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Higher-order topological insulators (HOTIs) are systems with topologically protected in-gap boundary states localized at their $(d-n)$-dimensional boundaries, with $d$ the system dimension and $n$ the order of the topology. This work proposes a rather universal dynamics-based characterization of one large class of $Z$-type HOTIs without specifically relying on any symmetry considerations. The key element of our innovative approach is to connect quantum quench dynamics with nested configurations of the so-called band inversion surfaces (BISs) of momentum-space Hamiltonians as a sum of operators from the Clifford algebra (a condition that can be relaxed), thereby making it possible to dynamically detect each and every order of topology on an equal footing. Given that experiments on synthetic topological matter can directly measure the winding of certain pseudospin texture to determine topological features of BISs, the topological invariants defined through nested BISs are all within reach of ongoing experiments. Further, the necessity of having nested BISs in defining higher-order topology offers a unique perspective to investigate and engineer higher-order topological phase transitions., Comment: 15 pages and 7 figures in total. Comments are welcome

Ultrasmall nitrogen-doped carbon-coated CoSe2/ZnSe nanospheres (CoSe2/ZnSe@C nanospheres) are fabricated by direct selenization of a delicately designed Co1.6Zn0.4-(benzimidazole)4 metal–organic framework (MOF) nanosheet precursor and used as the anode materials in sodium-ion batteries (SIBs). The fabricated CoSe2/ZnSe@C nanospheres deliver a remarkable rate performance (395 mAh g−1 at 0.1 A g−1 and 341 mAh g−1 at 5.0 A g−1) and excellent long-term durability (346 mAh g−1 after 2500 cycle at 2.0 A g−1). The superior Na storage performance of the fabricated CoSe2/ZnSe@C nanospheres could be mainly attributed to their ultrasmall particle sizes and the phase boundaries between CoSe2 and ZnSe, which improve the kinetics of the electrode, relieve the volume change during the charge/discharge process, and provide extra Na+ storage sites. This work opens up possibilities to fabricate metal selenide–based hybrid materials with desired nanostructures and compositions from rationally designed multimetal MOF precursors for high-performance anode materials in SIBs.

Application of nitrogen-doped carbon for electroreduction of CO2 to CO receives increasing attentions, and improving the CO selectivity of carbon-based materials is prominent. Here we introduce a halogen-assisted calcination strategy for constructing two-dimensional (2D) nitrogen-doped carbon from ZIF-8 precursor. Benefitting from the abundant graphitic-N (G-N) and the enlargement of electrochemical surface area (ECSA), 2D nitrogen-doped carbon presents excellent catalytic activity with the high faradaic efficiency (FE) of CO reaching 99.5% and current density of −2.6 mA cm−2 at a low potential of −0.5 V (vs. RHE) in H-type cell, with the long-term stability up to more than 20 h. A positive correlation between FECO and the ratio of G-N (the ratio of graphitic-N content to total N content.) is revealed. The halogen-assisted calcination can effectively increase the G-N ratio and enlarge ECSA, thereby increasing FECO, which is a promising strategy for improving CO selectivity of carbonaceous materials.

More than 50 years after the discovery of pulsars1 and confirmation of their association with supernova explosions2–4, the origin of the initial spin and velocity of pulsars remains largely a mystery. The typical space velocities of several hundred km s−1 have been attributed to ‘kicks’ resulting from asymmetries either in the supernova ejecta or in the neutrino emission5–7. Observations have shown a strong tendency for alignment between the pulsar space velocity and the spin axis in young pulsars, but until now these comparisons have been restricted to two dimensions. Here, we report evidence for three-dimensional alignment between the spin and velocity vectors, largely based on observations made with the Five-hundred-meter Aperture Spherical Radio Telescope (FAST) of the pulsar PSR J0538+2817 and its associated supernova remnant S147. Analysis of these and related observations has enabled us to determine the location of the pulsar within the supernova remnant and hence its radial velocity. Current simulations of supernova explosions have difficulty producing such three-dimensional alignment7–9. Our results, which depend on the unprecedented sensitivity of the observations, add another dimension to the intriguing correlation between pulsar spin-axis and birth-kick directions, thereby deepening the mysteries surrounding the birth of neutron stars. Fast-moving pulsars and neutron stars in general may have received a kinetic ‘kick’ from an asymmetric element in the supernova explosion that formed them. Here, the spin axis of a pulsar is determined to lie along the three-dimensional direction of the pulsar’s motion, providing a challenging constraint on supernova explosion modelling.

Sliding wear-induced nanolayering and its positive impact on wear resistance have been observed in conventional binary alloys with a matrix of high stacking fault energy (SFE), but this concept has never been reported in high-entropy alloys (HEAs) with low SFE. Here, we design and fabricate a (CoCrFeNi)90Ag10 HEA, consisting of a face-center-cubic (fcc) CoCrFeNi HEA matrix with low SFE and uniformly dispersed Ag precipitates. In comparison with CoCrFeNi, a significant reduction in friction and wear was found in (CoCrFeNi)90Ag10 HEA through the spontaneous formation of nanolayered subsurface microstructure during wear. The finding suggests a novel approach for designing HEAs that can achieve low friction and wear.

The current water shortage in China is critical. Moreover, the water shortage has become the main bottleneck hindering sustainable economic growth. Against the background of China's dual control target of total water use and intensity, we choose the Yangtze River Delta (YRD) region as a research object, which encompasses Shanghai, Jiangsu, Zhejiang, and Anhui. Based on the perspective of water-energy-food nexus, we employ the generalized Divisia index method to decompose the change of water use into eight factors, regional economic scale effect, regional energy use scale effect, regional food production effect, regional water technology effect, regional energy technology effect, regional water-energy nexus effect, regional food-energy nexus effect, and regional water technology for food production effect, and analyze the contribution of each driver to identify the key drivers of total water use control. The results showed that the top four influencing factors are GDP, water intensity, energy consumption, and water-energy nexus in the YRD region. Regional economic scale is the first driving factor for increasing water use in the YRD region except for Zhejiang. Water intensity is the primary driving force of water-saving in Zhejiang. Energy consumption is the third driver of increasing water use in Jiangsu and Anhui. The effect of water-energy nexus is the third driving factor that affects the change of water use in Shanghai and Zhejiang. The authorities in the YRD region should vigorously develop water and energy utilization technologies to increase the water intensity and decrease energy consumption. The energy sector should decrease the water use to decrease the water-energy nexus which is also the main driving factor affecting the change of water use.

