Search

The nearby radio galaxy M87 is a very high-energy (VHE) gamma-ray emitter established by observations with ground-based gamma-ray detectors. Here we report the long-term monitoring of M87 from 2021 to 2024 with the Large High Altitude Air Shower Observatory (LHAASO). M87 has been detected by LHAASO with a statistical significance ∼ 9 σ . The observed energy spectrum extends to 20 TeV, with a possible hardening at ∼20 TeV and then a clear softening at higher energies. Assuming that the intrinsic spectrum is described by a single power law up to 20 TeV, a tight upper bound on the extragalactic background light intensity is obtained. A strong VHE flare lasting 8 days, with a rise time of ${\tau }_{r}^{\mathrm{rise}}=1.05\pm 0.49$ days and decay time of ${\tau }_{d}^{\mathrm{decay}}=2.17\pm 0.58$ days, was found in early 2022. A possible GeV flare is seen also in Fermi Large Area Telescope data during the VHE flare period. The variability time as short as 1 day seen in the LHAASO data suggests a compact emission region with a size of ∼3 × 10 ^15 δ cm ( δ being the Doppler factor of the emitting region), corresponding to a few Schwarzschild radii of the central supermassive black hole in M87. The continuous monitoring of the source reveals a duty cycle of ∼1% for VHE flares with a flux above 10 ^−11 erg cm ^−2 s ^−1 .

The first source catalog of the Large High Altitude Air Shower Observatory (LHAASO) reported the detection of a very high energy gamma-ray source, 1LHAASO J1219+2915. This Letter presents a further detailed study of the spectral and temporal behavior of this pointlike source. The best-fit position of the TeV source (R.A. = 185.°05 ± 0.°04, decl. = 29.°25 ± 0.°03) is compatible with NGC 4278 within ∼0.°03. Variation analysis shows an indication of variability on a timescale of a few months in the TeV band, which is consistent with low-frequency observations. Based on these observations, we report the detection of TeV γ -ray emissions from this low-luminosity active galactic nucleus. The observation by LHAASO's Water Cherenkov Detector Array during the active period has a significance level of 8.8 σ with a best-fit photon spectral index Γ = 2.56 ± 0.14 and a flux f _1–10 TeV = (7.0 ± 1.1 _sta ± 0.35 _syst ) × 10 ^−13 photons cm ^−2 s ^−1 , or approximately 5% of the Crab Nebula. The discovery of VHE gamma-ray emission from NGC 4278 indicates that compact, weak radio jets can efficiently accelerate particles and emit TeV photons.

We present periodicity search analyses on the long-term γ -ray light curve of the BL Lacertae object 4FGL J2139.4−4235 observed by the Fermi Large Area Telescope, over a period of more than 15 yr, from 2008 August 4 to 2023 December 10. To determine the quasiperiodic oscillation (QPO) behavior of 4FGL J2139.4−4235 in the 0.3–300 GeV energy range, we used four methods, namely the Lomb–Scargle periodogram, the weighted wavelet z-transform, the phase dispersion minimization, and the autoregressive integrated moving average model. A Monte Carlo simulation technique is used to evaluate the significance level of the QPO signal. Significant levels above 3.5 σ were detected in the γ -ray light curve at about 650 days QPO, which is presented throughout the observation period. Interestingly, there was some correlation between the three bands in the discrete correlation function method calculations, which may be an indication that the variability trends between the three bands are similar. We explore the possible physical models and show that a supermassive binary black hole system or a jet helical motion model seem to be reasonable explanations for the potential QPO behavior.

Flexible electronics have attracted extensive attention across a wide range of fields due to their potential for preventive medicine and early disease detection. Microfiber-based textiles, encountered in everyday life, have emerged as promising platforms with integrated sensing capabilities. Microfluidic technology has been recognized as a promising avenue for the development of flexible conductive microfibers and has made significant achievements. In this review, we provide a comprehensive overview of the state-of-the-art advancements in microfiber-based flexible electronics fabricated using microfluidic platforms. Firstly, the fundamental strategies of the microfluidic fabrication of conductive microfibers with different structures and morphologies are introduced. Subsequently, attention is then directed towards the diverse applications of these microfibers in bioelectronics. Finally, we offer a forward-looking perspective on the future challenges about microfluidic-derived microfibers in flexible bioelectronics.

