Topological Dirac and Weyl semimetals not only host quasiparticles analogous to the elementary fermionic particles in high-energy physics, but also have a non-trivial band topology manifested by ...gapless surface states, which induce exotic surface Fermi arcs1,2. Recent advances suggest new types of topological semimetal, in which spatial symmetries protect gapless electronic excitations without high-energy analogues3–11. Here, using angle-resolved photoemission spectroscopy, we observe triply degenerate nodal points near the Fermi level of tungsten carbide with space group \P\bar{6}m2\ (no. 187), in which the low-energy quasiparticles are described as three-component fermions distinct from Dirac and Weyl fermions. We further observe topological surface states, whose constant-energy contours constitute pairs of ‘Fermi arcs’ connecting to the surface projections of the triply degenerate nodal points, proving the non-trivial topology of the newly identified semimetal state.
Ferroelectric materials have a spontaneous electric polarization that can be manipulated for applications. The polarization is usually not uniform throughout the material, and for nanosized ...ferroelectrics, polarization can be quite complex. Using scanning transmission electron microscopy, Tang et al. found that in thin films of the ferroelectric PbTiO3, the polarization vector rotated in space, forming a closed loop, the so-called flux closure. The flux closure structures formed an array, with the period dependent on the width of the thin film, and caused the buildup of considerable strain within the crystal lattice of the material Science, this issue p. 547 Nanoscale ferroelectrics are expected to exhibit various exotic domain configurations, such as the full flux-closure pattern that is well known in ferromagnetic materials. Here we observe not only the atomic morphology of the flux-closure quadrant but also a periodic array of flux closures in ferroelectric PbTiO3 films, mediated by tensile strain on a GdScO3 substrate. Using aberration-corrected scanning transmission electron microscopy, we directly visualize an alternating array of clockwise and counterclockwise flux closures, whose periodicity depends on the PbTiO3 film thickness. In the vicinity of the core, the strain is sufficient to rupture the lattice, with strain gradients up to 109 per meter. Engineering strain at the nanoscale may facilitate the development of nanoscale ferroelectric devices.
Two-dimensional (2D) materials have been studied extensively as monolayers, vertical or lateral heterostructures. To achieve functionalization, monolayers are often patterned using soft lithography ...and selectively decorated with molecules. Here we demonstrate the growth of a family of 2D materials that are intrinsically patterned. We demonstrate that a monolayer of PtSe
can be grown on a Pt substrate in the form of a triangular pattern of alternating 1T and 1H phases. Moreover, we show that, in a monolayer of CuSe grown on a Cu substrate, strain relaxation leads to periodic patterns of triangular nanopores with uniform size. Adsorption of different species at preferred pattern sites is also achieved, demonstrating that these materials can serve as templates for selective self-assembly of molecules or nanoclusters, as well as for the functionalization of the same substrate with two different species.
The event rate, energy distribution and time-domain behaviour of repeating fast radio bursts (FRBs) contain essential information regarding their physical nature and central engine, which are as yet ...unknown
. As the first precisely localized source, FRB 121102 (refs.
) has been extensively observed and shows non-Poisson clustering of bursts over time and a power-law energy distribution
. However, the extent of the energy distribution towards the fainter end was not known. Here we report the detection of 1,652 independent bursts with a peak burst rate of 122 h
, in 59.5 hours spanning 47 days. A peak in the isotropic equivalent energy distribution is found to be approximately 4.8 × 10
erg at 1.25 GHz, below which the detection of bursts is suppressed. The burst energy distribution is bimodal, and well characterized by a combination of a log-normal function and a generalized Cauchy function. The large number of bursts in hour-long spans allows sensitive periodicity searches between 1 ms and 1,000 s. The non-detection of any periodicity or quasi-periodicity poses challenges for models involving a single rotating compact object. The high burst rate also implies that FRBs must be generated with a high radiative efficiency, disfavouring emission mechanisms with large energy requirements or contrived triggering conditions.
Dysbiotic oral microbiota has been associated with multiple sclerosis. However, the role and mechanism of oral microbiota in the development of multiple sclerosis are still elusive. Here, we ...demonstrated that ligature-induced periodontitis (LIP) aggravated experimental autoimmune encephalomyelitis (EAE) in mice, and this was likely dependent on the expansion of T helper 17 (Th17) cells. LIP increased the splenic richness of Enterobacter sp., which was able to induce the expansion of splenic Th17 cells and aggravate EAE in mice. LIP also led to enrichment of Erysipelotrichaceae sp. in the gut and increased Th17 cells in the large intestinal lamina propria of EAE mice. Fecal microbiota transplantation from EAE mice with LIP also promoted EAE symptoms. In conclusion, periodontitis exacerbates EAE, likely through ectopic colonization of oral pathobionts and expansion of Th17 cells.
Although elastic strains, particularly inhomogeneous strains, are able to tune, enhance or create novel properties of some nanoscale functional materials, potential devices dominated by inhomogeneous ...strains have not been achieved so far. Here we report a fabrication of inhomogeneous strains with a linear gradient as giant as 10
per metre, featuring an extremely lower elastic energy cost compared with a uniformly strained state. The present strain gradient, resulting from the disclinations in the BiFeO
nanostructures array grown on LaAlO
substrates via a high deposition flux, induces a polarization of several microcoulomb per square centimetre. It leads to a large built-in electric field of several megavoltage per metre, and gives rise to a large enhancement of solar absorption. Our results indicate that it is possible to build up large-scale strain-dominated nanostructures with exotic properties, which in turn could be useful in the development of novel devices for electromechanical and photoelectric applications.
