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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.
An outbreak of acute hepatitis recently occurred in a nursing home in Zhejiang Province, China. The objectives of this study were to confirm the outbreak and identify the aetiology, source and transmission patterns. All residents and staff in or near the nursing home during the period from 1 October 2014 to 21 May 2015 were investigated regarding hygiene and for epidemiological information including water and food (eating meat especially pork products). Serum and stool specimens were collected for detection of hepatitis E virus (HEV) antibodies using ELISA and RNA using RT–PCR. Samples that were RNA positive were genotyped. Of 185 senior residents and 24 staff in the nursing home, there were 37 laboratory-confirmed cases during the outbreak. Of these cases, 12 patients (three deaths) were symptomatic with jaundice, a common clinical symptom for hepatitis E infection. HEV strains were isolated from three cases and they formed a single cluster within genotype 4d. A case-control study was conducted to investigate potential risk factors for the outbreak and the results revealed that cases more often washed their dishes and rinsed their mouths using tap water than the controls (P < 0·05). Based on hygiene investigation and meteorological information, it is likely that HEV-infected sewage and faeces contaminated the water network on rainy days. Collectively, these results suggest that the outbreak of HEV genotype 4 infection was most likely caused by contaminated tap water rather than food.
The Sun drives most events of space weather in the vicinity of the Earth. Because the activities of the Sun are complicated, a visualized chart with key objects of solar activities is needed for space weather forecast. This work investigates the key objects in research during the past forty years and surveys a variety of solar observational data. We design the solar synoptic chart (SSC) that covers the key objects of solar activities, i.e., active regions, coronal holes, filaments/prominences, flares and coronal mass ejections, and synthesizes images from different heights and temperatures of solar atmosphere. The SSC is used to analyze the condition of the Sun in March 2012 and October 2014 as examples. The result shows that the SSC is timely, comprehensive, concise and easy to understand. It has the potentiality for space weather forecast and can help in improving the public education.
How large, 100-AU scale, rotationally supported disks form around protostars remains unsettled, both observationally and theoretically. In this contribution, we discuss the theoretical difficulties with disk formation in the presence of a dynamically significant magnetic field and their possible resolutions. These difficulties are caused by the concentration of magnetic field lines close to the forming star by protostellar collapse, and the strong magnetic braking associated with the concentrated field. Possible resolutions include magnetic field-rotation axis misalignment, non-ideal MHD effects, and turbulence. The field-rotation misalignment has been shown to promote disk formation, especially when the field is relatively weak and the misalignment angle is relatively large. Non-ideal MHD effects can enable the formation of small disks at early times. How such disks grow at later times remains to be fully quantified. Turbulence has been found to enable disk formation in a number of simulations, but the exact reason for its beneficial effect is debated.
Post-flare loops (PFLs) usually appear in the late phase of eruptive flares as an arcade-like loop system. The Atmospheric Imaging Assembly (AIA) on-board the Solar Dynamics Observatory (SDO) delivers continuously high temporal and spatial resolution extreme ultraviolet (EUV) observations, providing a unique chance to study the PFLs. In this work, we use SDO/AIA high-quality EUV images to study the dark loop-like features in post-flare loops (DPFLs) of an X5.4 flare. Our analysis shows that: 1) the DPFLs are darker than their surrounding and the bright loops, but are brighter than the EUV background; 2) the DPFLs appear in multiple EUV channels, which indicates that they are absorption features; 3) the DPFLs are associated with downflows that are caused by the thermal instability in the cooling process of the flare.
No published studies have discussed details of the prognosis and survival of patients with severe avian influenza A(H7N9) infection. In this study we analysed 128 laboratory-confirmed cases of severe H7N9 infection in Zhejiang province, the most affected region during the H7N9 epidemic in mainland China. We found that an increase in patient age by 5 years was associated with a 1·41 [95% confidence interval (CI) 1·19–1·67] times odds ratio for fatality. In addition, the time interval between the first clinical visit after symptom onset and hospital admission was inversely associated with survival time since admission. Of the 47 patients who died of the disease, when the time interval between the first clinical visit and hospital admission increased by 1 day, the duration of survival was 0·78 times (95% CI 0·62–0·98) as long. Our results suggest that patients with severe influenza H7N9 infection at older ages were at a higher risk of fatality, and that a delay in hospital admission was associated with more rapid death. More studies are required to corroborate our major findings.
We compared the epidemiological and clinical features of avian influenza A(H7N9) virus infections in the population in Zhejiang province, China, between March and April 2013 (first wave) and October 2013 and February 2014 (second wave). No statistical difference was found for age, sex, occupation, presence of underlying conditions, exposure history, white blood cell count, lymphocyte percentage and illness timeline and duration (all P > 0·05). The virus spread to 30 new counties compared to the first wave. The case-fatality rate was 22% in the first wave and 42% in the second (P = 0·023). Of those infected, 66% in the first wave and 62% in the second wave had underlying conditions. The proportion of those exposed to live poultry markets were 80% and 66%, respectively. We recommend permanent closure of live poultry markets and reformation of poultry supply and sales.
The THz spectral region includes a number of important transitions which
allow us to trace the evolution of the interstellar medium. Because of the
opacity of the atmosphere in this spectral range, the best sites for
ground-based THz observations are on the Antarctic Plateau; of these sites,
Dome A is expected to be the best. THz survey science can be carried out
with small telescopes, easing logistical constraints. By deploying a
submillimetre-wave tipper/ telescope to Dome A, we have trialled several
technologies for such an instrument, and we are able to test whether the
site quality is sufficient for THz surveys.
