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Optical tracking systems typically trade off between astrometric precision and field of view. In this work, we showcase a networked approach to optical tracking using very wide field-of-view imagers that have relatively low astrometric precision on the scheduled OSIRIS-REx slingshot manoeuvre around Earth on 22 Sep 2017. As part of a trajectory designed to get OSIRIS-REx to NEO 101955 Bennu, this flyby event was viewed from 13 remote sensors spread across Australia and New Zealand to promote triangulatable observations. Each observatory in this portable network was constructed to be as lightweight and portable as possible, with hardware based off the successful design of the Desert Fireball Network. Over a 4-h collection window, we gathered 15 439 images of the night sky in the predicted direction of the OSIRIS-REx spacecraft. Using a specially developed streak detection and orbit determination data pipeline, we detected 2 090 line-of-sight observations. Our fitted orbit was determined to be within about 10 km of orbital telemetry along the observed 109 262 km length of OSIRIS-REx trajectory, and thus demonstrating the impressive capability of a networked approach to Space Surveillance and Tracking.
Richard Price (1723–91) is important in present-day historiography chiefly for the interpretation of two great revolutions, the American and the French. Recent studies have depicted him as insightfully forward-looking, a well-informed cosmopolitan, his thought providing an interpretive key to the Age of Revolutions, and so as a landmark figure of a singular Enlightenment. They have paid insufficient attention to his identity as a theologian, a Welsh-born Nonconformist minister of more defined outlook, spending his life in England and campaigning above all for the relief of Nonconformist grievances, picturing “tyranny” and “superstition” in conventional Nonconformist terms. This article offers a reconsideration of the significance of such a Price for the historical understanding of two major and (it contends) related problems: how did the American Revolution relate to the French in a supposed Age of Revolutions, and how should they be understood as putative episodes in the development of the Enlightenment?
Much remains unknown about how the 2008 Great Recession, coupled with the ageing baby-boomer cohort, have shaped retirement expectations and realised retirement timing across diverse groups of older Americans. Using the Health and Retirement Study (1992–2016), we compared expectations about full-time work at age 62 (reported at ages 51–61) with realised labour force status at age 62. Of the 12,049 respondents, 34 per cent reported no chance of working full time at 62 (zero probability) and 21 per cent reported it was very likely (90–100 probability). Among those reporting no chance of working, there was a 0.111 probability of unmet expectations; among those with high expectations of working, there was a 0.430 probability of unmet expectations. Black and Hispanic Americans were more likely than white Americans to have unmet expectations of both types. Educational attainment was associated with higher probability of unexpectedly working and lower probability of unexpectedly not working. Baby-boomers experienced fewer unmet expectations than prior cohorts but more uncertainty about work status at 62. Our findings highlight the unpredictability of retirement timing for significant segments of the US population and the role of the Great Recession in contributing to uncertainty. Given the individual and societal benefits of long work lives, special attention should be paid to the high rates of unexpectedly not working at age 62.
Gravitational waves from coalescing neutron stars encode information about nuclear matter at extreme densities, inaccessible by laboratory experiments. The late inspiral is influenced by the presence of tides, which depend on the neutron star equation of state. Neutron star mergers are expected to often produce rapidly rotating remnant neutron stars that emit gravitational waves. These will provide clues to the extremely hot post-merger environment. This signature of nuclear matter in gravitational waves contains most information in the 2–4 kHz frequency band, which is outside of the most sensitive band of current detectors. We present the design concept and science case for a Neutron Star Extreme Matter Observatory (NEMO): a gravitational-wave interferometer optimised to study nuclear physics with merging neutron stars. The concept uses high-circulating laser power, quantum squeezing, and a detector topology specifically designed to achieve the high-frequency sensitivity necessary to probe nuclear matter using gravitational waves. Above 1 kHz, the proposed strain sensitivity is comparable to full third-generation detectors at a fraction of the cost. Such sensitivity changes expected event rates for detection of post-merger remnants from approximately one per few decades with two A+ detectors to a few per year and potentially allow for the first gravitational-wave observations of supernovae, isolated neutron stars, and other exotica.
