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The Square Kilometre Array (SKA) is a planned large radio interferometer designed to operate over a wide range of frequencies, and with an order of magnitude greater sensitivity and survey speed than any current radio telescope. The SKA will address many important topics in astronomy, ranging from planet formation to distant galaxies. However, in this work, we consider the perspective of the SKA as a facility for studying physics. We review four areas in which the SKA is expected to make major contributions to our understanding of fundamental physics: cosmic dawn and reionisation; gravity and gravitational radiation; cosmology and dark energy; and dark matter and astroparticle physics. These discussions demonstrate that the SKA will be a spectacular physics machine, which will provide many new breakthroughs and novel insights on matter, energy, and spacetime.
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.
Legionnaires’ disease (LD) is a globally distributed systemic infectious disease. The burden of LD in many regions is still unclear, especially in Asian countries including China. A survey of Legionella infection using real-time PCR and nested sequence-based typing (SBT) was performed in two hospitals in Shanghai, China. A total of 265 bronchoalveolar lavage fluid (BALF) specimens were collected from hospital A between January 2012 and December 2013, and 359 sputum specimens were collected from hospital B throughout 2012. A total of 71 specimens were positive for Legionella according to real-time PCR focusing on the 5S rRNA gene. Seventy of these specimens were identified as Legionella pneumophila as a result of real-time PCR amplification of the dotA gene. Results of nested SBT revealed high genetic polymorphism in these L. pneumophila and ST1 was the predominant sequence type. These data revealed that the burden of LD in China is much greater than that recognized previously, and real-time PCR may be a suitable monitoring technology for LD in large sample surveys in regions lacking the economic and technical resources to perform other methods, such as urinary antigen tests and culture methods.
We compiled a sample of 57 galaxies with spectroscopically confirmed redshifts and SPIRE detections in all three bands at z = 2.5-6.4, and compared their SPIRE colors with SED templates from local and high-z libraries. We find that local calibrations are inconsistent with high-z observations. For high-z libraries, the templates with an evolution from z = 0 to 3 can describe the average colors of the observations at high redshift well. Based on the templates, we defined color cuts to divide the SPIRE color-color diagram into different regions with different mean redshifts. We tested this method and two other color cut methods using a larger sample (783 galaxies) with photometric redshifts. We find that these color cuts can separate the sample into subsamples with different mean redshifts, but the dispersion of redshifts in each subsample is considerably large. Additional information is needed for better sampling.
Based on large-signal theory, a one-dimensional theoretical model of a coaxial vircator is developed to give the microwave gain of the nonlinear beam–wave interaction, and the effect of injected current premodulation on the microwave gain is analysed theoretically. In addition, a coaxial vircator with improved dual-cavity modulation structure, which has the advantage of enhancing the effect of the modulation cavity on the injected electron beam by way of feedback microwaves, is presented. The simulation results are presented to test the validity of the proposed theory, and it can be seen that the system power efficiency can become further strengthened by adjusting the parameters of the microwave feedback channel until the feedback electric field is at the proper phase. Finally, through optimization, a structure capable of generating 7.05 GW average output power and 19.5 % power conversion efficiency at 2.95 GHz operating frequency is obtained.
This study characterized Neisseria meningitidis serogroup C strains in China in order to establish their genetic relatedness and describe the use of multilocus variable-number tandem-repeat (VNTR) analysis (MLVA) to provide useful epidemiological information. A total of 215 N. meningitidis serogroup C strains, obtained from 2003 to 2012 in China, were characterized by MLVA with different published schemes as well as multilocus sequence typing. (i) Based on the MLVA scheme with a combination of five highly variable loci, 203 genotypes were identified; this level of discrimination supports its use for resolving closely related isolates. (ii) Based on a combination of ten low variable loci, clear phylogenetic relationships were established within sequence type complexes. In addition, there was evidence of microevolution of VNTR loci over the decade as strain lineages spread from Anhui to other provinces, the more distant the provinces from Anhui, the higher the genetic variation.
In a large serosurvey performed in Gaobeidian city, China, 1032 children and adolescents aged 3–18 years were divided into three age groups: 3–6, 7–11, and 12–18 years. The geometric mean of IgG antibodies against pertussis toxin (anti-PT IgG) varied from 3·47 IU/ml (3–6 years) to 8·71 IU/ml (12–18 years) and the seroprevalence (⩾40 IU/ml) varied from 4·48% (7–11 years) to 11·76% (12–18 years). Infections were clustered in three secondary schools (schools 1–3). However, excluding secondary schools 1–3, the IgG PT levels, seroprevalence and rates of recent infections (>100 IU/ml) in secondary schools 4–7 (where infections were not clustered) were very close to those in the 3–6 and 7–11 years age groups. This suggests that the high seroprevalence and anti-PT IgG levels in adolescents in Gaobeidian city, China were caused by the clustered cases in certain secondary schools. Our results also suggested that pertussis was still circulating in China, and the reported incidence might be underestimated.
The main Neisseria meningitidis adhesion molecules, type IV pili (Tfp) and Neisseria adhesion A (NadA), play important roles in the pathogenesis of invasive meningococcal disease. PilE is the major Tfp subunit. In this study, the prevalence and genetic diversity of pilE and nadA were investigated in the prevalent serogroups and clonal complexes (CC) of N. meningitidis isolated in China. All serogroup A strains belonging to CC1 and CC5 and all CC11 serogroup W135 strains were clustered into class II PilE clades. All serogroup C and most of serogroup B isolates except CC8 and ST5642 were class I PilE clades. Class II pilE sequences were highly conserved. All isolates belonging to class I PilE isolates were nadA negative. However, nadA-positive strains were exclusively found in CC5 and CC11 isolates (class II PilE). This study showed that PilE and NadA may be related to epidemic or endemic meningococcal disease.
