In September 2016, Stanford's"One Hundred Year Study on Artificial Intelligence"project (AI100) issued the first report of its planned long-term periodic assessment of artificial intelligence (AI) and its impact on society. It was written by a panel of 17 study authors, each of whom is deeply rooted in AI research, chaired by Peter Stone of the University of Texas at Austin. The report, entitled"Artificial Intelligence and Life in 2030,"examines eight domains of typical urban settings on which AI is likely to have impact over the coming years: transportation, home and service robots, healthcare, education, public safety and security, low-resource communities, employment and workplace, and entertainment. It aims to provide the general public with a scientifically and technologically accurate portrayal of the current state of AI and its potential and to help guide decisions in industry and governments, as well as to inform research and development in the field. The charge for this report was given to the panel by the AI100 Standing Committee, chaired by Barbara Grosz of Harvard University.
Extremely low metallicity stars are intensely studied as they take observations the closest to the very first generations of stars in the universe. Widely assumed to be enriched by just one dying massive star, some of these very metal poor stars have abnormal chemical abundance ratios and have been taken to reflect a rare hypernova (with high explosion energy $\gtrsim \ 10^{52}$ erg.). Here we remodel the enrichment of three such stars and show that their abundances are better explained by enrichment from a normal (less energetic) supernova accounting for inhomogeneous distribution of the ejecta. This work establishes the importance of the inhomogeneity of supernovae, serves as a template for a required reassessment of all metal-poor/peculiar stars, and raises the need to quantify this inhomogeneity both in theory and in observations.
We present a dataset of high resolution spectra of the Sun of many strongly polarized lines belonging to the second solar spectrum, i.e. the spectrum near the limb in linear polarization (scattering polarization). These solar spectra were obtained in full Stokes polarimetry (I, Q/I, U/I, V/I) in the quiet Sun at various distances from the limb, and at disk centre for comparison, with the ground based CNRS THEMIS telescope. Polarization rates Q/I up to 7% are obtained in CaI 4227 Å line at $μ$ = cos$θ$ = 0, while 2% is reached in SrI 4607 Å line and 1.4% in BaII 4554 Å. The spectra shown here are freely available in FITS format to the research community.
Galáxias são estruturas fundamentais no Universo. A descoberta da natureza extragaláctica das nebulosas espirais só ocorreu em meados dos anos 1920. Durante o século que se passou desde então, aprendemos muito sobre as galáxias. Este texto descreve como chegamos à conclusão de que o Universo é povoado de galáxias, muitas semelhantes à nossa própria, a Via Láctea. Veremos como classificamos as galáxias, quais são suas principais propriedades, como elas se formam e evoluem, e como estão distribuídas pelo Universo.
A experiência de dar aula em São Paulo no ano anterior à mudança para Nova York em 1998 foi fundamental para instigar a necessidade de trabalhar com um pseudônimo. Percebemos nas aulas na FAAP (1997-1998) que não só nós estávamos influenciando os alunos como eles também nos influenciavam. Começou a surgir ali, embrionária ainda, a ideia de “contaminação” que permeia nossa prática até hoje: contaminar e ser contaminado. Percebemos então que nunca estamos sozinhos e que a melhor forma de abraçar igualmente todas as pessoas envolvidas num projeto é usar um pseudônimo. Em 1997 criamos então nosso primeiro codinome – feito para um projeto específico de cartões-postais “falsos” da cidade de São Paulo (que eram inseridos clandestinamente em bancas de jornal da cidade e vendidos como cartões turísticos comuns): Diamantino. A ideia principal para a utilização do pseudônimo nesse projeto era que esses cartões-postais não fossem percebidos como “arte”.
Low-density and unbound stellar groups, OB associations have been historically delineated through their bright and massive members. They have been analysed for decades, but the arrival of Hipparcos, and more recently of Gaia led to a change of paradigm by allowing the identification of more reliable members using parallaxes and proper motions. This renewed interest offers an opportunity to emphasize the role of OB associations across many areas of astronomy. In this review, I highlight their importance across multiple scales: how OB associations constitute suitable sites to study massive stars and stellar multiplicity, their relation with star clusters, their interactions with the interstellar medium through the feedback of their massive members, and how they shape the structure and evolution of the Milky Way and beyond.
Abstract ASTRO-DF is a prominent trust-region method using adaptive sampling for stochastic derivative-free optimization of nonconvex problems. Its salient feature is an easy-to-understand-and-implement concept of maintaining “just enough” replications when evaluating points throughout the search to guarantee almost-sure convergence to a first-order critical point. To reduce the dependence of ASTRO-DF on the problem dimension and boost its performance in finite time, we present two key refinements, namely: (i) local models with diagonal Hessians constructed on interpolation points based on a coordinate basis; and (ii) direct search using the interpolation points whenever possible. We demonstrate that the refinements in (i) and (ii) retain the convergence guarantees while matching existing results on iteration complexity. Uniquely, our iteration complexity results match the canonical rates without placing assumptions on iterative models’ quality and their independence from function estimates. Numerical experimentation on a testbed of problems and comparison against existing popular algorithms reveals the computational advantage of ASTRO-DF due to the proposed refinements.
Despite centuries of rigorous theoretical and observational research, the origin and acceleration mechanism of Galactic Cosmic Rays (GCRs) remain a mystery. In 1949, Fermi proposed a diffusive shock acceleration model that includes a prominent mechanism for GCR acceleration. However, observational evidence, on the other hand, remains elusive. Here, we provided the first apparent verification of GCR acceleration at 1 AU using measurements from the CRIS instrument onboard the ACE spacecraft.
Nicholas Flinner, Michael A. Tucker, John F. Beacom
et al.