This study presents detailed time-integrated and time-resolved spectral analysis of the Fermi Gamma-ray Burst Monitor observations of the bright GRB 231129C. The results reveal its distinct spectral characteristics, featuring a hard low-energy spectral index ( α ) and soft high-energy spectral index ( β ), similar to GRB 090902B, suggesting a possible dominance of thermal emission. Further analysis indicates that 92% of the spectral indices exceed the synchrotron “line of death,” with the hardest index at α ∼ +0.44. Simultaneously, 53% of the spectra can be well fitted by the nondissipative photosphere model, supporting a potential origin from a nondissipative photosphere. Additionally, we observe strong correlations between the spectral index α and peak energy E _p with flux. For the α − F relationship, we employ F = F _0 e ^(3.00±0.10) ^α to describe it, whereas the E _p − F relationship requires a smoothly bending power-law function. Based on the framework proposed by Hascoët et al. and Gao & Zhang, the jet characteristics of this burst were studied, revealing that both methods support the suitability of a pure fireball model for this GRB at small initial jet radii.

Topological photonics offers a powerful platform for next-generation nanophotonic chips, capitalizing on their remarkable resilience to disorder and defects. Among the two-dimensional (2D) photonic topological insulators, valley-Hall (VH) and pseudo-spin-Hall (PSH) topological insulators have emerged as the most practical designs, as they do not require breaking time-reversal symmetry. These photonic topological insulators support robust edge states, demonstrating promising potential for a wide range of applications, from on-chip communication to optical computing and sensing. However, the conversion between distinct topological phases (VH and PSH) in terahertz (THz) band has not been achieved. Here we experimentally demonstrate a THz on-chip spin–valley converter through adiabatic evolution in 2D parameter space without closing the bulk bandgap. By leveraging the adiabatic phase transition, we confirm the high-efficiency conversion between two valley states in a valley–spin–valley converter. In addition, we verify the robustness of THz PSH topological energy transport through sharply twisted corners. Our findings not only advance the understanding of topological phases in photonics but also hold promise for the development of innovative photonic devices with enhanced performance and functionality.

Patterns of the Indian Ocean Dipole (IOD) exhibit strong diversity, ranging from being dominated by the western tropical Indian ocean (WTIO) to by the eastern tropical Indian ocean. How the different types of the IOD variability patterns affect Australian fires differently is unknown, nor is it certain how the impacts may change under greenhouse warming. Here, we find that the moderate IOD, dominated by WTIO sea surface temperature (SST) variability, plays a primary role in affecting southern Australian fire weather conditions during austral spring. During a positive moderate IOD, broad-scaled warm SST anomalies in WTIO force an atmospheric stationary Rossby wave with a high-pressure anomaly over southern Australia. This elevated pressure and associated anomalous atmospheric conditions provide suitable fire weather with hot, dry, and windy conditions, raising fire risks in southern Australia. Such impact is distinctively different from that strong IOD-induced. As predicted by climate models, decreased moderate IOD variability in the future will result in weakened Australian fire weather responses.

Pulsar wind nebula HESS J1849-000 is one of the sources that may emit PeV γ -ray photons based on the recent measurement by the Tibet Air Shower Array and the Large High Altitude Air Shower Observatory. We use a time-dependent model to investigate the nonthermal radiative properties of HESS J1849-000. Observed multiband data are produced well by relativistic leptons through synchrotron radiation and inverse Compton processes, and the particle transport and cooling processes are analyzed. Our results show that the particle adiabatic loss dominates over the synchrotron loss and inverse Compton losses, and the particle advection dominates over diffusion for the low-energy band. On the other hand, the particle synchrotron loss dominates over the adiabatic loss and inverse Compton losses, and the diffusion dominates over advection for the high-energy band. Furthermore, particle transport would be playing a significant role in the low-energy band, whereas the particle cooling processes may play a more important role in the high-energy band. The current diffusion coefficient 3.4 × 10 ^26 cm ^2 s ^−1 at an electron energy of 1 TeV is derived, which implies a slow diffusion mechanism may occur within the nebula. More importantly, our model suggests that the particle's maximum energy is 3.6 PeV, which makes HESS J1849-000 a PeVatron candidate.

