Unequal Cities Benjamins, Maureen R; De Maio, Fernando G; Morita, Julie
2021
eBook
Prachand, Pamela T. Roesch, Michael Rozier, Nazia Saiyed, Eve Shapiro, Abigail Silva, Veenu Verma, the West Side United Metrics Working Group, Ruqaiijah Yearby.
We investigate the responsiveness of the 2798AA Mg II broad emission line in AGN on timescales of several years. Our study is based on a sample of extremely variable AGN as well as a broad population ...sample. The observed response of the line in previous studies has been mixed. By focussing on extreme variability (\(|\Delta g|>\) 1) we find that Mg II clearly does respond to the continuum. However, the degree of responsiveness varies strikingly from one object to another; we see cases of Mg II changing by as much as the continuum, more than the continuum, or very little at all. In 74% of the highly variable sample the behaviour of Mg II corresponds with that of H\(\beta\), with 30% of the objects showing large variations in both lines. We do not detect any change in the line width that would correspond to Broad Line Region `breathing', in accordance with results from literature. Some of the objects in our highly variable sample show a clear asymmetry in the Mg II profile. This skewness can be both to the blue and the red of the line centre. Results from our broad population sample show that highly variable quasars have lower Eddington ratios. This result holds for the variability of the continuum, but the correlation is significantly reduced for the variability of the Mg II line. For the first time, we present an overview of the value of the intrinsic Baldwin Effect for Mg II in a large sample.
The time and cost associated with the development and certification of flight-critical software have been escalating at an alarming rate for modern, software-enabled air vehicles. This upward trend ...is expected to continue as future vehicles will be increasingly autonomous and intelligent. Affordable, efficient processes and tools are needed to control development costs and schedule, as well as to ensure the safety of these vehicles. This paper presents the results of a U. S. Air Force Research Laboratory (AFRL) sponsored project on the development of validation and verification (V&V) technologies for flight-critical software. The purpose of the project is to improve the affordability and safety for software V&V, specifically, for adaptive and/or mixed-criticality software. Adaptive software introduces uncertainties; mixed-criticality refers to the information passed between flight critical and mission critical software partitions, hence affecting in-flight adaptation (or control reconfiguration). The methodology developed in this project strongly suggests that an integrated, model-based approach be used in the V&V of adaptive software. In this approach, the same physical model is used for design, implementation, and testing, while emphasis has been placed on checking the uncertainty and the accuracy of the models, which often are implemented in flight control and health management software. In the paper, we use a scenario to illustrate the capabilities of the proposed V&V methodology. The scenario describes an unmanned air vehicle (UAV) executing an autonomous aerial refueling mission.
We report the discovery of a new ``changing-look'' active galactic nucleus (CLAGN) event, in the quasar SDSS J162829.17+432948.5 at z=0.2603, identified through repeat spectroscopy from the fifth ...Sloan Digital Sky Survey (SDSS-V). Optical photometry taken during 2020--2021 shows a dramatic dimming of \({\Delta}\)g\({\approx}\)1 mag, followed by a rapid recovery on a timescale of several months, with the \({\lesssim}\)2 month period of rebrightening captured in new SDSS-V and Las Cumbres Observatory spectroscopy. This is one of the fastest CLAGN transitions observed to date. Archival observations suggest that the object experienced a much more gradual dimming over the period of 2011--2013. Our spectroscopy shows that the photometric changes were accompanied by dramatic variations in the quasar-like continuum and broad-line emission. The excellent agreement between the pre- and postdip photometric and spectroscopic appearances of the source, as well as the fact that the dimmest spectra can be reproduced by applying a single extinction law to the brighter spectral states, favor a variable line-of-sight obscuration as the driver of the observed transitions. Such an interpretation faces several theoretical challenges, and thus an alternative accretion-driven scenario cannot be excluded. The recent events observed in this quasar highlight the importance of spectroscopic monitoring of large active galactic nucleus samples on weeks-to-months timescales, which the SDSS-V is designed to achieve.
Future U.S. Air Force capabilities will rely on mixed manned/unmanned vehicles working together as a team. These vehicles will be increasingly autonomous, capable of on-board decision-making and ...mission re-planning, and yet interoperable to complete a desired mission safely, reliably, and adaptively. A key enabler of this cooperative airspace is adaptive or reconfigurable control software. This kind of software poses a strong challenge to the verification and validation (V&V) process, which leads to the final certification and accreditation of the software. Traditional V&V processes rely heavily on testing or other informal methods. These processes are time consuming and increasingly expensive as the complexity of the software increases. Alternative processes that can increase affordability while applying more formal methods have been attractive recently. This paper describes a formal software checking method by using the Karnaugh Map technique. This method checks the consistency and completeness of the software during the verification process. A proof-of-concept test of the method has been applied to an aircraft actuation system. The C-language source code of the actuator system used as a model in an adaptive flight control system is checked by the method. The preliminary results of this proof of concept are presented in this paper. The results demonstrated the feasibility of the method. The results are consistent with previous applications of the method to other sophisticated software systems, such as semiconductor manufacturing and command & control systems. Continued maturation of this process and technology is being supported by the Air Force Research Laboratory.
An integrated system bench has been developed for validating system process using real-time simulation model. The validation process performs the feature characterization of a dynamical system of ...interest, and then uses the characterized features for system performance validation. The system bench is a computer platform consisting of multiple single-board computers, in which a suite of real-time embedded algorithms is designed and dedicated to system performance validation and fault feature analysis. The overall functionality of the system bench is to provide a versatile, robust, and real-time working environment for system model performance validation, in which a number of software tools can be invoked for system model integrity analysis and run-time performance identification.
Active galactic nuclei (AGN) that show strong rest-frame optical/UV variability in their blue continuum and broad line emission are classified as "changing-look" AGN, or at higher luminosities ...changing look quasars (CLQs). These surprisingly large and sometimes rapid transitions challenge accepted models of quasar physics and duty cycles, offer several new avenues for study of quasar host galaxies, and open a wider interpretation of the cause of differences between broad and narrow line AGN. To better characterize extreme quasar variability, we present follow-up spectroscopy as part of a comprehensive search for CLQs across the full SDSS footprint using spectroscopically confirmed quasars from the SDSS DR7 catalog. Our primary selection requires large-amplitude (|\Delta g|>1 mag, |\Delta r|>0.5 mag) variability over any of the available time baselines probed by the SDSS and Pan-STARRS 1 surveys. We employ photometry from the Catalina Sky Survey to verify variability behavior in CLQ candidates where available, and confirm CLQs using optical spectroscopy from the William Herschel, MMT, Magellan, and Palomar telescopes. For our adopted S/N threshold on variability of broad H\beta emission, we find 17 new CLQs, yielding a confirmation rate of >~ 20%. These candidates are at lower Eddington ratio relative to the overall quasar population which supports a disk-wind model for the broad line region. Based on our sample, the CLQ fraction increases from 10% to roughly half as the continuum flux ratio between repeat spectra at 3420 Angstroms increases from 1.5 to 6. We release a catalog of over 200 highly variable candidates to facilitate future CLQ searches.
Web services technology is poised to make its greatest contributions as an enabler in the evolution from conventional, distributed computing to service-centric computing. Service-centric computing ...provides a high-level model for how applications can be assembled from a distributed network of constituent parts, and Web services contribute the nuts and bolts details for technical implementation. The service-centric model also creates a new ecosystem of interrelated suppliers and consumers of not just technology but information. It does so by providing access to distributed services, which themselves serve as information providers. The ecosystem being created around this Web of information providers and consumers include software vendors, application service providers, publishers, exchanges and standards bodies.