The super τ-charm facility (STCF) is an electron−positron collider proposed by the Chinese particle physics community. It is designed to operate in a center-of-mass energy range from 2 to 7 GeV with ...a peak luminosity of 0.5 × 10 35 cm −2·s −1 or higher. The STCF will produce a data sample about a factor of 100 larger than that of the present τ-charm factory - the BEPCII, providing a unique platform for exploring the asymmetry of matter-antimatter (charge-parity violation), in-depth studies of the internal structure of hadrons and the nature of non-perturbative strong interactions, as well as searching for exotic hadrons and physics beyond the Standard Model. The STCF project in China is under development with an extensive R&D program. This document presents the physics opportunities at the STCF, describes conceptual designs of the STCF detector system, and discusses future plans for detector R&D and physics case studies.
A topological meron features a non-coplanar structure, whose order parameters in the core region are perpendicular to those near the perimeter. A meron is half of a skyrmion, and both have potential ...applications for information carrying and storage. Although merons and skyrmions in ferromagnetic materials can be readily obtained via inter-spin interactions, their behaviour and even existence in ferroelectric materials are still elusive. Here we observe using electron microscopy not only the atomic morphology of merons with a topological charge of 1/2, but also a periodic meron lattice in ultrathin PbTiO
films under tensile epitaxial strain on a SmScO
substrate. Phase-field simulations rationalize the formation of merons for which an epitaxial strain, as a single alterable parameter, plays a critical role in the coupling of lattice and charge. This study suggests that by engineering strain at the nanoscale it should be possible to fabricate topological polar textures, which in turn could facilitate the development of nanoscale ferroelectric devices.
Background
Sarcopenia is an age-related disease, which is characterized by a decline in muscle mass and function. It is one of the most important health issues in the elderly and often leads to a ...high rate and variety of adverse outcomes.
Objectives
To evaluate the screening accuracy of SARC-F for sarcopenia in the elderly.
Design
We conducted a meta-analysis using articles available in 6 databases including PubMed (Medline), Web of Science, Embase, Cochrane Controlled Register of Trials (CENTRAL), China Knowledge Resource Integrated Database (CNKI), and Wanfang databases from inception to May 2020. Participants: Adults aged 60 years and older.
Measurements
Sarcopenia was defined by EWGSOP2, EWGSOP, AWGS, FNIH and IWGS. Two authors independently extracted data based on predefined criteria. Where data were available we calculated pooled summary estimates of sensitivity, specificity, positive likelihood ratio (PLR), negative likelihood ratio (NLR), diagnostic odds ratio (DOR) and their 95% confidence interval (CI) based on different criteria using the hierarchical logistic regression modeling including bivariate modeling and hierarchical summary receiver operating characteristic (HSROC) modeling.
Results
We included 20 studies, with the prevalence of sarcopenia ranging from 6.42% to 21.56%. The number of the literatures using EWGSOP, EWGSOP2, AWGS, IWGS and FNIH as diagnostic criteria was 13, 4, 13, 8, 7, respectively. Bivariate analysis yielded a pooled sensitivity of 32% (95%CI: 19%–47%), 77% (95%CI: 49%–92%), 27% (95%CI: 16%–42%), 39% (95%CI: 27%–52%), 35% (95%CI: 23%–49%) and a pooled specificity of 86% (95%CI:77%–92%), 63% (95%CI: 43%–79%), 91% (95%CI: 85%–95%), 86% (95%CI: 76%–92%), 89% (95%CI: 81%–93%), respectively. The area under the HSROC curve were 0.68 (95%CI: 0.64–0.72), 0.75 (95%CI: 0.71–0.78), 0.73 (95%CI: 0.69–0.77), 0.67 (95%CI: 0.62–0.71), 0.70 (95%CI: 0.65–0.73), respectively.
Conclusions
The screening accuracy of SARC-F was various based on different diagnostic criteria. There were some limitations for SARC-F, however, considering the higher practicability and specificity for screening sarcopenia in practice, SARC-F was still an effective screening tool for sarcopenia in the elderly. And the screening accuracy of SARC-F needs further exploration when EWGSOP2 is applied as diagnostic criteria and geriatric inpatients are the target participants.
Composite structures made of 2 mm-thick titanium and 10 mm-thick carbon steel are widely used in infrastructures such as long-distance gas transportation. However, cracking, which is caused by ...intermetallic compounds (ICs), is a dominate failure mode in welds of this structure. Thus, a common way to improve the in-service life of is reduce the number of ICs. In this paper, we employ a novel hybrid welding method to fabricate composite structures of TA
titanium and Q235 carbon steel. Specifically, Ti and carbon steel is welded by laser and double Cold Metal Transfer (CMT) welding, respectively. The microstructure near the interface of Ti and steel is then examined using SEM, EBSD, EDS, with emphasis on the ICs in terms of chemical elements and morphologies. Results show that FeTi and Fe
Ti are the main ICs near the interface, and responsible for the failure of the welds. The effect of welding heat input on the formation of ICs is investigated as well. Results show that ICs are smaller when the heat input is low. Under low heat input circumstance, the tensile strength of the weld can reach up to 420 MPa.
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