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Here we present stringent low-frequency (185 MHz) limits on coherent radio emission associated with a short-duration gamma-ray burst (SGRB). Our observations of the short gamma-ray burst (GRB) 180805A were taken with the upgraded Murchison Widefield Array (MWA) rapid-response system, which triggered within 20s of receiving the transient alert from the Swift Burst Alert Telescope, corresponding to 83.7 s post-burst. The SGRB was observed for a total of 30 min, resulting in a
persistent flux density upper limit of 40.2 mJy beam–1. Transient searches were conducted at the Swift position of this GRB on 0.5 s, 5 s, 30 s and 2 min timescales, resulting in
limits of 570–1 830, 270–630, 200–420, and 100–200 mJy beam–1, respectively. We also performed a dedispersion search for prompt signals at the position of the SGRB with a temporal and spectral resolution of 0.5 s and 1.28 MHz, respectively, resulting in a
fluence upper-limit range from 570 Jy ms at DM
pc cm–3 (
) to 1 750 Jy ms at DM
pc cm–3 (
, corresponding to the known redshift range of SGRBs. We compare the fluence prompt emission limit and the persistent upper limit to SGRB coherent emission models assuming the merger resulted in a stable magnetar remnant. Our observations were not sensitive enough to detect prompt emission associated with the alignment of magnetic fields of a binary neutron star just prior to the merger, from the interaction between the relativistic jet and the interstellar medium (ISM) or persistent pulsar-like emission from the spin-down of the magnetar. However, in the case of a more powerful SGRB (a gamma-ray fluence an order of magnitude higher than GRB 180805A and/or a brighter X-ray counterpart), our MWA observations may be sensitive enough to detect coherent radio emission from the jet-ISM interaction and/or the magnetar remnant. Finally, we demonstrate that of all current low- frequency radio telescopes, only the MWA has the sensitivity and response times capable of probing prompt emission models associated with the initial SGRB merger event.
The Murchison Widefield Array (MWA) is an open access telescope dedicated to studying the low-frequency (80–300 MHz) southern sky. Since beginning operations in mid-2013, the MWA has opened a new observational window in the southern hemisphere enabling many science areas. The driving science objectives of the original design were to observe 21 cm radiation from the Epoch of Reionisation (EoR), explore the radio time domain, perform Galactic and extragalactic surveys, and monitor solar, heliospheric, and ionospheric phenomena. All together
programs recorded 20 000 h producing 146 papers to date. In 2016, the telescope underwent a major upgrade resulting in alternating compact and extended configurations. Other upgrades, including digital back-ends and a rapid-response triggering system, have been developed since the original array was commissioned. In this paper, we review the major results from the prior operation of the MWA and then discuss the new science paths enabled by the improved capabilities. We group these science opportunities by the four original science themes but also include ideas for directions outside these categories.
The warm, equable, and ice-free early Eocene Epoch permits investigation of ecosystem function and macro-ecological patterns during a very different climate regime than exists today. It also provides insight into what the future may entail, as anthropogenic CO2 release drives Earth toward a comparable hothouse condition. Studying plant–insect herbivore food webs during hothouse intervals is warranted, because these account for the majority of nonmicrobial terrestrial biodiversity. Here, we report new plant and insect herbivore damage census data from two floodplain sites in the Wind River Basin of central Wyoming, one in the Aycross Formation (50–48.25 Ma) at the basin edge (WRE) and the second in the Wind River Formation in the interior of the basin (WRI). The WRI site is in stratigraphic proximity to a volcanic ash that is newly dated to 52.416 ± 0.016/0.028/0.063 (2σ). We compare the Wind River Basin assemblages to published data from a 52.65 Ma floodplain flora in the neighboring Bighorn (BH) Basin and find that only 5.6% of plant taxa occur at all three sites and approximately 10% occur in both basins. The dissimilar floras support distinct suites of insect herbivores, as recorded by leaf damage. The relatively low-diversity BH flora has the highest diversity of insect damage, contrary to hypotheses that insect herbivore diversity tracks floral diversity. The distinctiveness of the WRE flora is likely due to its younger age and cooler reconstructed paleotemperature, but these factors are nearly identical for the WRI and BH floras. Site-specific microenvironmental factors that cannot be measured easily in deep time may account for these differences. Alternatively, the Owl Creek Mountains between the two basins may have provided a formidable barrier to the thermophilic organisms that inhabited the basin interiors, supporting Janzen's hypothesis that mountain passes appear higher in tropical environments.