The development of organic nanoparticles that fluoresce in the near-infrared, especially in the second near-infrared (NIR-II) window, improves in vivo fluorescence imaging due to deeper penetration and higher spatiotemporal resolution. We report two kinds of NIR-II fluorescent molecules with twisted intramolecular charge-transfer (TICT) and aggregation-induced emission (AIE) characteristics. The virus-like particles (VLPs) of simian virus 40 (SV40) were used as templates to encapsulate the molecules in a well-defined structure (referred to as CH1-SV40 and CH2-SV40). The CH1-SV40 dots exhibited a highly uniform size of 21.5 nm, strong fluorescence, high photostability, and good biocompatibility in vitro and in vivo. Their fluorescence spectrum exhibited a peak at 955 nm, with a tail extending to 1200 nm. Moreover, the CH1-SV40 dots, with a quantum yield of 13.03%, enabled blood vessel imaging and image-guided surgery with a high signal-to-background ratio. Overall, the hybrid nanoparticles represent a new kind of NIR-II AIE nanoprobes for biomedical imaging.

The creep behavior of Fe–17Cr–1.2Cu–0.5Nb–0.01C ferritic heat-resistant stainless steel was investigated at temperatures ranging from 973 to 1123 K and stresses from 15 to 90 MPa. The evolution of precipitates after creep deformation was analyzed by scanning electron microscopy, energy dispersion spectrum, and transmission electron microscopy. The minimum creep rate decreased with the decrease in the applied load and temperature, thereby extending the rupture life. Cu-rich phase and Nb-rich Laves particles were generated in dominant quantities during the creep process, and the co-growth relationship between them could be detected. Creep rupture was featured by ductile fracture with considerable necking. As increasing the temperature and decreasing the stress, the softening of the metal matrix was accelerated, showing more obvious plastic flow. The true stress exponent and activation energy were 4.9 and 375.5 kJ/mol, respectively, indicating that the creep deformation was dominated by the diffusion-controlled dislocation creep mechanism involving precipitate-dislocation interactions. Based on the creep rupture data obtained, the Monkman–Grant relation and Larson-Miller parameter were established, which described the creep rupture life for the studied steel well.

Elevated levels of reactive oxygen species (ROS) are implicated in the onset and progression of many diseases, e.g., virus infection, ischemic stroke and neurodegenerative diseases. ROS-scavenging nanomaterials have attracted particular interest. Here, we report the development of a natural protein nanocage named Dps for in vitro and in vivo antioxidant treatment by inhibiting the Fenton reaction, a critical step in ROS generation and interconversion. Systematic surface engineering enabled cell penetration, good colloidal stability, and facile purification of Dps. With its intrinsic ferroxidase activity consuming both H2O2 and Fe2+, Dps not only protects human cells from oxidative stress but also effectively alleviates ROS-induced inflammation in a mouse dermatitis model. The protection is triggered by elevated H2O2 and thereby, in principle, avoids ROS imbalances. Thus, Dps has potential as a new bionano platform for different purposes, such as antiaging, anti-inflammation and cosmetics.

In this paper, a novel Dy2O3-Al2O3-SiO2 (DAS) glass ceramic was designed and prepared for joining zirconia toughened alumina (ZTA) ceramic. The crystallization, thermal expansion behavior and wetting behavior of the DAS glass filler were studied. The effect of cooling rate and joining temperature on the microstructure and flexural strength of joints was investigated. The results show that slow cooling rate (15 °C/min) leads to crystallization of brazing seam, which causes the formation of pores in the joints due to the large density difference between the glass and the crystalline phases. The dissolution of ZrO2 from ZTA substrate into the filler during joining process improves the mismatch of the coefficient of thermal expansion (CTE) between the brazing seam and substrate. The maximum flexural strength of 535 MPa is obtained when the joining temperature and cooling rate are 1475 °C and 50 °C/min, respectively.

Air quality in China is increasingly improving, but the situation facing the atmosphere environment is still dire. Regional atmospheric environmental problems characterized by PM2.5 pollutants are becoming increasingly prominent, especially in the Jing-Jin-Ji (3J) region. This study employs the generalized Divisia index approach to decompose the factors that influence the changes of PM2.5 emission in the 3J region. It is divided into 8 factors: scale effect of regional economy, scale effect of regional energy consumption, scale effect of investment in treatment of environment pollution (ITEP), technology effect of energy efficient utilization, technology effect of clean energy utilization technology, the intensity effect of regional green economic development, the intensity effect of investment in treatment of regional PM2.5 emission, and the intensity effect of regional environmental regulation. To identify the vital driving force of the change of PM2.5 emission, the contribution of each driving factor of PM2.5 emission variation is analyzed. The results show that the factors affecting the change of PM2.5 emission are almost the same, but the contribution of each factor is apparently different in the 3J region. The level of regional economic development and the scale of energy consumption promoted the increase of PM2.5 emission in the region. The growth of PM2.5 emission can be effectively controlled by green economic development intensity, energy clean utilization technology, environmental regulation intensity, and the intensity of investment in treatment of PM2.5 emission. Energy efficiency has a slight effect on the changes of PM2.5 emission. ITEP has a negative effect on the changes of PM2.5 emission. In the future, the 3J region needs to optimize the structure of ITEP further and implement the refinement and precision of pollution treatment. Moreover, it also needs to promote the development of energy clean and efficient use of technological innovation to drive PM2.5 emission reduction.

A palladium-catalyzed cross-coupling reaction with aryl halide functionalities has recently emerged as a valuable tool for protein modification. Herein, a new fluorogenic modification methodology for proteins, with genetically encoded fluorosulfate-l-tyrosine, which exhibits high efficiency and biocompatibility in bacterial cells as well as in aqueous medium, is described. Furthermore, the cross-coupling of 4-cyanophenylboronic acid on green fluorescent protein was shown to possess a unique fluorogenic property, which could open up the possibility of a responsive "off/on" switch with great potential to enable spectroscopic imaging of proteins with minimal background noise. Taken together, a convenient and efficient catalytic system has been developed that may provide broad utilities in protein visualization and live-cell imaging.

Indazolone cores are among the most common structural components in medicinal chemistry and can be found in many biologically active molecules. In this report, a mild and efficient approach to 2-su...