It has been widely speculated that dominant motifs, such as short-range icosahedral order, can influence glass formation and the properties of glasses. Experimental data on both fragile and strong undercooled liquids show corresponding changes in their thermophysical properties consistent with increasing development of a network of interconnect motifs based on molecular dynamics. Describing these regions of local order, how they connect, and how they are related to property changes have been challenging issues, both computationally and experimentally. Yet the consensus is that metallic liquids develop interconnected medium-range order consisting of some regions with lower mobility with deeper undercooling. Less well understood is how these motifs (or “crystal genes”) in the liquid can inhibit nucleation in the deeply undercooled liquid or influence phase selection upon devitrification. These motifs tend to have local packing unlike stable compounds with icosahedral order tending to dominate the best glass formers. The underlying kinetic and thermodynamic forces that guide the formation of these motifs and how they interconnect during undercooling remain open questions.
Through diversity of composition, sequence, and interfacial structure, hybrid materials greatly expand the palette of materials available to access novel functionality. The NSF Division of Materials Research recently supported a workshop (October 17–18, 2019) aiming to (1) identify fundamental questions and potential solutions common to multiple disciplines within the hybrid materials community; (2) initiate interfield collaborations between hybrid materials researchers; and (3) raise awareness in the wider community about experimental toolsets, simulation capabilities, and shared facilities that can accelerate this research. This article reports on the outcomes of the workshop as a basis for cross-community discussion. The interdisciplinary challenges and opportunities are presented, and followed with a discussion of current areas of progress in subdisciplines including hybrid synthesis, functional surfaces, and functional interfaces.
Additive manufacturing (AM) comprises a group of transformative technologies that are likely to revolutionize manufacturing. In particular, laser-based metal AM techniques can not only fabricate parts with extreme complexity, but also provide innovative means for designing and processing new metallic systems. However, there are still several technical barriers that constrain metal AM. Overcoming these barriers requires a better understanding of the physics underlying the complex and dynamic laser–metal interaction at the heart of many AM processes. This article briefly describes the state of the art of in situ/operando synchrotron x-ray imaging and diffraction for studying metal AM, mostly the laser powder-bed fusion process. It highlights the immediate impact of operando synchrotron studies on the advancement of AM technologies, and presents future research challenges and opportunities.
Solidification processing offers the first opportunity to control microstructure, properties, and performance in metallic alloy components. Until recently, microstructural evaluations were limited to post-solidification characterization by destructive methods. We review the development of time-resolved, in situ imaging techniques capable of capturing solid–liquid interfacial evolution in metallic alloys with high spatial and temporal resolution under diverse solidification conditions relevant for applications ranging from conventional directional solidification, crystal growth, and casting, to welding and additive manufacturing. These experiments enable direct visualization of transient behaviors that would otherwise remain unknown, uniquely providing insights into the physics that impact microstructure and defect development, and strategies for microstructural control and defect mitigation. Understanding microstructural evolution and the characteristics that form under various solidification conditions is essential for the development of multiscale, experimentally informed predictive modeling. This is highlighted by solidification simulations that utilize in situ measurements of solidification dynamics from state-of-the-art experimental techniques.
The field of solidification has evolved from metallurgical alchemy to a predictive science over the past century. Our particular focus is on metals and their alloys, whose thermophysical properties tend to differ distinctively from that of organic systems. Rapid advances in modeling efforts and real-time experiments have yielded a wealth of new and quantitative information across relevant length- and time scales, thereby expanding our understanding of the liquid-to-solid phase transition. The articles in this issue highlight some important recent developments in the field, including solidification at extreme rates, as well as the state-of-the-art computational and experimental techniques that allow us to probe the otherwise improbable. In light of this progress, we identify critical issues and open questions that point to future research directions in solidification science.
Synchrotron x-rays are a powerful tool to probe real-time changes in the microstructure of materials as they respond to an external stimulus, such as phase transformations that take place in response to a change in temperature. X-ray imaging techniques include radiography and tomography, and have been steadily improved over the last decades so that they can now resolve micrometer-scale or even finer structural changes in bulk specimens over time scales of a second or less. Under certain conditions, these imaging approaches can also give spatially resolved chemical information. In this article, we focus on the liquid to solid transformation of metallic alloys and the temporal and spatial resolution of the accompanying segregation of alloying elements. The solidification of alloys provides an excellent case study for x-ray imaging because it is usually accompanied by the progressive, preferential segregation of one or more of the alloying elements to either the solid or the liquid, and gives rise to surprisingly complex chemical segregation patterns. We describe chemical mapping investigations of binary and quasi-binary alloys using radiography and tomography, and recent developments in x-ray fluorescence imaging that offer the prospect of a more general, multielement mapping technique. Future developments for synchrotron-based chemical mapping are also considered.