We present the first catalog of very-high-energy and ultra-high-energy gamma-ray sources detected by the Large High Altitude Air Shower Observatory. The catalog was compiled using 508 days of data collected by the Water Cherenkov Detector Array from 2021 March to 2022 September and 933 days of data recorded by the Kilometer Squared Array from 2020 January to 2022 September. This catalog represents the main result from the most sensitive large coverage gamma-ray survey of the sky above 1 TeV, covering decl. from −20° to 80°. In total, the catalog contains 90 sources with an extended size smaller than 2° and a significance of detection at >5 σ . Based on our source association criteria, 32 new TeV sources are proposed in this study. Among the 90 sources, 43 sources are detected with ultra-high energy ( E > 100 TeV) emission at >4 σ significance level. We provide the position, extension, and spectral characteristics of all the sources in this catalog.

As a new member of the Gravitational-wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) after GECAM-A and GECAM-B, GECAM-C (originally called HEBS), which was launched on board the SATech-01 satellite on 2022 July 27, aims to monitor and localize X-ray and gamma-ray transients from ∼6 keV to 6 MeV. GECAM-C utilizes a similar design to GECAM but operates in a more complex orbital environment. In this work, we utilize the secondary particles simultaneously produced by the cosmic-ray events on orbit and recorded by multiple detectors to calibrate the relative timing accuracy between all detectors of GECAM-C. We find the result is 0.1 μ s, which is the highest time resolution among all GRB detectors ever flown and very helpful in timing analyses such as minimum variable timescale and spectral lags, as well as in time delay localization. Besides this, we calibrate the absolute time accuracy using the one-year Crab Pulsar data observed by GECAM-C and Fermi’s Gamma-ray Burst Monitor, as well as GECAM-C and GECAM-B. The results are 2.02 ± 2.26 μ s and 5.82 ± 3.59 μ s, respectively. Finally, we investigate the spectral lag between the different energy bands of the Crab Pulsar observed by GECAM and the Gamma-ray Burst Monitor, which is ∼ −0.2 μ s keV ^−1 .

We analyzed the influence of outflow feedback from two perspectives: turbulent support and potential disruptive effect, of which 694 clumps and 188 have been identified as outflow candidates. For turbulent support, we find the slopes of E _turb − R _clump (turbulent energy and radius of the clump) and P _turb − R _clump (turbulent momentum and radius of the clump) have no difference and are consistent with expected values whether there is outflow feedback in clumps or not. The ratios of the outflow energy and momentum to the turbulence energy and momentum ( E _flow / E _turb , P _flow / P _turb ) show that the majority of clumps have not enough energy and momentum to support turbulence. Meanwhile, there is no correlation between the velocity dispersion and radius. For potential disruptive effects, we conclude that it is impossible for the outflow activities to disrupt entire clumps and as the mass of the clumps increases, the clumps becomes harder to destroy. Finally, we do not see evidence that the virial parameter changes significantly whether the clumps have outflow candidates or not.

A turbulent diffusion model is presented to account for the energy and spatial diffusion of the particles within pulsar wind nebulae (PWNe), with the assumption that the energy injected from the pulsar into the nebula is split between the turbulence waves and electrons/positrons. In the model, the mutual interactions between the turbulence waves and particles are taken into account, representing the damping effect of the turbulence waves and the stochastic acceleration and spatial diffusion of the particles, respectively. The evolutions of the turbulence waves and particles are described with the coupled kinetic equations, in which the Kolmogorov- and Kraichnan-type turbulence are, respectively, considered. The model is applied to the Crab Nebula and shows that the spectral energy distribution of the PWN can be naturally explained. Our modeling results indicate that, for the Crab Nebula, the stochastic acceleration and spatial diffusion processes play a role in modifying the electron spectrum at the low energies of E _e ≲ 1 TeV. The damping process seems more effective for modulating the turbulent spectrum in the Kraichnan-type turbulence, resulting in the nonlinear variations of the current energy and spatial diffusion coefficients with energy generated in the wave–particle systems. In the Kolmogorov-type turbulence, the diffusion coefficients are more consistent with the quasi-linear distributions, due to the energy cascade dominating over the damping effect.