The face-centered-cubic (fcc) CoCrFeMnNi high-entropy alloy suffers from low strength and wear resistance at ambient temperature. Herein, we developed a strategy to overcome the strength/ductility trade-off and simultaneously increase the wear resistance via the in situ formation of uniformly dispersed Mn3O4 nanoparticles in an ultrafine-grained fcc FeMnNi matrix. The obtained equiatomic FeMnNi alloy exhibited a high yield strength of up to 912 MPa and an elongation of 19 pct. Grain boundary and oxide-dispersion-strengthened were found to be the main strengthening mechanisms. Ball-on-disk wear tests showed that the FeMnNi alloy had low wear rates in the order of 10−4-10−5 mm3/(N m) upon sliding against an alumina ball, and the wear mechanism changed from abrasive wear to oxidation and fatigue wear at high loads and sliding velocities. The presence of Mn3O4 nanoparticles hindered the severe plastic flow of the fcc matrix during sliding. The excellent combination of strength, ductility, and tribological performance of the present alloy renders it as a promising candidate for structural applications.

Titanium alloys have been widely used for medical devices and structural applications. However, conventional titanium alloys often suffer from low resistance to wear, particularly at elevated temperatures. Herein, an equiatomic TiMoNb compositionally complex alloy (CCA) is shown to exhibit wear resistance comparable to alumina at room temperature (RT). Even at 600 °C, the alloy still shows an extremely low wear rate of the order of 10−6 mm3/(N·m). The remarkable wear resistance is achieved via tuning the interfacial structure and chemistry in TiMoNb CCA, including nanostructuring, titanium segregation at the grain boundaries, and the formation of a high density of nanoscale coherent Ti-rich precipitates with cube-on-cube orientation relationship with the ultrafine-grained matrix. The present results provide significant insights into the design of novel alloys for service in harsh environments.

Two-dimensional (2D) metal–organic frameworks (MOFs) and their derivatives with excellent dimension-related properties, e.g. high surface areas, abundantly accessible metal nodes, and tailorable structures, have attracted intensive attention as energy storage materials and electrocatalysts. A major challenge on the road toward the commercialization of 2D MOFs and their derivatives is to achieve the facile and controllable synthesis of 2D MOFs with high quality and at low cost. Significant developments have been made in the synthesis and applications of 2D MOFs and their derivatives in recent years. In this review, we first discuss the state-of-the-art synthetic strategies (including both top-down and bottom-up approaches) for 2D MOFs. Subsequently, we review the most recent application progress of 2D MOFs and their derivatives in the fields of electrochemical energy storage (e.g., batteries and supercapacitors) and electrocatalysis (of classical reactions such as the HER, OER, ORR, and CO2RR). Finally, the challenges and promising strategies for the synthesis and applications of 2D MOFs and their derivatives are addressed for future development.

China's economy in the past 10 years has developed rapidly and achieved great success, but at the same time, environmental problems have been deteriorating, seriously hindering the country's regional sustainable development. This paper proposes a common-weights DEA model based on "the priority of choosing common weights" to assess the environmental performance of 30 provinces from 2006 to 2015 and analyzes regional development in combination with China's economic division. This paper also introduces the biennial Malmquist Productivity Index (BMPI) to study environmental productivity levels during the 11th and 12th Five Year Plans (FYP) from a time series perspective. The results present a large gap in regional environmental efficiency, mainly manifested by the fact that the eastern and northeastern regions' environmental condition is obviously better than that of the central and western regions. BMPI analysis indicates that the overall environmental performances during the 11th and 12th FYPs did not improve significantly, with a clear imbalance in the western region, implying that its development potential is huge. On this basis, we offer some suggestions for improving the environmental performance of different regions.

The development of nonprecious metal-nitrogen-carbon (M-N-C) materials with efficient metal utilization and abundant active sites for the oxygen reduction reaction (ORR) is of great significance for fuel cells and metal-air batteries. Ultrasmall 2 D Cox Zn2-x (benzimidazole)4 [Cox Zn2-x (bim)4 ] bimetallic metal-organic framework (MOF) nanosheets (≈2 nm thick) are synthesized by a novel bottom-up strategy and then thermally converted into a core-shell structure of sub-5 nm Co nanodots (NDs) wrapped with 2 to 5 layers of Co,N-codoped graphene (Co@FLG). The size of the Co NDs in Co@FLG could be precisely controlled by the Co/Zn ratio in the Cox Zn2-x (bim)4 nanosheet. As an ORR electrocatalyst, the optimized Co@FLG exhibits an excellent half-wave potential of 0.841 V (vs. RHE), a high limiting current density of 6.42 mA cm-2 , and great stability in alkaline electrolyte. Co@FLG also has great ORR performance in neutral electrolyte, as well as in Mg-air batteries. The experimental studies and DFT calculations reveal that the high performance of Co@FLG is mainly attributed to its great O2 absorptivity, which is endowed by the abundant Co-Nx and pyridinic-N in the FLG shell and the strong electron-donating ability from the Co ND core to the FLG shell. This elevates the eg orbital energy of CoII and lowers the activation energy for breaking the O=O/O-O bonds. This work sheds light on the design and fabrication of 2 D MOFs and MOF-derived M-N-C materials for energy storage and conversion applications.

CaO–Al2O3–SiO2–TiO2 glass ceramic filler with high crystallinity was used for joining alumina ceramic. The influence of joining temperature and crystallization treatment on the microstructure and flexural strength of joints was studied. The results demonstrated that a joining temperature higher than the melting temperature of crystals was essential to obtain dense joints. Furthermore, the formation of CaAl2Si2O8 at the alumina/glass filler interface decreased the flexural strength of joints due to the mismatch of coefficient of thermal expansion (CTE) between CaAl2Si2O8 and substrate. The maximum flexural strength of 256 MPa at room temperature was achieved when the joining temperature was 1260 °C. After crystallization treatment, a large number of fine CaTiSiO5 was precipitated in the brazing seam. The flexural strength of joints after crystallization at room temperature was 221 MPa, and increased to 242 MPa at 800 °C. These results can be attributed to the change of CTE value of the brazing seam.

Global climate change and human activities have resulted in immense changes in the Earth’s ecosystem, and the interaction between the land surface and the atmosphere is one of the most important processes. Wind is a reference for studying atmospheric dynamics and climate change, analyzing the wind speed change characteristics in historical periods, and studying the influence of wind on the Earth-atmosphere interaction, additionally, studying the wind, contributes to analyzing and alleviating a series of problems, such as the energy crisis, environmental pollution, and ecological deterioration facing human beings. In this study, data from 697 meteorological stations in China from 2000 to 2019 were used to study the distribution and trend of wind speed over the past two decades. The relationships between wind speed and climate factors were explored using statistical methods, furthermore, combined with terrain, climate change, and human activities, we quantified the contribution of environmental factors to wind speed. The results show that a downward trend was recorded before 2011, but overall, there was an increasing trend that was not significant, moreover, the wind speed changes showed obvious seasonality and were more complicated on the monthly scale. The wind speed trend mainly increased in the western region, decreased in the eastern region, was higher in the northeastern, northwestern, and coastal areas, and was lower in the central area. Temperature, bright sunshine duration, evaporation, and precipitation had a strong influence, in which wind speed showed a significant negative correlation with temperature and precipitation and vice versa for sunshine and evapotranspiration. The influence of environmental factors is diverse, and these results could help to develop environmental management strategies across ecologically fragile areas and improve the design of wind power plants to make better use of wind energy.