Single-walled carbon nanotubes can be used as electron sources in the
process of field emission, and have great potential for practical
application of the field emission display (FED) panels with large screen
size. We fabricated a FED using the single-walled carbon nanotubes (SWNTs)
as the cathode by the screen-printing process. Test showed that the SWNTs
emitters exhibit excellent macroscopic emission properties. It has low
turn-on voltage (2.7 V/μm) and high brightness, with a high current
density of good uniformity and stability. It was observed that the field
emission qualitatively follows the conventional Fowler–Nordheim (F–N)
theory, and aging treatment played an important role in improving the image
uniformity and stability. Compared to other complicated processes, the
simple fabrication using screen-printing process seems to be advantageous
for practical application.
The velocity fluctuations of particles in a low-Reynolds-number fluidized bed have important similarities and differences with the velocity fluctuations in a low-Reynolds-number sedimenting suspension. We show that, like sedimentation, the velocity fluctuations in a fluidized bed are described well by the balance between density fluctuations due to Poisson statistics and Stokes drag. However, unlike sedimentation, the correlation length of the fluctuations in a fluidized bed increases with volume fraction. We argue that this difference arises because the relaxation time of density fluctuations is completely different in the two systems.
We present a new process based on the electrolysis of glass, which allows the transfer of a single-crystal silicon film while creating an in situ barrier layer free of mobile ions in the glass. This barrier layer consists only of network-forming elements (i.e., aluminum, silicon, and boron) and is free of modifiers. The barrier layer glass is unusual and cannot be synthesized via any of the known glass-forming processes. The barrier layer is thermally stable and thus allows the fabrication of displays with ultimate performance. The process consists of the hydrogen ion implantation of silicon to create a defect structure followed by bringing the glass and the silicon wafer in contact, and finally applying electrical potential to cause the electrolysis of glass.
It is well established that the response of devices based on the
giant magnetoresistance (GMR) effect depends critically on film
microstructure, with parameters such as interfacial abruptness, the
roughness and waviness of the layers, and grain size being crucial.
Such devices have applications in information storage systems, and are
therefore of great technological interest as well as being of
fundamental scientific interest. The layers must be studied at high
spatial resolution if the microstructural parameters are to be
characterized with sufficient detail to enable the effects of
fabrication conditions on properties to be understood, and the
techniques of high resolution electron microscopy, transmission
electron microscopy chemical mapping, and atom probe microanalysis are
ideally suited. This article describes the application of these
techniques to a range of materials including spin valves, spin tunnel
junctions, and GMR multilayers.
We present a model for velocity fluctuations of dilute sedimenting spheres at low Reynolds number. The central idea is that a vertical stratification causes the fluctuations to decrease below those of an independent uniform distribution of particles, such a stratification naturally occurring from the broadening of the sedimentation front. We use numerical simulations, scaling arguments, structure factor calculations, and experiments to show that there is a critical stratification above which the characteristics of the density and velocity fluctuations change significantly. For thin cells, the broadening of the sediment front (and the resulting stratification) is small, so the velocity fluctuations are predicted by independent-Poisson-distribution estimates. In very thick cells, the stratification is significant, leading to persistent decay of the velocity fluctuations for the duration of the experiment. Estimated stratifications quantitatively agree with the simulations, and indicate the likelihood that previous experimental measurements were also affected by stratification. The velocity fluctuations in sedimentation are therefore not universal but instead depend on both the cell shape and developing stratification.
We present an inexpensive, bulk-processing technique for the mass fabrication of a high-performance, nanocrystalline intermetallic with no internal flaws: the recrystallization of plastically deformed ingots through controlled heat treatments. We demonstrate that FeCo alloys with average grain sizes of 100 nm can be produced using this method. The nanocrystalline materials have tensile yield strengths as high as 2.2 GPa and have plastic tensile ductilities over 1.3%. Such superior properties at room temperature are currently unattainable when nanocrystalline materials are prepared by other methods.
Microchemistry and mechanical properties of a copper/tin–bismuth Pb-free solder interconnect were examined in the as-reflowed and aged conditions by in situ Auger fracture and interface fracture mechanics techniques. In the as-reflowed condition, the solder–copper interface was highly resistant to fracture, and the fracture mechanism was ductile with the crack path following the interface between the solder alloy and the copper–tin intermetallic phase. Upon thermal aging, bismuth segregation was found to occur on the copper–intermetallic interface. Auger depth profiling indicated that the segregation was confined to about one monolayer from the interface. The segregation was shown to embrittle the interface, resulting in an approximately 5-fold decrease in the interfacial fracture resistance.
The topological theory of interfacial defects and the associated flux analysis are reviewed. It is shown that the shears and diffusive fluxes associated with the motion of disconnections can be determined directly from their crystallographic characteristics, and that the effects of changes in chemical composition, interfacial misfit and ordering can be incorporated into the analysis. The special conditions are identified for which there is conservation of atomic sites during the motion of disconnections. It is shown that, under these circumstances, disconnection motion may result in mixed-mode displacive-diffusive transformations whereby diffusion is required for the transformation to proceed but the interfaces exhibit crystallographic characteristics which one would normally associate with a martensitic transformation. It is shown that the growth of γ lamellae in TiAl-based alloys is an example of such a mixed-mode transformation.
Scanning Transmission Electron Microscope (STEM) Energy Dispersive X-Ray analysis (EDX) linescans and mapping have been used to examine the large angle grain boundary chemistry of Ni-rich Ni3AI both with and without boron. The results show that the Al content is reduced while the Ni content is unchanged at the grain boundaries in all these alloys, with the percentage of reduction of Al at the grain boundaries decreasing as boron concentration increases. This is ascribed to differential surface sputtering of the lighter Al atoms.