We uncover the interaction-induced stable self-localization of few bosons in finite-size disorder-free superlattices. In these nonthermalized multi-particle states, one of the particles forms a superposition of multiple standing waves, so that it provides a quasi-random potential to localize the other particles. We derive effective Hamiltonians for self-localized states and find their energy level spacings obeying the Poisson statistics. The spatial distribution of the localized particles decays exponentially, which is refered to Anderson-like localization (ALL). Surprisingly, we find that the correlated self-localization can be solely induced by interaction in the well-studied Bose–Hubbard models, which has been overlooked for a long time. We propose a dynamical scheme to detect self-localization, where long-time quantum walks of a single particle form a superposition of multiple standing waves for trapping the subsequently loaded particles. Our work provides an experimentally feasible way to realize stable ALL in translation-invariant disorder-free few-body systems.

We present observations of the rapid decay of a penumbral sector associated with a strong light bridge (LB) in the active region NOAA 12680 by analyzing the scattered light-corrected Solar Dynamics Observatory/Helioseismic and Magnetic Imager data. At the beginning of penumbral decay, some dark structures gradually broke away from the umbra to which they were attached. The intensity, vertical field strength, and magnetic inclination of the dark structures are intermediate between those of the umbra and penumbra. And a strong LB formed in the umbra, which originated from the intrusion of neighboring penumbral filaments. With the formation of an LB, the total magnetic flux in the whole penumbra decreased, and a penumbral sector of the sunspot rapidly disappeared on one side of the LB. After performing a partition analysis of the penumbra, it was found that the decay rate in this region of the penumbral sector is significantly accelerated after the appearance of an outward motion of magnetic flux along the LB. The area of this penumbral sector decreased from 21–16 MSH in 4 hr. The reduction in area in this penumbral sector is accompanied by a large decay rate of the magnetic flux, 2.5 × 10 ^19 Mx hr ^−1 . These results suggest that the rapid decay of the penumbral sector is associated with the LB. The appearance of dark structures in the penumbra and the strong LB in the umbra may offer a hint that the origin of massive flux migration from the sunspot umbra may have accelerated the decay of the sunspot.

The broadband emission of numerous pulsar wind nebula (PWNe) in our Galaxy can be well described by synchrotron radiation and inverse Compton scattering from relativistic particles, specifically electrons and positrons. However, the particle transport mechanism is still under debate. We use here a time-dependent model to investigate the particle transport process of the young PWN, while the particle cooling processes are also analyzed. Following applications of the model to six young PWNe, our results show that (1) the particle cooling process is dominated by adiabatic loss in the low-energy band but by synchrotron loss in the high-energy band; (2) the advection dominates the particle transport process in the low-energy band, whereas the advection and diffusion codominate in the high-energy band, indicating that both advection and diffusion play an important role in particle transport; and (3) the diffusion coefficient is (2–360) × 10 ^24 cm ^2 s ^−1 at the electron energy of 1 TeV, i.e., about 3 orders of magnitude smaller than the value considered to be the average in the Galaxy. We conclude that a slow-diffusion mechanism may explain the multiband observation of the sample of six young PWNe considered in this study.

Blazar jet structure can be indirectly resolved by analyzing the multiwavelength variability. In this work, we analyze the long-term variability of blazars in radio, optical, and X-ray energies with the Gaussian process (GP) method. The multiwavelength variability can be successfully characterized by the damped-random walk model. The nonthermal optical characteristic timescales of 38 blazars are statistically consistent with the γ -ray characteristic timescales of 22 blazars. For three individual sources (3C 273, PKS 1510-089, and BL Lac), the nonthermal optical, X-ray, and γ -ray characteristic timescales are also consistent within the measured 95% errors, but the radio timescale of 3C 273 is too large to be constrained by the decade-long light curve. The synchrotron and inverse-Compton emissions have the same power spectral density, suggesting that the long-term jet variability is irrelevant to the emission mechanism. In the plot of the rest-frame timescale versus black hole mass, the optical- γ -ray timescales of the jet variability occupy almost the same space with the timescales of accretion disk emission from normal quasars, which may imply that the long-term variabilities of the jet and accretion disk are driven by the same physical process. It is suggested that the nonthermal optical-X-ray and γ -ray emissions are produced in the same region, while the radio core, which can be resolved by very long baseline interferometry, locates at a far more distant region from the black hole. Our study suggests a new methodology for comparing thermal and nonthermal emissions, which is achieved by using the standard GP method.

