with large stakes — around 10% of annual income. In a sample of around 400 Guatemalan Conditional Cash Transfer recipients, we find that preferences over large-stakes payment plans are significantly correlated with experimental measures of patience and diminishing marginal utility. These represent the first findings in the literature on the predictive content of such experimentally elicited measures for a large-stakes decision
A potential two-scale traveling wave singularity for 3D incompressible Euler equations
No full textIn this paper, we investigate a potential two-scale traveling wave singularity of the 3D incompressible axisymmetric Euler equations with smooth initial data of finite energy. The two-scale feature is characterized by the property that the center of the traveling wave approaches to the origin at a slower rate than the rate of the collapse of the singularity. The driving mechanism for this potential singularity is due to two antisymmetric vortex dipoles that generate a strong shearing layer in both the radial and axial velocity fields. Without any viscous regularization, the 3D Euler equations develop an additional small scale characterizing the thickness of the sharp front. In order to stabilize the rapidly decreasing thickness of the sharp front, we apply a vanishing first order numerical viscosity to the Euler equations. We present numerical evidence that the 3D Euler equations with this first order numerical viscosity develop a locally self-similar blowup at the origin
Dust Evolution in the Coma of Distant, Inbound Comet C/2017 K2 (PANSTARRS)
No full textC/2017 K2 (PANSTARRS) is an Oort Cloud comet previously observed to be active at heliocentric distances r > 20 au on what is likely its first passage through the inner solar system. We observed the comet on 2021 March 19–20 at r = 6.82 au preperihelion and 8.°35 phase angle with the Hubble Space Telescope (HST), and obtained high spatial resolution photometry and polarimetry mapping the properties of dust over the coma prior to the onset of water ice sublimation activity on the nucleus. We found clear radial gradients in the color and polarization of the coma: the F475W–F775W (g' - i') reflectance slope increased from ∼4.5% per 100 nm within ∼10,000 km of the nucleus up to ∼7% per 100 nm by ∼50,000 km, while the negative polarization in F775W (i') strengthened from about −2% to −3.5% over the same range. The radial intensity profiles moreover strongly deviate from profiles simulated for stable dust grains. Near-infrared imagery obtained with the Palomar Hale Telescope on 2021 May 18 at r = 6.34 au revealed a continued absence of micron-sized grains in the tail, but showed no clear spatial gradient in JHKₛ colors. The observed patterns collectively appear consistent with the inner coma being optically dominated by sublimating, micron-sized water ice grains, unlike the tail of more stable, millimeter-sized grains. Finally, we evaluated these results alongside other Oort Cloud comets, and found in a reanalysis of HST observations of C/2012 S1 (ISON) that the near-nucleus polarimetric halo reported for that comet is likely an observational artifact
Kinetically Constrained Quantum Dynamics in Superconducting Circuits
No full textWe study the dynamical properties of the bosonic quantum East model at low temperature. We show that a naive generalization of the corresponding spin-1/2 quantum East model does not possess analogous slow dynamical properties. In particular, conversely to the spin case, the bosonic ground state turns out to be not localized. We restore localization by introducing a repulsive interaction term. The bosonic nature of the model allows us to construct rich families of many-body localized states, including coherent, squeezed, and cat states. We formalize this finding by introducing a set of superbosonic creation-annihilation operators that satisfy the bosonic commutation relations and, when acting on the vacuum, create excitations that are exponentially localized around a certain site of the lattice. Given the constrained nature of the model, these states retain memory of their initial conditions for long times. Even in the presence of dissipation, we show that quantum information remains localized within decoherence times that are tunable with the parameters of the system. We propose an implementation of the bosonic quantum East model based on state-of-the-art superconducting circuits, which could be used in the near future to explore the dynamical properties of kinetically constrained models in modern platforms
Apophis Planetary Defense Campaign
No full textWe describe results of a planetary defense exercise conducted during the close approach to Earth by the near-Earth asteroid (99942) Apophis during 2020 December–2021 March. The planetary defense community has been conducting observational campaigns since 2017 to test the operational readiness of the global planetary defense capabilities. These community-led global exercises were carried out with the support of NASA’s Planetary Defense Coordination Office and the International Asteroid Warning Network. The Apophis campaign is the third in our series of planetary defense exercises. The goal of this campaign was to recover, track, and characterize Apophis as a potential impactor to exercise the planetary defense system including observations, hypothetical risk assessment and risk prediction, and hazard communication. Based on the campaign results, we present lessons learned about our ability to observe and model a potential impactor. Data products derived from astrometric observations were available for inclusion in our risk assessment model almost immediately, allowing real-time updates to the impact probability calculation and possible impact locations. An early NEOWISE diameter measurement provided a significant improvement in the uncertainty on the range of hypothetical impact outcomes. The availability of different characterization methods such as photometry, spectroscopy, and radar provided robustness to our ability to assess the potential impact risk
