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Fast radio bursts (FRBs) are millisecond-duration radio transients 1 , 2 of unknown origin. Two possible mechanisms that could generate extremely coherent emission from FRBs invoke neutron star magnetospheres 3 – 5 or relativistic shocks far from the central energy source 6 – 8 . Detailed polarization observations may help us to understand the emission mechanism. However, the available FRB polarization data have been perplexing, because they show a host of polarimetric properties, including either a constant polarization angle during each burst for some repeaters 9 , 10 or variable polarization angles in some other apparently one-off events 11 , 12 . Here we report observations of 15 bursts from FRB 180301 and find various polarization angle swings in seven of them. The diversity of the polarization angle features of these bursts is consistent with a magnetospheric origin of the radio emission, and disfavours the radiation models invoking relativistic shocks. Polarization observations of the fast radio burst FRB 180301 with the FAST radio telescope show diverse polarization angle swings, consistent with a magnetospheric origin of the emission.

Fast radio bursts (FRBs) are highly dispersed, millisecond-duration radio bursts 1 – 3 . Recent observations of a Galactic FRB 4 – 8 suggest that at least some FRBs originate from magnetars, but the origin of cosmological FRBs is still not settled. Here we report the detection of 1,863 bursts in 82 h over 54 days from the repeating source FRB 20201124A (ref.  9 ). These observations show irregular short-time variation of the Faraday rotation measure (RM), which scrutinizes the density-weighted line-of-sight magnetic field strength, of individual bursts during the first 36 days, followed by a constant RM. We detected circular polarization in more than half of the burst sample, including one burst reaching a high fractional circular polarization of 75%. Oscillations in fractional linear and circular polarizations, as well as polarization angle as a function of wavelength, were detected. All of these features provide evidence for a complicated, dynamically evolving, magnetized immediate environment within about an astronomical unit ( au ; Earth–Sun distance) of the source. Our optical observations of its Milky-Way-sized, metal-rich host galaxy 10 – 12 show a barred spiral, with the FRB source residing in a low-stellar-density interarm region at an intermediate galactocentric distance. This environment is inconsistent with a young magnetar engine formed during an extreme explosion of a massive star that resulted in a long gamma-ray burst or superluminous supernova. Analysis of a set of 1,863 bursts from the repeating source FRB 20201124A provides evidence of a complicated magnetized site within about an astronomical unit from the source in a barred galaxy.

Introduction Myasthenia gravis, which initially presents with prominent distal muscle weakness, is rare and is referred to as distal myasthenia gravis. Despite its clinical significance, the diagnosis of distal myasthenia gravis is often delayed or missed owing to mild and atypical symptoms. Case report We report the case of a 52-year-old ethnic Han woman who presented with task-related isolated transient right-hand weakness that began 15 years ago and lasted for 9 years without aggravation or improvement. In subsequent years, she developed right-hand stiffness with limited dexterity. More recently, this developed into bilateral hand weakness and simultaneous generalized weakness with ambulation, prompting suspicion of myasthenia gravis. Under Hertz repetitive nerve stimulation, the right facial nerve, right accessory nerve, right ulnar nerve, right radial nerve, and right median nerve showed decrements between 19.5% and 35.4%. Tests for anti-acetylcholine receptor antibodies were positive. The patient was diagnosed with distal myasthenia gravis, which evolved into generalized myasthenia gravis. Conclusion Distal myasthenia gravis can present with isolated and transient hand weakness as a lone symptom, and can persist for years before typical myasthenia gravis symptoms appear. The inclusion of myasthenia gravis in the differential diagnosis is necessary in patients with isolated distal weakness.

The extension of the cosmic-ray spectrum beyond 1 petaelectronvolt (PeV; 10 15 electronvolts) indicates the existence of the so-called PeVatrons—cosmic-ray factories that accelerate particles to PeV energies. We need to locate and identify such objects to find the origin of Galactic cosmic rays 1 . The principal signature of both electron and proton PeVatrons is ultrahigh-energy (exceeding 100 TeV) γ radiation. Evidence of the presence of a proton PeVatron has been found in the Galactic Centre, according to the detection of a hard-spectrum radiation extending to 0.04 PeV (ref. 2 ). Although γ-rays with energies slightly higher than 0.1 PeV have been reported from a few objects in the Galactic plane 3 – 6 , unbiased identification and in-depth exploration of PeVatrons requires detection of γ-rays with energies well above 0.1 PeV. Here we report the detection of more than 530 photons at energies above 100 teraelectronvolts and up to 1.4 PeV from 12 ultrahigh-energy γ-ray sources with a statistical significance greater than seven standard deviations. Despite having several potential counterparts in their proximity, including pulsar wind nebulae, supernova remnants and star-forming regions, the PeVatrons responsible for the ultrahigh-energy γ-rays have not yet been firmly localized and identified (except for the Crab Nebula), leaving open the origin of these extreme accelerators. Observations of γ-rays with energies up to 1.4 PeV find that 12 sources in the Galaxy are PeVatrons, one of which is the Crab Nebula.