Port cities in Southeast Asia (SEA) have been undergoing intensive land use and land cover change (LUCC) because of rapid socio-economic development in recent decades. However, various development statuses among these cities could result in divergent LUCC transitions and therefore affect the local ecosystem at different levels. This study investigated the historic land-use transition in the SEA port cities by classifying Landsat images from 1990 to 2020 with the random forest algorithm, and further integrated these patterns with land-use modeling to inform the future land uses under the current developing mode. DIVISON was used to assess land-use fragmentation and investigated its relationship with development levels represented by the average nighttime light index (ANLI). The results showed an intensive LUCC in SEA port cities in 1990–2020, with artificial surface increasing by 9.2% (175.9 km ^2 ) of the total area, mainly converted from cultivated land which decreased by 136.9 km ^2 . An inverted V-shaped relationship between fragmentation and development level was found at the landscape level and for cultivated land, in which both turning points (TPs) occurred in the mid-developed stage (ANLI = 41.1 and 20.0, respectively). Artificial surfaces tended to be more aggregated in later developed stages, showing a TP of ANLI around 53.2. Under the current developing mode, the aggregation trend will be generally continued for the next three decades, mainly resulting from the increased connection in artificial surfaces. The findings also highlighted a tradeoff between city development and agricultural production in SEA port cities, leading to increased food insecurity in more developed stages. Recent developments also negatively affected aqua ecosystems, such as aquaculture, mangroves, and natural waterbodies in several cities. This study underscored the importance of the sustainable LUCC strategy in SEA port cities and provides insights into rationalizing land-use policies for other port cities worldwide.

The warm Arctic-cold Eurasia (WACE) pattern of surface air temperature anomalies is a prominent feature of the Eurasian climate variations during boreal winter. The interannual WACE anomalies are accompanied by sea ice loss in the Barents-Kara (BK) seas, however, the causality between them remains controversial because of large internal atmospheric variability over subarctic Eurasia in winter. Here we disentangle the contribution of BK sea ice loss to the WACE anomalies based on a statistical decomposition approach. An anticyclonic circulation anomaly over subarctic Eurasia that forces the WACE anomalies is found to reach its peak 3 d prior to BK sea ice loss. After excluding this prior atmospheric forcing signature, the East Asian cooling matures about 15 d later as a result of the weakened moisture transport associated with the enhanced BK downstream ridge and East Asian trough due to BK sea ice loss. The results suggest that BK sea ice loss contributes ∼65% and ∼81% of the WACE-related East Asian cooling and Arctic warming at interannual timescale, respectively, whereas the WACE-related cooling over central Eurasia primarily results from internal atmospheric variability. Such submonthly lagged East Asia cooling caused by BK sea ice loss could be helpful in predicting winter extreme cold events over East Asia.

The Gravitational Wave High-energy Electromagnetic Counterpart All-sky Monitor (GECAM) is a pair of microsatellites (i.e., GECAM-A and GECAM-B) dedicated to monitoring gamma-ray transients including the high-energy electromagnetic counterparts of gravitational waves, such as gamma-ray bursts, soft gamma-ray repeaters, solar flares, and terrestrial gamma-ray flashes. Since launch in 2020 December, GECAM-B has detected hundreds of astronomical and terrestrial events. For these bursts, localization is the key for burst identification and classification as well as follow-up observations in multiple wavelengths. Here, we propose a Bayesian localization method with Poisson data with Gaussian background profile likelihood to localize GECAM bursts based on the distribution of burst counts in detectors with different orientations. We demonstrate that this method can work well for all kinds of bursts, especially extremely short ones. In addition, we propose a new method to estimate the systematic error of localization based on a confidence level test, which can overcome some problems of the existing method in the literature. We validate this method by Monte Carlo simulations, and then apply it to a burst sample with accurate location and find that the mean value of the systematic error of GECAM-B localization is ∼2.°5. By considering this systematic error, we can obtain a reliable localization probability map for GECAM bursts. Our methods can be applied to other gamma-ray monitors.

