Band inversions are key to stabilising a variety of novel electronic states in solids, from topological surface states to the formation of symmetry-protected three-dimensional Dirac and Weyl points ...and nodal-line semimetals. Here, we create a band inversion not of bulk states, but rather between manifolds of surface states. We realise this by aliovalent substitution of Nb for Zr and Sb for S in the ZrSiS family of nonsymmorphic semimetals. Using angle-resolved photoemission and density-functional theory, we show how two pairs of surface states, known from ZrSiS, are driven to intersect each other near the Fermi level in NbGeSb, and to develop pronounced spin splittings. We demonstrate how mirror symmetry leads to protected crossing points in the resulting spin-orbital entangled surface band structure, thereby stabilising surface state analogues of three-dimensional Weyl points. More generally, our observations suggest new opportunities for engineering topologically and symmetry-protected states via band inversions of surface states.
We present a revised and complete optical afterglow light curve of the binary neutron star merger GW170817, enabled by deep Hubble Space Telescope (HST) F606W observations at 584 days post-merger, ...which provide a robust optical template. The light curve spans 110-362 days, and is fully consistent with emission from a relativistic structured jet viewed off-axis, as previously indicated by radio and X-ray data. Combined with contemporaneous radio and X-ray observations, we find no spectral evolution, with a weighted average spectral index of 〈 β 〉 = − 0.583 0.013 , demonstrating that no synchrotron break frequencies evolve between the radio and X-ray bands over these timescales. We find that an extrapolation of the post-peak temporal slope of GW170817 to the luminosities of cosmological short gamma-ray bursts matches their observed jet break times, suggesting that their explosion properties are similar, and that the primary difference in GW170817 is viewing angle. Additionally, we place a deep limit on the luminosity and mass of an underlying globular cluster (GC) of L 6.7 × 103 L , or M 1.3 × 104 M , at least 4 standard deviations below the peak of the GC mass function of the host galaxy, NGC 4993. This limit provides a direct and strong constraint that GW170817 did not form and merge in a GC. As highlighted here, HST (and soon the James Webb Space Telescope) enables critical observations of the optical emission from neutron star merger jets and outflows.
Global dust storms (GDS) are an important dynamical phenomenon of the Martian lower atmosphere but are known to have important impacts on the Martian middle/upper atmosphere and ionosphere. Despite ...extensive studies over the past several decades, how the composition of the Martian ionosphere is modified during the GDS has only been studied from a theoretical point of view. Here we present for the first time the observations of the compositional variation of the Martian ionosphere during the GDS in 2018, using the ion density measurements made by the Neutral Gas and Ion Mass Spectrometer onboard the Mars Atmosphere and Volatile Evolution. At a representative altitude of 170 km, the variations of ionospheric species during the GDS show either enhancement (CO2+, Ar+, HO2+, H2O+, H2+, ArH+) or depletion (O2+, O+, N2+/CO+, OH+). Despite the apparent diversity, the observations are mostly understandable within the established framework of ionospheric chemistry on Mars, which further demonstrates that the variation of ion species during the GDS is a good diagnostic of the variation of relevant neutral species in the thermosphere. In particular, the observed ionospheric variation strongly supports a scenario that H2O is substantially enhanced in the Martian thermosphere during the GDS. However, the variations of O2+ and H2+ are inconsistent with predictions from ionospheric chemistry and require further investigation.
Plain Language Summary
Global dust storms (GDS) are an important dynamical phenomenon of the Martian climate that has been extensively studied over the past several decades. Though occurring in the lower atmosphere, they are known to have important impacts on the upper atmosphere and ionosphere, such as increasing the thermospheric water content, enhancing hydrogen escape, and lifting the ionospheric layer. Despite the existing efforts, how the composition of the Martian ionosphere is modified by has not been well studied. Owing to the accumulation of the ion density measurements made onboard the Mars Atmosphere and Volatile Evolution and the dust opacity measurements made onboard the Mars Reconnaissance Orbiter, we present for the first time a preliminary investigation of the species‐dependent variations of the dayside Martian ionosphere during the GDS in 2018. The responses of various ionospheric species to this event show diverse features, some demonstrating clear enhancement, whereas the others demonstrating clear depletion. Despite this, the observations are mostly consistent with the established ionospheric chemistry on Mars, implying that the variation of ionospheric species during a GDS is closely linked to the variation of neutral species in the thermosphere during the same event.