Scattering and absorbing aerosols in the climate system
No full textTropospheric anthropogenic aerosols contribute the second-largest forcing to climate change, but with high uncertainty owing to their spatio-temporal variability and complicated optical properties. In this Review, we synthesize understanding of aerosol observations and their radiative and climate effects. Aerosols offset about one-third of the warming effect by anthropogenic greenhouse gases. Yet, in regions and seasons where the absorbing aerosol fraction is high — such as South America and East and South Asia — substantial atmospheric warming can occur. The internal mixing and the vertical distribution of aerosols, which alters both the direct effect and aerosol–cloud interactions, might further enhance this warming. Despite extensive research in aerosol–cloud interactions, there is still at least a 50% spread in total aerosol forcing estimates. This ongoing uncertainty is linked, in part, to the poor measurement of anthropogenic and natural aerosol absorption, as well as the little-understood effects of aerosols on clouds. Next-generation, space-borne, multi-angle polarization and active remote sensing, combined with in situ observations, offer opportunities to better constrain aerosol scattering, absorption and size distribution, thus, improving models to refine estimates of aerosol forcing and climate effects
New minerals in type A inclusions from Allende and clues to processes in the early solar system: Paqueite, Ca₃TiSi₂(Al,Ti,Si)₃O₁₄, and burnettite, CaVAlSiO₆
No full textPaqueite (Ca₃TiSi₂[Al,Ti,Si]₃O₁₄; IMA 2013-053) and burnettite (CaVAlSiO₆; IMA 2013-054) are new refractory minerals, occurring as euhedral to subhedral crystals within aluminous melilite in A-WP1, a type A Ca-Al-rich inclusion, and CGft-12, a compact type A (CTA) from the Allende CV3 carbonaceous chondrite. Type paqueite from A-WP1 has an empirical formula of (Ca_(2.91)Na_(0.11))Ti⁴⁺Si₂(Al_(1.64)Ti⁴⁺_(0.90)Si_(0.24)V³⁺_(0.12)Sc_(0.07)Mg_(0.03))O₁₄, with a trigonal structure in space group P321 and cell parameters a = 7.943 Å, c = 4.930 Å, V = 269.37 Å3, and Z = 1. Paqueite’s general formula is Ca₃TiSi₂(Al,Ti,Si)₃O₁₄ and the endmember formula is Ca₃TiSi₂(Al₂Ti)O₁₄. Type burnettite from CGft-12 has an empirical formula of Ca_(1.01)(V³⁺_(0.56)Al_(0.25)Mg_(0.18))(Si_(1.19)Al_(0.81))O₆. It assumes a diopside-type C2/c structure with a = 9.80 Å, b = 8.85 Å, c = 5.36 Å, β = 105.6°, V = 447.7 ų, and Z = 4. Burnettite’s general formula is Ca(V,Al,Mg)AlSiO₆ and the endmember formula is CaVAlSiO₆. Paqueite and burnettite likely originated as condensates, but the observed grains may have crystallized from local V-rich melts produced during a later thermal event. For CGft-12, the compositions of paqueite, clinopyroxene, and perovskite suggest that type As drew from two distinct populations of grains. Hibonite grains drew from multiple populations, but these were well mixed and not equilibrated prior to incorporation into type A host melilite
Survival of newly formed particles in haze conditions
No full textIntense new particle formation events are regularly observed under highly polluted conditions, despite the high loss rates of nucleated clusters. Higher than expected cluster survival probability implies either ineffective scavenging by pre-existing particles or missing growth mechanisms. Here we present experiments performed in the CLOUD chamber at CERN showing particle formation from a mixture of anthropogenic vapours, under condensation sinks typical of haze conditions, up to 0.1 s⁻¹. We find that new particle formation rates substantially decrease at higher concentrations of pre-existing particles, demonstrating experimentally for the first time that molecular clusters are efficiently scavenged by larger sized particles. Additionally, we demonstrate that in the presence of supersaturated gas-phase nitric acid (HNO₃) and ammonia (NH₃), freshly nucleated particles can grow extremely rapidly, maintaining a high particle number concentration, even in the presence of a high condensation sink. Such high growth rates may explain the high survival probability of freshly formed particles under haze conditions. We identify under what typical urban conditions HNO₃ and NH₃ can be expected to contribute to particle survival during haze
Safety and Efficiency in Robotics: The Control Barrier Functions Approach
No full textThis article aims at presenting an introductory overview of the theoretical framework of control barrier functions (CBFs) and of their application to the design of safety-related controllers for robotic systems. The article starts by describing the basic concepts of CBFs and how they can be used to build optimization problems embedding CBF-based constraints, whose solutions correspond to the control input enforcing the desired safety properties into the behavior of the controlled system. Simple examples, understandable for readers with a basic background in control theory and accompanied with source code for their simulation, are used to highlight the appealing features of the CBF-based approach. Then, more complex formulations applicable to robotic manipulators are introduced, recalling recent literature results allowing users to implement a robust design methodology. Finally, it is shown that CBFs are suitable for the implementation of safe human–robot collaboration in a realistic industrial scenario by means of the experimental validation in an industrial setup for collaborative robotics