As components of terrestrial carbon sinks, vegetation and soil carbon pools are important for offsetting CO _2 emissions. However, differences in their carbon sequestration capacities and their responses to global change in the future are poorly understood. This study assessed the changes in vegetation and soil carbon and their ratios and drivers under the SSP126 scenario from 2015 to 2060, using Coupled Model Intercomparison Project phase 6 simulations in China, a major carbon sink region in global terrestrial ecosystems. The content of vegetation carbon (29 ± 1 PgC) was observed to be lower than that of soil carbon (113 ± 23 PgC), and the ratio of vegetation to soil carbon was the highest in the subtropical-tropical monsoon climatic region (0.55 ± 0.12). Moreover, the total stock of vegetation and soil carbon increased by 10 ± 1 PgC during the study period, and the increase in vegetation carbon was 4.31 times that of soil carbon, because the responses of vegetation carbon stocks to increased forest coverage and atmospheric CO _2 were greater than that of soil carbon stocks, especially in the subtropical-tropical and temperate monsoonal climatic regions. However, bare land encroachment on grasslands reduced their increments in the temperate monsoonal and high-cold Tibetan Plateau climatic regions. Furthermore, compared with SSP245 and SSP585 scenarios, vegetation and soil carbon sinks can offset a greater amount of carbon emissions in 2060 under the SSP126 scenario, accounting for 53% of all carbon emissions, offsetting 60%–79% of carbon emissions from China under its policy of increasing forest coverage. The study revealed the important role of afforestation in increasing ecosystem carbon stocks, additionally, grassland conservation and deep reductions in carbon emissions cannot be ignored in the future. This study provides a basis for determining the response of vegetation and soil carbon to environmental factors and the realization of net-zero emissions globally.

Antarctic sea ice plays an important role in polar ecosystems and global climate, while its variability is affected by many factors. Teleconnections between the tropical and high latitudes have profound impacts on Antarctic climate changes through the stationary Rossby wave mechanism. Recent studies have connected long-term Antarctic sea ice changes to multidecadal variabilities of the tropical ocean, including the Atlantic Multidecadal Oscillation and the Interdecadal Pacific Oscillation. On interannual timescales, whether an impact exists from teleconnection of the tropical Atlantic is not clear. Here we find an impact of sea surface temperature (SST) variability of the tropical Atlantic meridional dipole mode on Antarctic sea ice that is most prominent in austral autumn. The meridional dipole SST anomalies in the tropical Atlantic force deep convection anomalies locally and over the tropical Pacific, generating stationary Rossby wave trains propagating eastward and poleward, which induce atmospheric circulation anomalies affecting sea ice. Specifically, convective anomalies over the equatorial Atlantic and Pacific are opposite-signed, accompanied by anomalous wave sources over the subtropical Southern Hemisphere. The planetary-scale atmospheric response has significant impacts on sea ice concentration anomalies in the Ross Sea, near the Antarctic Peninsula, and east of the Weddell Sea.

To study the effects of graphene oxide (GO), fly ash, and steel fiber on the mechanical properties and durability of concrete, the mechanical properties, frost resistance, and internal pore structure of modified concrete are investigated by compression tests, freeze–thaw cycle tests, and industrial computed tomography (CT) tests. The test results show that the compressive strength of concrete with GO is better than that of mixed concrete, concrete mixed with only steel fiber, and ordinary concrete. Further, it is strongest at all ages when the GO content is 0.03%; the compressive strength of mixed concrete with 30% of fly ash is generally better than that with 15% and 45% of fly ash. In general, the frost resistance of concrete with only GO is better than that of ordinary concrete. With the increase in fly ash content, the internal porosity of concrete decreases, and its compressive strength increases accordingly; as GO increases, the porosity decreases and then increases, with the lowest porosity and the highest compressive strength of concrete at 0.03% of GO. With an increase in porosity, the mass loss and relative dynamic elastic modulus of concrete increase after 100 freeze–thaw cycles, which indicates that porosity directly affects the frost resistance of concrete.