We analyze pre-explosion ultraviolet (UV) imaging of the nearby Type II supernova SN 2023ixf in search of precursor variability. No outbursts are seen in observations obtained 15-20 yr prior to explosion to a limit of $L_{NUV} \approx 1000~L_{sun}$ and $L_{NUV} \approx 2000~L_{sun}$. The time period of these non-detections roughly corresponds to changes in the circumstellar density inferred from early spectra and photometry.
Stars' chemical signatures provide invaluable insights into stellar cluster formation. This study utilized the Weisfeiler-Lehman (WL) Graph Kernel to examine a 15-dimensional elemental abundance space. Through simulating chemical distributions using normalizing flows, the effectiveness of our algorithm was affirmed. The results highlight the capability of the WL algorithm, coupled with Gaussian Process Regression, to identify patterns within elemental abundance point clouds correlated with various cluster mass functions. Notably, the WL algorithm exhibits superior interpretability, efficacy and robustness compared to deep sets and graph convolutional neural networks and enables optimal training with significantly fewer simulations (O(10)), a reduction of at least two orders of magnitude relative to graph neural networks.
We have investigated the chemistry of dense interstellar clouds and found new bistable solutions in the nitrogen and carbon chemistries. We identify the autocatalytic processes that are present in the pure, reduced, chemical networks and, as previously found for oxygen chemistry, that He$^+$ plays an important role. The applicability of these results to astronomical environments is briefly discussed. The bistable solutions found for carbon chemistry occur for low densities and high ionization fractions that are not compatible with that found cold, dense clouds. Bistability in the pure nitrogen chemistry occurs for conditions that are relevant for prestellar cores in which significant CO depletion has taken place. We conclude that several autocatalyses are embedded in gas-phase interstellar chemistry and that many more are potentially present.
For centuries, humanity wondered if there were other worlds like ours in the Universe. For about a quarter of a century, we have known that planetary systems exist around other stars, and more than 3800 exoplanetary systems have been discovered so far. However, the large majority of the exoplanets remain invisible to us since we usually infer their presence by their effect on their star. The chapter is devoted to stellar hosts and their characteristics, emphasizing their description by discovery method and links between the properties of the host stars and their planets. The star-planet connection is vital to constrain the theories on the formation and evolution of planetary systems, including our own.
We report a new binary black hole merger in the publicly available LIGO First Observing Run (O1) data release. The event has an inverse false alarm rate of one per six years in the detector-frame chirp-mass range $\mathcal{M}^{\rm det} \in [20,40]M_\odot$ in a new independent analysis pipeline that we developed. Our best estimate of the probability that the event is of astrophysical origin is $P_{\rm astro} \sim 0.71\, .$ The estimated physical parameters of the event indicate that it is the merger of two massive black holes, $\mathcal{M}^{\rm det} = 31^{+2}_{-3}\,M_\odot$ with an effective spin parameter, $\chi_{\rm eff} = 0.81^{+0.15}_{-0.21}$, making this the most highly spinning merger reported to date. It is also among the two highest redshift mergers observed so far. The high aligned spin of the merger supports the hypothesis that merging binary black holes can be created by binary stellar evolution.
Time-series photometry in I and J band of 57 inner Galactic late-type stars, highly-probable red supergiant (RSG) stars, is here presented. 38% of the sample presents significant photometric variations. The variations in I and J band appear to be correlated, with DeltaI = DeltaJ x 2.2, DeltaI variations ranging from 0.04-1.08 mag, DeltaJ variations from 0.03-0.52 mag. New short periods (< 1000 d) could be estimated for 8 stars and range from 167-433 d. This work confirms that the sample is not contaminated by large-amplitude Asymptotic Giant Branch (AGB) stars. Furthermore, despite the large errors in distance, the period-luminosity diagram suggests that the sample is populating the same sequence as the known Galactic RSGs.
We performed population synthesis simulations of Population III binary stars with Maxwellian kick velocity distribution when MGCOs (Mass Gap Compact Objects with mass 2--5$\,M_{\odot}$) are formed. We found that for eight kick velocity dispersion models of $σ_{\rm k}=0$--$500$ km/s, the mean mass of black hole (BH)-MGCO binary is $\sim (30 \,M_\odot,\,2.6 \,M_\odot)$. In numerical data of our simulations, we found the existence of BH-MGCO binary with mass $(22.9 \,M_\odot,\,2.5 \,M_\odot)$ which looks like GW190814.
Recent observations suggest the presence of supermassive black holes at the centers of many galaxies. The existence of intermediate-mass black holes (IMBHs) in globular clusters has also been predicted. We focus on gravitational lensing as a new way to explore these entities. It is known that the mass distribution of a self-gravitating system such as a globular cluster changes greatly depending on the presence or absence of a central massive object. After considering possible mass distributions for a globular cluster belonging to the Milky Way galaxy, we estimate that the effect on the separation angle of gravitational lensing due to an IMBH would be of milliarcsecond order.
We use APEX mapping observations of 13CO, and C18O (2-1) to investigate the internal gas kinematics of the filamentary cloud G350.54+0.69, composed of the two distinct filaments G350.5-N and G350.5-S. G350.54+0.69 as a whole is supersonic and gravitationally bound. We find a large-scale periodic velocity oscillation along the entire G350.5-N filament with a wavelength of ~1.3 pc and an amplitude of ~0.12 km/s. Comparing with gravitational-instability induced core formation models, we conjecture that this periodic velocity oscillation could be driven by a combination of longitudinal gravitational instability and a large-scale periodic physical oscillation along the filament. The latter may be an example of an MHD transverse wave. This hypothesis can be tested with Zeeman and dust polarization measurements.