Tumor targeting with nanoparticles is a promising strategy for cancer diagnosis and treatment, especially for drug delivery to solid tumors. Previous studies mainly focused on nanoparticle design to improve their targeting efficiency, but few have investigated the impact of tumor progression stages on the targeting efficiency. Here, we used PEGylated viral nanoparticles (VNPs) of bacteriophage P22 to explore the relationship between targeting efficiency and tumor progression stages using a colorectal cancer model. We found an 8.1-fold increase in the accumulation of P22 VNPs systematically injected 7 days after tumor inoculation compared with those injected 21 days after tumor inoculation. Most tumor-targeted P22 VNPs were concentrated in tumor-associated macrophages in the tumor blood vessels, the density of which decreased with the progression of tumors. These results reveal that the tumor targeting efficiency of P22 VNPs decreased with tumor progression. These findings provide valuable information for not only the understanding of controversial observations regarding targeted cancer therapy in experimental and clinical studies but also the design of nanoparticle-based tumor targeting probes or therapeutics.

The non-Hermitian skin effect (NHSE) in non-Hermitian lattice systems depicts the exponential localization of eigenstates at system's boundaries. It has led to a number of counter-intuitive phenomena and challenged our understanding of bulk-boundary correspondence in topological systems. This work aims to investigate how the NHSE localization and topological localization of in-gap edge states compete with each other, with several representative static and periodically driven 1D models, whose topological properties are protected by different symmetries. The emerging insight is that at critical system parameters, even topologically protected edge states can be perfectly delocalized. In particular, it is discovered that this intriguing delocalization occurs if the real spectrum of the system's edge states falls on the same system's complex spectral loop obtained under the periodic boundary condition. We have also performed sample numerical simulation to show that such delocalized topological edge states can be safely reconstructed from time-evolving states. Possible applications of delocalized topological edge states are also briefly discussed., Comment: 9 pages, 8 figures, comments are welcome

Direct electrochemical reduction of CO2 to multicarbon products is highly desirable, yet challenging. Here, we present a potentiostatic pulse-electrodeposition of high-aspect-ratio CuxAuy nanowire arrays (NWAs) as high-performance electrocatalysts for the CO2 reduction reaction (CO2RR). The surface electronic structure related to the Cu:Au ratio in the CuxAuy NWAs could be facilely modulated by controlling the electrodeposition potential and the as-fabricated CuxAuy NWAs could be directly used as the catalytic electrode for the CO2RR. The morphology of the high-aspect-ratio nanowire array significantly lowers the onset potential of the alcohol formation due to the diffusion-induced enhancement of the local pH and CO concentration near the nanowire surface. Besides, the properly adjusted surface electronic structure of the CuxAuy NWA enables the adsorption of CO and facilitates the subsequent CO reduction to ethanol via the C-C coupling pathway. Owing to the synergistic effect of morphology and electronic structure, the optimized CuxAuy NWA selectively reduces CO2 to ethanol at low potentials of −0.5–−0.7 V vs. RHE with a highest Faradaic efficiency of 48%. This work demonstrates the feasibility to optimize the activity and selectivity of the Cu-based electrocatalysts toward multicarbon alcohols for the CO2RR via simultaneous adjustment of the electronic structure and morphology of the catalysts.

Lead halide perovskite quantum dots (PQDs) have recently been proposed as scalable and color-tunable single emitters, but their slow spontaneous emission (1–10 ns) creates a mismatch with high-spee...

In the present work, wetting behaviour of Ag–Cu eutectic filler on high nitrogen austenitic stainless steel (HNS) and 316L austenitic stainless steel (316L) base metals was firstly studied using a sessile drop method in high vacuum. The Ag–Cu eutectic filler exhibits completely different dynamic wetting process on the surface of HNS and 316L. The equilibrium contact angle of Ag–Cu/HNS system is lower and its wetting time is shorter than that of Ag–Cu/316L system. Subsequently, brazing experiments were carried out for HNS and 316L base metals using the same filler at 840 °C for a holding period of 5–30 min under high vacuum. Microstructural analysis shows that the 316L/316L joints are composed of α-Cu and fine Ag–Cu eutectic. The HNS/HNS joints consist of β-Ag and coarse Ag–Cu eutectic. The optimal shear strength of HNS/HNS joints (290 MPa) is significantly higher than that of 316L/316L joints (175 MPa) because of the formation of diffusion layer. Therefore, HNS has tremendous potential to take the place of the traditional austenitic stainless steels for industry application.

Although dilute Cu-Cr alloys are frequently used for applications involving sliding contacts, their wear mechanism at elevated temperatures has rarely been explored. We fabricated a bulk Cu-6 wt pct Cr alloy using high-energy ball milling and spark plasma sintering, and systematically investigated its dry sliding wear behavior against 440C stainless steel at room temperature and 300 °C. The alloy had a heterogeneous microstructure consisting of coarse-grained Cu (average grain size: 1.5 µm) distributed into a nanocrystalline Cu-Cr matrix (average Cu grain size: 77 nm; Cr-rich precipitate size: 18 nm), which gave high strength and plasticity (ultimate compressive strength: 1020 MPa; strain-to-failure: 26.0 pct) at room temperature. At 300 °C, the strength was significantly reduced, the coefficient of friction and wear rate increased, and the dominant wear mode switched from adhesive wear to oxidative/abrasive wear. Uniformly distributed nanoscale Cr-rich and Cr oxide precipitates hindered severe plastic deformation near the sliding surface during wear at room temperature; at 300 °C, severe plastic deformation was observed, with elongated Cu grains and uniformly dispersed Cr-rich and Cr oxide nanoparticles. Formation of a discontinuous glaze layer consisting of equiaxed nanograins of Cu, Cu oxides, and Cr oxides resulted in severe abrasion-assisted wear, and reduced the wear resistance at 300 °C.