For the first time, valence electron energy-loss spectroscopy (VEELS) was applied to individual single-crystalline SnO2 nanowires to investigate the dielectric function, band gap, and optical absorption coefficient. The results are compared with data from optical techniques such as spectroscopic ellipsometry and UV-Vis, and theoretical calculations from variations of density functional theory. The data obtained agree well with the standard optical and theoretical techniques. The dielectric function and optical absorption coefficient are given up to 20 eV, which otherwise requires a synchrotron source and large single crystals via optical methods. The energy loss function is given up to 40 eV, which gives a useful comparison to previous theoretical studies in an energy range that cannot be achieved via optical measurements. The comparison gives confidence in the accuracy of this method for exploring spatially-resolved measurements in individual nanoparticles or more complex nanostructures that are otherwise difficult to measure accurately using optical techniques.
In this article, we advance a generic theory of institutional change and illustrate it through a study of the Gas Deregulation Act of 1977–78. The passage of the Act provides an informative case study about institutional change as an innovative postcloture filibuster was implemented, and then defeated, in the course of the debate. Contrary to Shepsle’s argument that institutions determine outcomes, we argue that the legislative majority shaped the institution to get the policy outcome it wanted. We find evidence that negotiations among competing coalitions constrained outcomes to be inside the uncovered set. When the filibuster-related rules threatened to lead to an outcome outside of the uncovered set, the rules were changed to avoid this outcome. Our analysis calls into question both the view of majority rule as generically leading to chaos and the view that institutions are the essential tool to overcome such instability.
Background: A recommendation in original descriptions of motivational interviewing (MI) was to “explore ambivalence”. Contrasting procedures for doing so have been clarified through the evolution of MI. Aims: This article describes two conceptually distinct methods for responding to ambivalence: decisional balance (DB) and MI's evocation of change talk, and reviews empirical evidence to recommend when each procedure is appropriate (and inappropriate) in clinical practice. Method: The authors summarize findings of clinical outcome research to examine how these two interventions impact the resolution of client ambivalence. Results: With ambivalent people, a DB intervention tends to decrease commitment to change, whereas evocation (a key element of MI) promotes change. When a person has already made the decision to change, evocation is unnecessary and may deter change, whereas DB may further strengthen commitment. Conclusions: DB is an appropriate procedure when the clinician wishes to maintain neutrality and not favor the resolution of ambivalence in any particular direction. Evocation is appropriate when the clinician intends to help clients resolve ambivalence in the direction of change.
Objectives: The aim of this study was to develop a decision support tool to assess the potential benefits and costs of new healthcare interventions.
Methods: The Canadian Partnership Against Cancer (CPAC) commissioned the development of a Cancer Risk Management Model (CRMM)—a computer microsimulation model that simulates individual lives one at a time, from birth to death, taking account of Canadian demographic and labor force characteristics, risk factor exposures, and health histories. Information from all the simulated lives is combined to produce aggregate measures of health outcomes for the population or for particular subpopulations.
Results: The CRMM can project the population health and economic impacts of cancer control programs in Canada and the impacts of major risk factors, cancer prevention, and screening programs and new cancer treatments on population health and costs to the healthcare system. It estimates both the direct costs of medical care, as well as lost earnings and impacts on tax revenues. The lung and colorectal modules are available through the CPAC Web site (www.cancerview.ca/cancerrriskmanagement) to registered users where structured scenarios can be explored for their projected impacts. Advanced users will be able to specify new scenarios or change existing modules by varying input parameters or by accessing open source code. Model development is now being extended to cervical and breast cancers.