Key Points
Variations of the Martian ionosphere during global dust storms are species dependent, displaying either density enhancement or depletion
The variations of most ion species except for O2+ and H2+ are interpreted using the ionospheric chemistry on Mars
Substantial enhancement in thermospheric H2O on Mars during global dust storms are implied by ion measurements
Abstract
We investigate the effects of ram pressure on the molecular interstellar medium (ISM) in the disk of the Coma cluster galaxy NGC 4921 via high-resolution CO observations. We present 6″ ...resolution CARMA CO(1−0) observations of the full disk, and 0.″4 resolution Atacama Large Millimeter/submillimeter Array CO(2−1) observations of the leading quadrant, where ram pressure is strongest. We find evidence for compression of the dense ISM on the leading side, spatially correlated with intense star formation activity in this zone. We also detect molecular gas along kiloparsec-scale filaments of dust extending into the otherwise gas stripped zone of the galaxy, seen in Hubble Space Telescope images. We find the filaments are connected kinematically as well as spatially to the main gas ridge located downstream, consistent with cloud decoupling inhibited by magnetic binding, and inconsistent with a simulated filament formed via simple ablation. Furthermore, we find several clouds of molecular gas ∼1–3 kpc beyond the main ring of CO that have velocities that are blueshifted by up to 50 km s
−1
with respect to the rotation curve of the galaxy. These are some of the only clouds we detect that do not have any visible dust extinction associated with them, suggesting that they are located behind the galaxy disk midplane and are falling back toward the galaxy. Simulations have long predicted that some gas removed from the galaxy disk will fall back during ram pressure stripping. This may be the first clear observational evidence of gas re-accretion in a ram pressure stripped galaxy.
Well-crystallized, homogeneous nanocomposites of lithium iron(II) phosphate and carbon was synthesized by solid state reaction, and the obtained particles are spherical. Measurement of both CV and ...EIS shows that the lithium ion diffusion coefficient in the nanocomposites is affected by the incorporated carbon, and markedly increases with the carbon content. Meanwhile, the kinetics of lithium intercalation and de-intercalation is greatly ameliorated. These data provide strong evidence of the potential use of this kind of nanocomposite cathode in lithium ion battery.
Background
The rampant spread of the novel coronavirus disease (COVID‐19) has assumed pandemic proportions across the world. Attempts to contain its spread have entailed varying early screening and ...triage strategies implemented in different countries and regions.
Aim
To share the experience of scientific and standardized management of fever clinics in China, which provide the first effective checkpoint for the prevention and control of COVID‐19.
Introduction
A fever clinic was established at our hospital in Tianjin, China, for initially identifying suspected cases of COVID‐19 and controlling the spread of the disease.
Methods
The management system covered the following aspects: spatial layout; partitioning of functional zones; a work management system and associated processes; management of personnel, materials and equipment; and patient education.
Results
Within two months of introducing these measures, there was a comprehensive reduction in the number of new COVID‐19 cases in Tianjin, and zero infections occurred among medical staff at the fever clinic.
Discussion
The fever clinic plays an important role in the early detection, isolation and referral of patients presenting with fevers of unknown origin. Broad screening criteria, an adequate warning mechanism, manpower reserves and staff training at the clinic are essential for the early management of epidemics.
Conclusion
The spread of COVID‐19 has been effectively curbed through the establishment of the fever clinic, which merits widespread promotion and application.
Implications for nursing and health policies
Health managers should be made aware of the important role of fever clinics in the early detection, isolation and referral of patients, and in the treatment of infectious diseases to prevent and control their spread. In the early stage of an epidemic, fever clinics should be established in key areas with concentrated clusters of cases. Simultaneously, the health and safety of health professionals require attention.
Abstract
In this paper, the distribution of relaxation times (DRTs) functions are calculated numerically in Matlab for synthetic impedance data from single parallel
$$RC$$
RC
circuit and two parallel
...$$RC$$
RC
circuits connected in series, experimental impedance data from supercapacitors and α-LiFeO
2
anode based Li ion batteries. The quality of the impedance data is checked with the Kramers–Krönig (KK) relations. The DRTs are calculated within the KK compatible regime for all the systems using Tikhonov regularization (TR) method. Here we use a fast and simple L-curve method to estimate the TR parameter (λ) for regularization of the Fredholm integral equations of first kind in impedance. Estimation of the regularization parameters are performed effectively from the offset of the global corner of the L-curve rather than simply using the global corner. The physical significances of DRT peaks are also discussed by calculating the effective resistances and capacitances coupled with peak fitting program. For instance, two peaks in the DRTs justify the electrical double layer capacitance and ion diffusion phenomena for supercapacitors in low to intermediate frequencies respectively. Moreover, the surface film effect, Li/electrolyte and electrode/electrolyte charge transfer related processes are identified for α-LiFeO
2
anode based Li-ion batteries. This estimation of the offset of the global corner extends the L-curve approach coupled with the Tikhonov regularization in the field of electrochemistry and can also be applied in similar process detection methods.
Although fluorescence microscopy provides a crucial window into the physiology of living specimens, many biological processes are too fragile, are too small, or occur too rapidly to see clearly with ...existing tools. We crafted ultrathin light sheets from two-dimensional optical lattices that allowed us to image three-dimensional (3D) dynamics for hundreds of volumes, often at subsecond intervals, at the diffraction limit and beyond. We applied this to systems spanning four orders of magnitude in space and time, including the diffusion of single transcription factor molecules in stem cell spheroids, the dynamic instability of mitotic microtubules, the immunological synapse, neutrophil motility in a 3D matrix, and embryogenesis in Caenorhabditis elegans and Drosophila melanogaster. The results provide a visceral reminder of the beauty and the complexity of living systems.
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