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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 Murchison Widefield Array (MWA) is an electronically steered low-frequency (<300 MHz) radio interferometer, with a ‘slew’ time less than 8 s. Low-frequency (∼100 MHz) radio telescopes are ideally suited for rapid response follow-up of transients due to their large field of view, the inverted spectrum of coherent emission, and the fact that the dispersion delay between a 1 GHz and 100 MHz pulse is on the order of 1–10 min for dispersion measures of 100–2000 pc/cm3. The MWA has previously been used to provide fast follow-up for transient events including gamma-ray bursts (GRBs), fast radio bursts (FRBs), and gravitational waves, using systems that respond to gamma-ray coordinates network packet-based notifications. We describe a system for automatically triggering MWA observations of such events, based on Virtual Observatory Event standard triggers, which is more flexible, capable, and accurate than previous systems. The system can respond to external multi-messenger triggers, which makes it well-suited to searching for prompt coherent radio emission from GRBs, the study of FRBs and gravitational waves, single pulse studies of pulsars, and rapid follow-up of high-energy superflares from flare stars. The new triggering system has the capability to trigger observations in both the regular correlator mode (limited to ≥0.5 s integrations) and using the Voltage Capture System (VCS, 0.1 ms integration) of the MWA and represents a new mode of operation for the MWA. The upgraded standard correlator triggering capability has been in use since MWA observing semester 2018B (July–Dec 2018), and the VCS and buffered mode triggers will become available for observing in a future semester.
Enhancing the supply of arginine (Arg), a semi-essential amino acid, has positive effects on immune function in dairy cattle experiencing metabolic stress during early lactation. Our objective was to determine the effects of Arg supplementation on biomarkers of liver damage and inflammation in cows during early lactation. Six Chinese Holstein lactating cows with similar BW (508 ± 14 kg), body condition score (3.0), parity (4.0 ± 0), milk yield (30.6 ± 1.8 kg) and days in milk (20 ± days) were randomly assigned to three treatments in a replicated 3 × 3 Latin square design balanced for carryover effects. Each period was 21 days with 7 days for infusion and 14 days for washout. Treatments were (1) Control: saline; (2) Arg group: saline + 0.216 mol/day l-Arg; and (3) Alanine (Ala) group: saline + 0.868 mol/day l-Ala (iso-nitrogenous to the Arg group). Blood and milk samples from the experimental cows were collected on the last day of each infusion period and analyzed for indices of liver damage and inflammation, and the count and composition of somatic cells in milk. Compared with the Control, the infusion of Arg led to greater concentrations of total protein, immunoglobulin M and high density lipoprotein cholesterol coupled with lower concentrations of haptoglobin and tumor necrosis factor-α, and activity of aspartate aminotransferase in serum. Infusion of Ala had no effect on those biomarkers compared with the Control. Although milk somatic cell count was not affected, the concentration of granulocytes was lower in response to Arg infusion compared with the Control or Ala group. Overall, the biomarker analyses indicated that the supplementation of Arg via the jugular vein during early lactation alleviated inflammation and metabolic stress.
A compact transition between conductor-backed coplanar waveguide (CBCPW) and substrate integrated suspended line (SISL) is presented. Compared to the reported transitions from CBCPW to SISL, performance and compactness are improved. For demonstration purpose, a multilayer transition is designed and fabricated for operation up to 46 GHz. Experimental results, based on an electronic calibration and thru–reflect–line calibration allowing measurement in the 0.01–50 GHz frequency range, demonstrate an insertion loss of 0.59 ± 0.51 dB with a return loss of better than 10 dB in the 10 MHz to 46 GHz frequency range.