A kind of n–p (SnO2)1.3/(α ∼ Bi2O3)x/(β ∼ Bi2O3)1−x nanocomposite (SB-15) was synthesized with polyvinyl alcohol (PVA) as a template by solid state synthesis. XRD and HR-TEM confirmed the formation of n–p (SnO2)1.3/(α ∼ Bi2O3)x/(β ∼ Bi2O3)1−x. Particle size is found to be about 18 nm from HR-TEM images. FE-SEM clearly detected the boundary between SnO2 nanoparticles and Bi2O3 polyhedron particles. The special morphology and coexisting of α-Bi2O3 and β-Bi2O3 in SB-15 make it have a stronger visible light absorption range as far as 725 nm. PL and photocurrent test shows that the SB-15 has the best photocarriers separation capability. About 99% decolorization ratio of Rh.B was achieved in only 5 min. About 70% Cr6+ was degraded within 20 min and it is about 60% for tetracycline in the coexisting system (Te with Cr6+ solution), introducing it as a promising photocatalytic material. This work has addressed the method of phase-selective synthesis of n–p SnO2/α ∼ Bi2O3/β ∼ Bi2O3 by convenient solid state synthesis, which should be useful for the studies of other composites.

This study establishes a dynamic model of a new brake system with two-layer structure to explore the mechanism of vibration and noise reduction of a brake pad with new structure. The model is used to analyze the effects of parameters of the double-layer pad on the stability and stick-slip vibration characteristics of the brake system. The stability of the brake system is optimized by brake parameters with respect to the stability diagram of brake pressure under a relatively wide range. System vibration modes can be changed from period-doubling bifurcation to chaos based on the variation of brake pressure and the parameters of double-layer pad via numerical analysis. The chaotic vibration region is optimized in this study using the correlation coefficient, which consists of friction-layer pad mass mb2 and connection stiffness k2. Results show that the range of chaotic vibration region can be reduced when the friction-layer pad mass and connection stiffness are large.

Low-frequency/resonance magnetoelectric interactions and power conversion efficiency of magnetoelectric gyrators consisting of compositionally-graded nickel zinc ferrites and lead zirconate titanate with a coil wound around it were proposed and systematically characterized. Grading-induced differences of magnetic moment and remnant magnetization in ferrites with composition of Ni1−xZnxFe2O4 (0 ≤ x ≤ 0.3) can create the desired built-in field to decrease the required bias. The samples were characterized in terms of magnetostriction, low-frequency/resonance and power conversion efficiency with varieties of Zn concentrations, reversal sequence and volume ratio. A maximum PE of 62.9% was achieved in the composite of PZT-NiFe2O4-Ni0.9Zn0.1Fe2O4 at H = 10 Oe with volume ratio n = 0.5 under load RL = 700 Ω. With contribution of the desired built-in field, maximum PE of 60% under zero bias was also achieved in similar conditions. These favorable features open up the possibilities of ME gyrators with grading for promising applications in power electronics, converters and wireless energy harvesters without a sacrifice in device volume and modest rise in magnetomechanical efficiency.

Herein, we report an ethanothermal synthesis of multicolor fluorescent carbon dots (CDs) by using a series of phenols and oxidants as the precursors. The emission colors of CDs are well-controlled at blue, green, yellow or red wavelengths by adjusting the combination of a phenol and an oxidant. And the naphthalenediol with highly reactivity and the oxidant with heavy halogen atom result in CDs exhibiting long wavelength emission. The resulting nanodots are characterized as amorphous aggregates with abundant oxygen species. The phenol-derived CDs can be used as highly processible fillers to fabricate epoxy composites, and a white light-emitting diode (LED) employing the multicolor CDs/epoxy composite as the light converter is also demonstrated.

We herein report a concise process for the quantitative synthesis of polysulfates and polysulfonates through nucleophilic substitution between aryl phenols and aryl fluorosulfates in the presence of inorganic bases such as K2CO3, Na2CO3, K3PO4, Cs2CO3, etc. The reaction we developed was carried out without pre-preparation of phenolates or further modification of aryl phenols with “Si” groups (for example, TMS and TBS groups), sharply reducing the production costs both in lab research and industrial manufacture. The aryl phenolates were formed in situ, and the process was moisture and air stable. By applying this process, polysulfates and polysulfonates with the properties of high molecular weight, narrow polydispersity, kilogram scale and functional group tolerance were prepared. The byproducts of our process were water and fluorides. Several physical and chemical properties of the polymer were evaluated. Also, P-1 could be synthesized through a one-pot process in the presence of BPA, base and SO2F2. The distinct advantages of our protocol make it a more valuable mode for future industrial applications for the synthesis of polysulfates and polysulfonates, as well as the formation of sulfate bonds.

The development of techniques for monitoring the gasotransmitter carbon monoxide (CO) at the subcellular level is significant for elucidating its diverse cellular functions. Herein, a mitochondria-targetable, colorimetric and far-red fluorescent probe FR-CO is presented for tracking CO levels in the mitochondria of living cells. The FR-CO probe can sensitively detect CO using a turn-on fluorescence spectroscopic method, with a detection limit of around 38.9 nM. Additionally, the FR-CO probe exhibits outstanding selectivity towards CO over other various bioactive molecules. Moreover, the obvious color change (from colorless to pink) of the probe makes it possible to visually detect CO in aqueous solution. Most importantly, the excellent response properties of the FR-CO probe enable its application in the tracking of fluctuations in the CO levels of mitochondria in living cells, and it is thus anticipated that this probe will be a novel tool for further investigating the biological functions of CO in subcellular mitochondria.

In this study, eight 1-alkyl-2,3-dimethylimidazolium ionic liquids are analysed by X-ray photoelectron spectroscopy. The effect of both the anion and the cation on the electronic environment of cationic nitrogen regions is explored. It concludes that the cationic N 1s binding energy shifts to the lower value when the basicity of the anion increases or the acidity of the cation decreases. The impact of the cation acidity on the cation-anion interactions is demonstrated systematically by carefully comparing the binding energies of anion-based components for each anion. It is found that for more basic anions, the charge-transfer effect between counterions can be effectively shielded; for less basic anions, such an effect is negligible. The charge shielding effect of the alkyl substituent is also studied by using dodecyl-based ionic liquids, compared to 1-alkyl-3-methylimidazolium analogues. It suggests that long alkyl substituents can have a significant electron donating effect to the cation headgroup and thus effectively shield the charge-transfer effect between cations and anions.

Gate-induced ion flow through 2D layered graphene oxide membranes has been reported. The applied isolated gate voltage allows for notable control over sub-nanometer confined ionic current as a function of gate polarity and gate electrode location.