Energetic divergent proton beams can be generated in the interaction of ultra-intense laser pulses with solid-density foil targets via target normal sheath acceleration (TNSA). In this paper, a scheme using a capillary to reduce the proton beam divergence is proposed. By two-dimensional particle-in-cell (PIC) simulations, it is shown that strong transverse electric and magnetic fields rapidly grow at the inner surface of the capillary when the laser-driven hot electrons propagate through the target and into the capillary. The spontaneous magnetic field collimates the electron flow, and the ions dragged from the capillary wall by hot electrons neutralize the negative charge and thus restrain the transverse extension of the sheath field set up by electrons. The proton beam divergence, which is mainly determined by the accelerating sheath field, is therefore reduced by the transverse limitation of the sheath field in the capillary.
Given the unpredictability of Neisseria meningitidis outbreaks and the increased prevalence of serogroup C strains following the introduction of serogroup A-based vaccines, we conducted an analysis of serogroups and sequence types (STs) in disease-associated and carrier N. meningitidis isolates that have emerged in China since 2003. We used multilocus sequence-typing techniques to investigate 371 N. meningitidis strains isolated from patients with meningitis and healthy carriers. Two lineages were identified in serogroup A and C isolates, genotyped as the ST5 complex and ST4821 complex, respectively. Both clonal complexes were found throughout China, although ST4821 was more concentrated in the eastern region of the country. The ST5 complex has been persistent in China since the late 1980s and has since spread across the entire country. Isolates belonging to the ST4821 complex have been a dominant lineage since 2003.
Studies in Western countries have repeatedly shown that women with a history of childhood sexual abuse (CSA) are at increased risk for developing major depression (MD). Would this relationship be found in China?
Three levels of CSA (non-genital, genital, and intercourse) were assessed by self-report in two groups of Han Chinese women: 1970 clinically ascertained with recurrent MD and 2597 matched controls. Diagnostic and other risk factor information was assessed at personal interview. Odds ratios (ORs) were calculated by logistic regression and regression coefficients by linear or Poisson regression.
Any form of CSA was significantly associated with recurrent MD [OR 3.26, 95% confidence interval (CI) 1.95–5.45]. This association strengthened with increasing CSA severity: non-genital (OR 2.47, 95% CI 1.17–5.23), genital (OR 2.77, 95% CI 1.32–5.83) and intercourse (OR 13.35, 95% CI 1.83–97.42). The association between any form of CSA and MD remained significant after accounting for parental history of depression, childhood emotional neglect (CEN), childhood physical abuse (CPA) and parent–child relationship. Among the depressed women, those with CSA had an earlier age of onset, longer depressive episodes and an increased risk for generalized anxiety disorder (GAD; OR 1.92, 95% CI 1.39–2.66) and dysthymia (OR 2.16, 95% CI 1.52–3.09).
In Chinese women CSA is strongly associated with MD and this association increases with greater severity of CSA. Depressed women with CSA have an earlier age of onset, longer depressive episodes and increased co-morbidity with GAD and dysthymia. Although reporting biases cannot be ruled out, our results are consistent with the hypothesis that, as in Western countries, CSA substantially increases the risk for MD in China.
An outbreak of rabies affected domestic raccoon dogs on an animal farm in Inner Mongolia, China in 2007. A study was conducted to characterize the aetiological agent and clarify the origin of the rabies virus. Brain tissues were obtained from five rabid raccoon dogs. Viral nucleoprotein antigen was detected in the brain tissues and five rabies viruses were isolated from these rabid animals. Phylogenetic analysis of the N and G gene sequences showed that these isolates were closely related to Arctic-like rabies viruses isolated from the far-eastern region of Russia and South Korea, but distinct from the rabies viruses that are widely distributed in endemic areas in China. Epidemiological data suggested that the likely source of infection was from one wild raccoon dog that was captured and placed in the same type of pen used for domestic raccoon dogs.
This work developed a metal-reinforced ceramic membrane processing approach [by using perovskite La0.2Sr0.8 CoO3-x (LSCO-80) as the model membrane] with the aim of overcoming the membrane-cracking problem. A thin layer of Ag/Pd alloy was incorporated into the LSCO-80 membrane made by dip coating and sintering. It is not viable to obtain a Pd/Ag alloy film using the co-plating method because Ag+ ion strongly inhibits chemical reduction of Pd2+ ion, and the alkaline plating bath causes severe etching of LSCO-80. This obstacle was circumvented through a layer-by-layer deposition procedure, in which Ag and Pd layers were deposited subsequently onto LSCO membrane. The Ag and Pd layers undergo alloying when the laminar structure was subjected to calcinations at 1000°C. It was found that the Pd/Ag alloy drifts beneath into pores in the LSCO layer. The resultant metal-ceramic composite membrane shows excellent structural integrity and free of micro-cracks.
Nanometer-size gadolinium powders (nm-Gd) have been prepared by means of evaporation condensation of Gd atoms within inert gas atmosphere. Microscopic analyses, based on measurements of small angle x-ray scattering (SAXS), x-ray diffraction (XRD), Raman scattering spectrum (RSS), and observation with transmission electron microscope (TEM), have been carried out in order to evaluate the size and size distribution of the as-prepared nm-Gd powder. It turns out that the size distribution function of nm-Gd powder agrees very well with the distribution function of Rayleigh instead of logarithmic distribution. The mean size d of nm-Gd powders bears a linear relationship with the logarithm of the pressure p of the inert gas atmosphere as follows: d = a + b · ln p. A discussion concerning the influence of particle size of nm-Gd powder on nanostructured material parameters such as the size distribution, specific surface area, and the percentage of interface atoms have been given in detail.