We apply two methods to estimate the 21-cm bispectrum from data taken within the Epoch of Reionisation (EoR) project of the Murchison Widefield Array (MWA). Using data acquired with the Phase II compact array allows a direct bispectrum estimate to be undertaken on the multiple redundantly spaced triangles of antenna tiles, as well as an estimate based on data gridded to the uv-plane. The direct and gridded bispectrum estimators are applied to 21 h of high-band (167–197 MHz; z = 6.2–7.5) data from the 2016 and 2017 observing seasons. Analytic predictions for the bispectrum bias and variance for point-source foregrounds are derived. We compare the output of these approaches, the foreground contribution to the signal, and future prospects for measuring the bispectra with redundant and non-redundant arrays. We find that some triangle configurations yield bispectrum estimates that are consistent with the expected noise level after 10 h, while equilateral configurations are strongly foreground-dominated. Careful choice of triangle configurations may be made to reduce foreground bias that hinders power spectrum estimators, and the 21-cm bispectrum may be accessible in less time than the 21-cm power spectrum for some wave modes, with detections in hundreds of hours.
Agents that block the renin–angiotensin system (RAS) improve glucoregulation in the metabolic syndrome disorder. We evaluated the effects of egg white hydrolysate (EWH), previously shown to modulate the protein abundance of RAS component in vivo, on glucose homeostasis in diet-induced insulin-resistant rats. Sprague–Dawley rats were fed a high-fat diet (HFD) for 6 weeks to induce insulin resistance. They were then randomly divided into four groups receiving HFD or HFD supplemented with different concentrations of EWH (1, 2 and 4 %) for another 6 weeks in the first trial. In the second trial, insulin-resistant rats were divided into two groups receiving only HFD or HFD+4 % EWH for 6 weeks. Glucose homeostasis was assessed by oral glucose tolerance and insulin tolerance tests. Insulin signalling and protein abundance of RAS components, gluconeogenesis enzymes and PPARγ were evaluated in muscle, fat and liver. Adipocyte morphology and inflammatory markers were evaluated. In vivo administration of EWH increased insulin sensitivity, improved oral glucose tolerance (P < 0·0001) and reduced systemic inflammation (P < 0·05). EWH potentiated insulin-induced Akt phosphorylation in muscle (P = 0·0341) and adipose tissue (P = 0·0276), but minimal differences in the protein abundance of tissue RAS components between the EWH and control groups were observed. EWH treatment also reduced adipocyte size (P = 0·0383) and increased PPARγ2 protein abundance (P = 0·0237). EWH treatment yielded positive effects on the inflammatory profile, glucose tolerance, insulin sensitivity and adipocyte differentiation in HFD-induced insulin resistance rats. The involvement of local RAS activity requires further investigation.
We provide the first in situ measurements of antenna element beam shapes of the Murchison Widefield Array. Most current processing pipelines use an assumed beam shape, which can cause absolute and relative flux density errors and polarisation ‘leakage’. Understanding the primary beam is then of paramount importance, especially for sensitive experiments such as a measurement of the 21-cm line from the epoch of reionisation, where the calibration requirements are so extreme that tile to tile beam variations may affect our ability to make a detection. Measuring the primary beam shape from visibilities is challenging, as multiple instrumental, atmospheric, and astrophysical factors contribute to uncertainties in the data. Building on the methods of Neben et al. [Radio Sci., 50, 614], we tap directly into the receiving elements of the telescope before any digitisation or correlation of the signal. Using ORBCOMM satellite passes we are able to produce all-sky maps for four separate tiles in the XX polarisation. We find good agreement with the beam model of Sokolowski et al. [2017, PASA, 34, e062], and clearly observe the effects of a missing dipole from a tile in one of our beam maps. We end by motivating and outlining additional on-site experiments.
We describe the motivation and design details of the ‘Phase II’ upgrade of the Murchison Widefield Array radio telescope. The expansion doubles to 256 the number of antenna tiles deployed in the array. The new antenna tiles enhance the capabilities of the Murchison Widefield Array in several key science areas. Seventy-two of the new tiles are deployed in a regular configuration near the existing array core. These new tiles enhance the surface brightness sensitivity of the array and will improve the ability of the Murchison Widefield Array to estimate the slope of the Epoch of Reionisation power spectrum by a factor of ∼3.5. The remaining 56 tiles are deployed on long baselines, doubling the maximum baseline of the array and improving the array u, v coverage. The improved imaging capabilities will provide an order of magnitude improvement in the noise floor of Murchison Widefield Array continuum images. The upgrade retains all of the features that have underpinned the Murchison Widefield Array’s success (large field of view, snapshot image quality, and pointing agility) and boosts the scientific potential with enhanced imaging capabilities and by enabling new calibration strategies.