Photon enhanced thermionic emission (PETE) is a new concept in solar energy conversion, combining thermal and photovoltaic carrier excitations with thermionic emission. A solar-power-driven thermionic energy converter operates by illuminating the solar light condensed by a large-scale Fresnel lens to convert heat energy into electrical energy. By enhancing the efficiency of converting solar radiation into the emitter internal energy, the output power and efficiency of the thermionic energy converter can be greatly improved. In this study, using numerical simulations, the effects of emitter temperature and output characteristics on a thermionic energy converter were investigated. The results showed that the higher rate of the heating power represented the higher temperature of an emitter, as well as output current density, and efficiency. In addition, by reducing the diameter of a collector and thermal conductivity of insulation materials, or increasing the diameter of emitter, the temperature of emitter, output current density, and efficiency could be notably improved. It is also worth mentioning that the main factor that affected the emitter temperature in the process of heat transfer was heat conduction between solids. In conclusion, adequate illumination, reasonable size of collector and emitter, as well as appropriate insulation measurements could efficiently improve the output characteristics of thermionic energy converter.

Poor osteogenesis and implant-associated infection are the two leading causes of failure for dental and orthopedic implants. Surface design with enhanced osteogenesis often fails in antibacterial activity, or vice versa. Herein, a surface design strategy, which overcomes this trade-off via the synergistic effects of topographical micropatterning and a bilayered nanostructured metallic thin film is presented. A specific microgrooved pattern is fabricated on the titanium surface, followed by sequential deposition of a nanostructured copper (Cu)-containing tantalum (Ta) (TaCu) layer and a pure Ta cap layer. The microgrooved patterns coupled with the nanorough Ta cap layer shows strong contact guidance to preosteoblasts and significantly enhances the osteogenic differentiation in vitro, while the controlled local sustained release of Cu ions is responsible for high antibacterial activity. Importantly, rat calvarial defect models in vivo further confirm that the synergy of microgrooved patterns and the Ta|TaCu bilayered thin film on titanium surface could effectively promote bone regeneration. The present effective and versatile surface design strategy provides significant insight into intelligent surface engineering that can control biological response at the site of healing in dental and orthopedic implants.

Floquet higher order topological insulators (FHOTIs) are a novel topological phase that can occur in periodically driven lattices. An appropriate experimental platform to realize FHOTIs has not yet been identified. We introduce a periodically-driven bipartite (two-band) system that hosts FHOTI phases, and predict that this lattice can be realized in experimentally-realistic optical waveguide arrays, similar to those previously used to study anomalous Floquet insulators. The model exhibits interesting phase transitions from first-order to second-order topological matter by tuning a coupling strength parameter, without breaking lattice symmetry. In the FHOTI phase, the lattice hosts corner modes at eigenphase $0$ or $\pi$, which are robust against disorder in the individual couplings., Comment: 5+ pages for the main text, plus 7 pages for the Supplementary Materials, to be submitted to Phys. Rev. B

We present a theoretical study and experimental realization of a system that is simultaneously a four-dimensional (4D) Chern insulator and a higher-order topological insulator. The system sustains the coexistence of (4-1)-dimensional chiral topological hypersurface modes (THMs) and (4-2)-dimensional chiral topological surface modes (TSMs). Our study reveals that the THMs are protected by second Chern numbers, and the TSMs are protected by a topological invariant composed of two first Chern numbers, each belonging to a Chern insulator existing in subdimensions. With the synthetic coordinates fixed, the THMs and TSMs, respectively, manifest as topological edge modes and topological corner modes (TCMs) in the real space, which are experimentally observed in a 2D acoustic lattice. These TCMs are not related to quantized polarizations, making them fundamentally distinctive from existing examples. We further show that our 4D topological system offers an effective way for the manipulation of the frequency, location, and number of TCMs, which is highly desirable for applications.

We report three new FRBs discovered by the Five-hundred-meter Aperture Spherical radio Telescope (FAST), namely FRB 181017.J0036+11, FRB 181118 and FRB 181130, through the Commensal Radio Astronomy FAST Survey (CRAFTS). Together with FRB 181123 that was reported earlier, all four FAST-discovered FRBs share the same characteristics of low fluence ($\leq$0.2 Jy ms) and high dispersion measure (DM, $>1000$ \dmu), consistent with the anti-correlation between DM and fluence of the entire FRB population. FRB 181118 and FRB 181130 exhibit band-limited features. FRB 181130 is prominently scattered ($��_s\simeq8$ ms) at 1.25 GHz. FRB 181017.J0036+11 has full-bandwidth emission with a fluence of 0.042 Jy ms, which is one of the faintest FRB sources detected so far. CRAFTS starts to built a new sample of FRBs that fills the region for more distant and fainter FRBs in the fluence-$\rm DM_E$ diagram, previously out of reach of other surveys. The implied all sky event rate of FRBs is $1.24^{+1.94}_{-0.90} \times 10^5$ sky$^{-1}$ day$^{-1}$ at the $95\%$ confidence interval above 0.0146 Jy ms. We also demonstrate here that the probability density function of CRAFTS FRB detections is sensitive to the assumed intrinsic FRB luminosity function and cosmological evolution, which may be further constrained with more discoveries., 9 Pages, 4 Plots and 1 Table. The Astrophysical Journal Letter Accepted

When galaxies merge, the supermassive black holes in their centers may form binaries and emit low-frequency gravitational radiation in the process. In this paper, we consider the galaxy 3C 66B, which was used as the target of the first multimessenger search for gravitational waves. Due to the observed periodicities present in the photometric and astrometric data of the source, it has been theorized to contain a supermassive black hole binary. Its apparent 1.05-year orbital period would place the gravitational-wave emission directly in the pulsar timing band. Since the first pulsar timing array study of 3C 66B, revised models of the source have been published, and timing array sensitivities and techniques have improved dramatically. With these advances, we further constrain the chirp mass of the potential supermassive black hole binary in 3C 66B to less than (1.65 ± 0.02) × 109 M ⊙ using data from the NANOGrav 11-year data set. This upper limit provides a factor of 1.6 improvement over previous limits and a factor of 4.3 over the first search done. Nevertheless, the most recent orbital model for the source is still consistent with our limit from pulsar timing array data. In addition, we are able to quantify the improvement made by the inclusion of source properties gleaned from electromagnetic data over “blind” pulsar timing array searches. With these methods, it is apparent that it is not necessary to obtain exact a priori knowledge of the period of a binary to gain meaningful astrophysical inferences.