Fast radio bursts (FRBs) are millisecond-duration radio transients of unknown physical origin observed at extragalactic distances 1 – 3 . It has long been speculated that magnetars are the engine powering repeating bursts from FRB sources 4 – 13 , but no convincing evidence has been collected so far 14 . Recently, the Galactic magnetar SRG 1935+2154 entered an active phase by emitting intense soft γ-ray bursts 15 . One FRB-like event with two peaks (FRB 200428) and a luminosity slightly lower than the faintest extragalactic FRBs was detected from the source, in association with a soft γ-ray/hard-X-ray flare 18 – 21 . Here we report an eight-hour targeted radio observational campaign comprising four sessions and assisted by multi-wavelength (optical and hard-X-ray) data. During the third session, 29 soft-γ-ray repeater (SGR) bursts were detected in γ-ray energies. Throughout the observing period, we detected no single dispersed pulsed emission coincident with the arrivals of SGR bursts, but unfortunately we were not observing when the FRB was detected. The non-detection places a fluence upper limit that is eight orders of magnitude lower than the fluence of FRB 200428. Our results suggest that FRB–SGR burst associations are rare. FRBs may be highly relativistic and geometrically beamed, or FRB-like events associated with SGR bursts may have narrow spectra and characteristic frequencies outside the observed band. It is also possible that the physical conditions required to achieve coherent radiation in SGR bursts are difficult to satisfy, and that only under extreme conditions could an FRB be associated with an SGR burst. An 8-hour radio observational campaign of the Galactic magnetar SGR 1935+2154, assisted by multi-wavelength data, indicates that associations between fast radio bursts and soft γ-ray bursts are rare.

Spider pulsars are neutron stars that have a companion star in a close orbit. The companion star sheds material to the neutron star, spinning it up to millisecond rotation periods, while the orbit shortens to hours. The companion is eventually ablated and destroyed by the pulsar wind and radiation 1 , 2 . Spider pulsars are key for studying the evolutionary link between accreting X-ray pulsars and isolated millisecond pulsars, pulsar irradiation effects and the birth of massive neutron stars 3 – 6 . Black widow pulsars in extremely compact orbits (as short as 62 minutes 7 ) have companions with masses much smaller than 0.1  M ⊙ . They may have evolved from redback pulsars with companion masses of about 0.1–0.4  M ⊙ and orbital periods of less than 1 day 8 . If this is true, then there should be a population of millisecond pulsars with moderate-mass companions and very short orbital periods 9 , but, hitherto, no such system was known. Here we report radio observations of the binary millisecond pulsar PSR J1953+1844 (M71E) that show it to have an orbital period of 53.3 minutes and a companion with a mass of around 0.07  M ⊙ . It is a faint X-ray source and located 2.5 arcminutes from the centre of the globular cluster M71. PSR J1953+1844 (M71E) has an orbital period of 53.3 minutes and a companion with a mass of 0.07  M ⊙ , making it a bridging object between redbacks and black widows in the evolutionary track.

Leaf area index (LAI) is one of the key structural variables in terrestrial vegetation ecosystems. Remote sensing offers an opportunity to accurately derive LAI at regional scales. The anisotropy of canopy reflectance, variations in background characteristics, and variability in atmospheric conditions constitute three factors that can strongly constrain the accuracy of retrieved LAI. Based on a hybrid canopy reflectance model, a new hyperspectral directional second derivative method (DSD) is proposed in this paper. This method can estimate LAI accurately through analyzing the canopy anisotropy. The effect of the background can also be effectively removed. With the aid of a widely-accepted atmospheric model, the influence of atmospheric conditions can be minimized as well. Thus the inversion precision and the dynamic range can be markedly improved, which has been proved by numerical simulations. As the derivative method is very sensitive to random noise, we put forward an innovative filtering approach, by which the data can be de-noised in spectral and spatial dimensions synchronously. It shows that the filtering method can remove random noise effectively; therefore, the method can be applied to hyperspectral images. The study region was situated in Zhangye, Gansu Province, China; hyperspectral and multi-angular images of the study region were acquired via the Compact High-Resolution Imaging Spectrometer/Project for On-Board Autonomy (CHRIS/PROBA), on 4 June 2008. After the pre-processing procedures, the DSD method was applied, and the retrieved LAI was validated by ground reference data at 11 sites. Results show that the new LAI inversion method is accurate and effective with the aid of the innovative filtering method.

The wettability of metal surfaces is of importance in different practical applications. In the present work, we investigated the role of alumina coatings in the variation of the surface wettability of aluminum alloys by nanosecond laser ablation. The superhydrophilic surface (water contact angle close to 0°) was successfully prepared, and the superhydrophilic surface was transformed into the superhydrophobic surface (water contact angle of about 151.4°) after non-fluorinated N-octyltriethoxysilane (OcTES) treatment. XPS results showed that the Al–OH (–OH) hydrophilic groups generated by coating decomposition occupied the main regions on the surface after laser ablation. After OcTES treatment, the OcTES molecules formed Si–O–Al bonds with the rough surface, which significantly increased the C–C(H) hydrophobic groups of the surface. The superhydrophobic surface showed good self-cleaning, anti-icing and anti-corrosion properties. The fabrication method is fast, non-toxic and environmentally friendly, which makes it potentially useful for engineering applications.

Pulsars radiate radio signals when they rotate. However, some old pulsars often stop radiating for some periods. The underlying mechanism remains unknown, as the magnetosphere during nulling phases is hard to probe due to the absence of emission measurements. Here we report the detection and accurate polarization measurements of sporadic, weak, narrow dwarf pulses detected in the ordinary nulling state of pulsar B2111+46 via the Five-Hundred-Meter Aperture Spherical radio Telescope. Further analysis shows that their polarization angles follow the average polarization angle curve of normal pulses, suggesting no change of the magnetic-field structure in the emission region in the two emission states. Whereas radio emission of normal individual pulses is radiated by a ‘thunderstorm’ of particles produced by copious discharges in regularly formed gaps, dwarf pulses are produced by one or a few ‘raindrops’ of particles generated by pair production in a fragile gap of this near-death pulsar.The intensity of radio emission from a pulsar is shown to relate to the quantity of particles discharging in the magnetosphere rather than to changes of the structure of the magnetic field in the magnetosphere itself.