Cultivated pastures in southern China are being used to improve forage productivity and animal performance, but studies on grazing behaviour of goats in these cultivated pastures are still rare. In the current study, the grazing behaviour of Yunling black goats under low (5 goats/ha) and high (15 goats/ha) stocking rates (SRs) was evaluated. Data showed that the proportion of time goats spent on activities was: eating (0.59–0.87), ruminating (0.05–0.35), walking (0.03–0.06) and resting (0.01–0.03). Compared with low SR, goats spent more time eating and walking, and less time ruminating and resting under high SR. Goats had similar diet preferences under both SR and preferred to eat grasses (ryegrass and cocksfoot) more than a legume (white clover). The distribution of eating time on each forage species was more uniform under high v. low SR. Bites/step, bite weight and daily intake were greater under low than high SR. Results suggest that the SR affects grazing behaviour of goats on cultivated pasture, and identifying an optimal SR is critical for increasing bite weight and intake.
During emerging disease outbreaks, public health, emergency management officials and decision-makers increasingly rely on epidemiological models to forecast outbreak progression and determine the best response to health crisis needs. Outbreak response strategies derived from such modelling may include pharmaceutical distribution, immunisation campaigns, social distancing, prophylactic pharmaceuticals, medical care, bed surge, security and other requirements. Infectious disease modelling estimates are unavoidably subject to multiple interpretations, and full understanding of a model's limitations may be lost when provided from the disease modeller to public health practitioner to government policymaker. We review epidemiological models created for diseases which are of greatest concern for public health protection. Such diseases, whether transmitted from person-to-person (Ebola, influenza, smallpox), via direct exposure (anthrax), or food and waterborne exposure (cholera, typhoid) may cause severe illness and death in a large population. We examine disease-specific models to determine best practices characterising infectious disease outbreaks and facilitating emergency response and implementation of public health policy and disease control measures.
For livestock production systems to play a positive role in global food security, the balance between their benefits and disbenefits to society must be appropriately managed. Based on the evidence provided by field-scale randomised controlled trials around the world, this debate has traditionally centred on the concept of economic-environmental trade-offs, of which existence is theoretically assured when resource allocation is perfect on the farm. Recent research conducted on commercial farms indicates, however, that the economic-environmental nexus is not nearly as straightforward in the real world, with environmental performances of enterprises often positively correlated with their economic profitability. Using high-resolution primary data from the North Wyke Farm Platform, an intensively instrumented farm-scale ruminant research facility located in southwest United Kingdom, this paper proposes a novel, information-driven approach to carry out comprehensive assessments of economic-environmental trade-offs inherent within pasture-based cattle and sheep production systems. The results of a data-mining exercise suggest that a potentially systematic interaction exists between ‘soil health’, ecological surroundings and livestock grazing, whereby a higher level of soil organic carbon (SOC) stock is associated with a better animal performance and less nutrient losses into watercourses, and a higher stocking density with greater botanical diversity and elevated SOC. We contend that a combination of farming system-wide trials and environmental instrumentation provides an ideal setting for enrolling scientifically sound and biologically informative metrics for agricultural sustainability, through which agricultural producers could obtain guidance to manage soils, water, pasture and livestock in an economically and environmentally acceptable manner. Priority areas for future farm-scale research to ensure long-term sustainability are also discussed.