Self-assembled virus-like particles (VLPs) hold great potential as natural nanomaterials for applications in many fields. For such purposes, monodisperse size distribution is a desirable property. However, the VLPs of simian virus 40 (SV40), a representative VLP platform, are characterized by polymorphism. In an attempt to eliminate the polymorphism, 15 mutants of the VLP subunit (VP1) are constructed through the substitution of double cysteines at the VP1 pentamer interfaces, generating a group of VLPs with altered size distributions. One of the mutants, SS2 (L102C/P300C), specifically forms homogenous T = 1-like tiny VLPs of 24 ± 3 nm in diameter. Moreover, the stability of the SS2 VLPs is markedly enhanced compared with that of wild-type VLPs. The homogeneous self-assembly and stability enhancement of SS2 VLPs can be attributed to the new disulfide bonds contributed by Cys102 and Cys300, which are identified by mass spectrometry and explored by molecular dynamics simulations. Endocytosis inhibition assays indicate that SS2 VLPs, like the polymorphic wild-type VLPs, preserve the multipathway feature of cellular uptake. SS2 VLPs may serve as an evolved version of SV40 VLPs in future studies and applications. The findings of this work would be useful for the design and fabrication of VLP-based materials and devices.

We present timing solutions and analyses of 11 pulsars discovered by the Five-hundred-meter Aperture Spherical radio Telescope (FAST). These pulsars were discovered using an ultra-wide bandwidth receiver in drift-scan observations made during the commissioning phase of FAST, and were then confirmed and timed using the 64-m Parkes Radio Telescope. Each pulsar has been observed over a span of at least one year. Highlighted discoveries include PSR J0344-0901, which displays mode-changing behaviour and may belong to the class of so-called `swooshing' pulsars (alongside PSRs B0919+06 and B1859+07); PSR J0803-0942, whose emission is almost completely linearly polarised; and PSRs J1900-0134 and J1945+1211, whose well defined polarisation angle curves place stringent constraints on their emission geometry. We further discuss the detectability of these pulsars by earlier surveys, and highlight lessons learned from our work in carrying out confirmation and monitoring observations of pulsars discovered by a highly sensitive telescope, many of which may be applicable to next-generation pulsar surveys. This paper marks one of the first major releases of FAST-discovered pulsars, and paves the way for future discoveries anticipated from the Commensal Radio Astronomy FAST Survey (CRAFTS)., 18 pages, 8 figures, 5 tables. Accepted for publication by MNRAS. Correcting error in the caption of Figure 8

The exotic topological states have advanced the exploration for topological characteristics, such as invariant topological orders and band inversion. Here, we experimentally construct photonic dimer chains composed of split-ring resonators to exhibit interesting topological properties with different orientation angles. By using the method of near-field detection, we measure the dispersion relation and sublattice pseudospin vectors of different orientated configurations, which immediately determines the associated winding number of bulk bands as the topological invariant. Moreover, the sublattice pseudospin vector inversion observed at band edges indicates the band inversion and the associated topological phase transition, which is reconfirmed by measuring the band-edge mode parity and symmetry of the split-ring resonator cell. Our results not only directly show the topological winding number, band inversion, pseudospin, and the symmetries of band-edge states in experiments, but also reveal the great potential of the split-ring resonator platform to experimentally explore the advanced topological characteristics, such as higher winding numbers or higher Chern numbers in more complex setups.

Topological corner modes (TCMs) can exist in two-dimensional square lattices with either quantized dipole moments or a quantized bulk quadrupole moment. In both cases, four TCMs, each localized at one corner, can be found degenerate at zero energy. Here, we analytically show that in finite-sized systems, adjacent TCMs can couple, with hopping strength and sign determined by the edge configuration, which is directly associated with the magnetic flux of the unit cell. Consequently, we found that the response functions of the coupled corner modes of different origins, i.e., quantized edge dipoles and a quantized bulk quadrupole, possess distinctive line shapes. The response functions can therefore be used as a hallmark to determine the corner modes' nature. We verify our findings in simulations using phononic crystals.

We report the discovery of an eclipsing binary millisecond pulsar in the globular cluster M92 (NGC6341) with the Five-hundred-meter Aperture Spherical radio Telescope (FAST). PSR J1717+4308A, or M92A, has a pulse frequency of 316.5~Hz (3.16~ms) and a dispersion measure of 35.45 pc cm$^{-3}$. The pulsar is a member of a binary system with an orbital period of 0.20~days around a low-mass companion which has a median mass of $\sim$0.18~\Ms. From observations so far, at least two eclipsing events have been observed in each orbit. The longer one lasted for ~5000~s in the orbital phase range 0.1--0.5. The other lasted for ~500~s and occurred between 1000--2000~s before or after the longer eclipsing event. The lengths of these two eclipsing events also change. These properties suggest that J1717+4308A is a ``red-back'' system with a low-mass main sequence or sub-giant companion. Timing observations of the pulsar and further searches of the data for additional pulsars are ongoing., 9 pages, 2 figures, submitted to ApJL, comments are welcomed!

We present a new analysis of the profile data from the 47 millisecond pulsars comprising the 12.5-year data set of the North American Nanohertz Observatory for Gravitational Waves (NANOGrav), which is presented in a parallel paper (Alam et al. 2021a; NG12.5). Our reprocessing is performed using "wideband" timing methods, which use frequency-dependent template profiles, simultaneous time-of-arrival (TOA) and dispersion measure (DM) measurements from broadband observations, and novel analysis techniques. In particular, the wideband DM measurements are used to constrain the DM portion of the timing model. We compare the ensemble timing results to NG12.5 by examining the timing residuals, timing models, and noise model components. There is a remarkable level of agreement across all metrics considered. Our best-timed pulsars produce encouragingly similar results to those from NG12.5. In certain cases, such as high-DM pulsars with profile broadening, or sources that are weak and scintillating, wideband timing techniques prove to be beneficial, leading to more precise timing model parameters by 10-15%. The high-precision, multi-band measurements of several pulsars indicate frequency-dependent DMs. Compared to the narrowband analysis in NG12.5, the TOA volume is reduced by a factor of 33, which may ultimately facilitate computational speed-ups for complex pulsar timing array analyses. This first wideband pulsar timing data set is a stepping stone, and its consistent results with NG12.5 assure us that such data sets are appropriate for gravitational wave analyses., Comment: 62 pages, 55 figures, 5 tables, 3 appendices. Data available at http://nanograv.org/data/ and via DOI 10.5281/zenodo.4312887

We report the discovery of a highly dispersed fast radio burst, FRB~181123, from an analysis of $\sim$1500~hr of drift-scan survey data taken using the Five-hundred-meter Aperture Spherical radio Telescope (FAST). The pulse has three distinct emission components, which vary with frequency across our 1.0--1.5~GHz observing band. We measure the peak flux density to be $>0.065$~Jy and the corresponding fluence $>0.2$~Jy~ms. Based on the observed dispersion measure of 1812~cm$^{-3}$~pc, we infer a redshift of $\sim 1.9$. From this, we estimate the peak luminosity and isotropic energy to be $\lesssim 2\times10^{43}$~erg~s$^{-1}$ and $\lesssim 2\times10^{40}$~erg, respectively. With only one FRB from the survey detected so far, our constraints on the event rate are limited. We derive a 95\% confidence lower limit for the event rate of 900 FRBs per day for FRBs with fluences $>0.025$~Jy~ms. We performed follow-up observations of the source with FAST for four hours and have not found a repeated burst. We discuss the implications of this discovery for our understanding of the physical mechanisms of FRBs., 7 pages, 3 figures, accepted for publication in ApJL

To investigate the use of saliency-map analysis to aid in searches for transient signals, such as fast radio bursts and individual pulses from radio pulsars. We aim to demonstrate that saliency maps provide the means to understand predictions from machine learning algorithms and can be implemented in piplines used to search for transient events. We have implemented a new deep learning methodology to predict whether or not any segment of the data contains a transient event. The algorithm has been trained using real and simulated data sets. We demonstrate that the algorithm is able to identify such events. The output results are visually analysed via the use of saliency maps. We find that saliency maps can produce an enhanced image of any transient feature without the need for de-dispersion or removal of radio frequency interference. Such maps can be used to understand which features in the image were used in making the machine learning decision and to visualise the transient event. Even though the algorithm reported here was developed to demonstrate saliency-map analysis, we have detected, in archival data, a single burst event with dispersion measure of $41$\,cm$^{-3}$pc that is not associated with any currently known pulsar., Comment: 16 pages, 6 figures, accepted for publication in A&A

Using data from the Large European Array for Pulsars (LEAP), and the Effelsberg telescope, we study the scintillation parameters of the millisecond pulsar J0613-0200 over a 7 year timespan. The "secondary spectrum" -- the 2D power spectrum of scintillation -- presents the scattered power as a function of time delay, and contains the relative velocities of the pulsar, observer, and scattering material. We detect a persistent parabolic scintillation arc, suggesting scattering is dominated by a thin, anisotropic region. The scattering is poorly described by a simple exponential tail, with excess power at high delays; we measure significant, detectable scattered power at times out to $\sim 5 \mu s$, and measure the bulk scattering delay to be between 50 to 200\,ns with particularly strong scattering throughout 2013. These delays are too small to detect a change of the pulse profile shape, yet they would change the times-of-arrival as measured through pulsar timing. The arc curvature varies annually, and is well fit by a one-dimensional scattering screen $\sim 40\%$ of the way towards the pulsar, with a changing orientation during the increased scattering in 2013. Effects of uncorrected scattering will introduce time delays correlated over time in individual pulsars, and may need to be considered in gravitational wave analyses. Pulsar timing programs would benefit from simultaneously recording in a way that scintillation can be resolved, in order to monitor the variable time delays caused by multipath propagation., Comment: 12 pages, 10 figures. Published in MNRAS

Full list of authors: Lin, L.; Zhang, C. F.; Wang, P.; Gao, H.; Guan, X.; Han, J. L.; Jiang, J. C.; Jiang, P.; Lee, K. J.; Li, D.; Men, Y. P.; Miao, C. C.; Niu, C. H.; Niu, J. R.; Sun, C.; Wang, B. J.; Wang, Z. L.; Xu, H.; Xu, J. L.; Xu, J. W.; Yang, Y. H.; Yang, Y. P.; Yu, W.; Zhang, B.; Zhang, B. -B.; Zhou, D. J.; Zhu, W. W.; Castro-Tirado, A. J.; Dai, Z. G.; Ge, M. Y.; Hu, Y. D.; Li, C. K.; Li, Y.; Li, Z.; Liang, E. W.; Jia, S. M.; Querel, R.; Shao, L.; Wang, F. Y.; Wang, X. G.; Wu, X. F.; Xiong, S. L.; Xu, R. X.; Yang, Y. -S.; Zhang, G. Q.; Zhang, S. N.; Zheng, T. C.; Zou, J. -H., Fast radio bursts (FRBs) are millisecond-duration radio transients of unknown physical origin observed at extragalactic distances1–3. It has long been speculated that magnetars are the engine powering repeating bursts from FRB sources4–13, but no convincing evidence has been collected so far14. Recently, the Galactic magnetar SRG 1935+2154 entered an active phase by emitting intense soft γ-ray bursts15. 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 flare18–21. 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. © 2020, The Author(s), under exclusive licence to Springer Nature Limited., This work is supported by the Natural Science Foundation of China (grants 11988101, 11673002, 11703002, 11543004, 11722324, 11690024, 11633001, 11920101003, 11833003, 11722324, 11633001, 11690024, 11573014, 11725314, 11690024, 11743002, 11873067, 11533003, 11673006, U1938201, 11725313, 11721303, 1172130, U15311243, U1831207, U1838201, U1838202, U1838113, U1938109), National Key Research and Development Programs of China (grants 2018YFA0404204, 2017YFA0402600), the Program for Innovative Talents and Entrepreneur in Jiangsu, the KIAA-CAS Fellowship, the China Postdoctoral Science Foundation (grants 2018M631242, 2016YFA0400800, 2018YFA0400802, E01S11BQ10, XDB23010200,XDB2304040, QYZDY-SSW-SLH008), the International Partnership Program of Chinese Academy of Sciences (grant number 114A11KYSB20160008), the Cultivation Project for FAST Scientific Payoff and Research Achievement of CAMS-CAS, the Max-Planck Partner Group, the Spanish Science Ministry “Centro de Excelencia Severo Ochoa” Program (grant SEV-2017-0709), the Junta de Andalucía (Project P07-TIC-03094) and the Spanish Ministry Projects AYA2012-39727-C03-01, AYA2015-71718R and PID2019-109974RB-I00. We thank E. Fernández-García (IAA-CSIC), I. M. Carrasco-García and C. Pérez del Pulgar (UMA) and the rest of the BOOTES Team for making the reported BOOTES Network observations possible. This work made use of data from FAST—a Chinese national mega-science facility, built and operated by the National Astronomical Observatories, Chinese Academy of Sciences. We also acknowledge the use of public data from the Fermi Science Support Center (FSSC).