The discovery of the first electromagnetic counterpart to a gravitational wave signal has generated follow-up observations by over 50 facilities world-wide, ushering in the new era of multi-messenger astronomy. In this paper, we present follow-up observations of the gravitational wave event GW170817 and its electromagnetic counterpart SSS17a/DLT17ck (IAU label AT2017gfo) by 14 Australian telescopes and partner observatories as part of Australian-based and Australian-led research programs. We report early- to late-time multi-wavelength observations, including optical imaging and spectroscopy, mid-infrared imaging, radio imaging, and searches for fast radio bursts. Our optical spectra reveal that the transient source emission cooled from approximately 6 400 K to 2 100 K over a 7-d period and produced no significant optical emission lines. The spectral profiles, cooling rate, and photometric light curves are consistent with the expected outburst and subsequent processes of a binary neutron star merger. Star formation in the host galaxy probably ceased at least a Gyr ago, although there is evidence for a galaxy merger. Binary pulsars with short (100 Myr) decay times are therefore unlikely progenitors, but pulsars like PSR B1534+12 with its 2.7 Gyr coalescence time could produce such a merger. The displacement (~2.2 kpc) of the binary star system from the centre of the main galaxy is not unusual for stars in the host galaxy or stars originating in the merging galaxy, and therefore any constraints on the kick velocity imparted to the progenitor are poor.
This paper presents a numerical model for accurately representing the behaviors of lead-rubber bearings during earthquakes. This model, which is implemented in OpenSees as a user-defined element, accounts for the mechanical characteristics of bearings as follows: firstly, the bi-lateral interaction effect of hysteretic behaviors, as well as the variation in horizontal stiffness due to vertical load, is considered; secondly, the reduced vertical stiffness under large lateral displacement is incorporated by the piecewise linear formulation, and the linear reduction method is employed to determine the stability limit of bearings in the deformed configuration; furthermore, the cavitation and permanent damage effects in bearings are mathematically included. To validate the numerical model, simulation analyses are performed for a series of static and dynamic loading tests, and the numerical results show reasonable agreement with experimental ones, which indicates that the proposed model provides an effective tool for the failure mode analyses of bearings and the dynamic analyses of seismic isolated structures.
The physical processes driving the chemical evolution of galaxies in the last ~ 11Gyr cannot be understood without directly probing the dust-obscured phase of star-forming galaxies and active galactic nuclei. This phase, hidden to optical tracers, represents the bulk of the star formation and black hole accretion activity in galaxies at 1 < z < 3. Spectroscopic observations with a cryogenic infrared observatory like SPICA, will be sensitive enough to peer through the dust-obscured regions of galaxies and access the rest-frame mid- to far-infrared range in galaxies at high-z. This wavelength range contains a unique suite of spectral lines and dust features that serve as proxies for the abundances of heavy elements and the dust composition, providing tracers with a feeble response to both extinction and temperature. In this work, we investigate how SPICA observations could be exploited to understand key aspects in the chemical evolution of galaxies: the assembly of nearby galaxies based on the spatial distribution of heavy element abundances, the global content of metals in galaxies reaching the knee of the luminosity function up to z ~ 3, and the dust composition of galaxies at high-z. Possible synergies with facilities available in the late 2020s are also discussed.
We describe the design and performance of the Engineering Development Array, which is a low-frequency radio telescope comprising 256 dual-polarisation dipole antennas working as a phased array. The Engineering Development Array was conceived of, developed, and deployed in just 18 months via re-use of Square Kilometre Array precursor technology and expertise, specifically from the Murchison Widefield Array radio telescope. Using drift scans and a model for the sky brightness temperature at low frequencies, we have derived the Engineering Development Array’s receiver temperature as a function of frequency. The Engineering Development Array is shown to be sky-noise limited over most of the frequency range measured between 60 and 240 MHz. By using the Engineering Development Array in interferometric mode with the Murchison Widefield Array, we used calibrated visibilities to measure the absolute sensitivity of the array. The measured array sensitivity matches very well with a model based on the array layout and measured receiver temperature. The results demonstrate the practicality and feasibility of using Murchison Widefield Array-style precursor technology for Square Kilometre Array-scale stations. The modular architecture of the Engineering Development Array allows upgrades to the array to be rolled out in a staged approach. Future improvements to the Engineering Development Array include replacing the second stage beamformer with a fully digital system, and to transition to using RF-over-fibre for the signal output from first stage beamformers.