Spatially and temporally explicit information on the biomass in terrestrial ecosystems is essential to better understand the carbon cycle and achieve vegetation resource conservation. As a climate-sensitive critical ecological function area, accurate monitoring of the spatiotemporal variation in the grassland aboveground biomass (AGB) is important in the Three-River Headwater Region (TRHR) of China. In this study, based on field observation, remote sensing, meteorological and topographical data, we estimated the grassland AGB in the TRHR and analyzed its spatiotemporal change and response to climatic factors. Four machine learning (ML) models (random forest (RF), cubist, artificial neural network and support vector machine models) were constructed and compared for AGB simulation purposes. The AGB results estimated with the four ML models were then applied in integrated analysis via Bayesian model averaging (BMA) to obtain more accurate and stable estimates. Our results demonstrated that the RF model performed better among the four ML models (testing dataset: correlation coefficient ( r ) = 0.84; root mean squared error = 76.99 g m ^−2 ), and BMA improved grassland AGB prediction based on the multimodel results. The spatial distribution of the grassland AGB in the TRHR was heterogeneous, with higher values in the southeast and lower values in the northwest. The interannual variation in the grassland AGB in most areas of the TRHR exhibited nonsignificant increasing trends from 2000 to 2018, and the sensitivity of the AGB to the annual precipitation was obviously modulated by regional water conditions. This study provides a more precise method for grassland AGB estimation, and these findings are expected to enable improved assessments to obtain a greater grassland AGB understanding.

A constant supply of novel ideas and contributions from all economic sectors is required to further the sustainable development of cities. Therefore, there is a growing need for well-educated graduates to enter metropolitan job markets. As urban environments and culture have been shown to affect a graduates’ eventual carrier choice and trajectory, governments often seek to change their local environments to attract graduates who can help efficiently allocate and utilize a city’s often-limited environmental budgets. In this study, the conjoint analysis (CA) method was employed to explore the effects of four environmental attributes (water pollution, air pollution, littering, and green area) on graduate employment preferences in northeast China. Water pollution was shown to have the greatest effect on graduate preferences (43.6%), followed by air pollution (34.1%), littering (20.7%), and green area (1.6%). According to this ranking of importance, cities could improve their environmental attributes to maximize the attraction of Northeast graduates. Moreover, this study applied the Baidu index (a big data sharing platform) to improve the attribute selection process of the CA method. The improvement reduced the cost of the CA method and enhanced its objectivity.

Titanium dioxide (TiO _2 ) coated with different proteins has exhibited exceptional bio-compatibility, leading to various biomedical engineering applications. With the use of green and chemical reduction methods, we fabricated Titanium dioxide nanoparticles that were protein-coated. Bovine serum albumin (BSA), lysozyme proteins, zein, and collagen have been used to coat titanium dioxide-aryl nanoparticles of the form TiO _2 -NPs. However, in both cases, no catalysts or other stabilizing agents were used. These images of TiO _2 -NPs fabricated using the green method show high crystallinity. It is a malignant colorectal tumour with dysfunctional cellular processes that cause colorectal cancer cells. It is hoped that studies employing SW1417 cells would give mechanistic ideas on the specifics of the amplification in cancers. This was done by flow cytometry utilizing and laser confocal fluorescence microscopy (LCFM) on the SW1417 colorectal cell line. Of the protein-coated Titanium dioxide nanoparticles fabricated green methods, BSA@TiO _2 -NPs were the most readily absorbed. Of all TiO _2 -NPs, lysozyme@TiO _2 -NPs fabricated by the chemical reduction technique were the most effectively internalized by SW1417 cells out of TiO _2 -NPs types. However, TiO _2 -NPs fabricated by the green methodology were coated with zein and lysozyme and tiny. A hydrophobic covering is also on the two nanoparticles. There is a possibility that the variation in hydrophobicity and charge affected the internalization process. Colorectal diagnostic and therapeutic compounds might be synthesized from those coated nanoparticles that were effectively internalized.

Water shortage is regarded as the most critical constraint limiting the world’s capacity for food security. While previous studies have attributed water scarcity primarily to climate change or some natural factors (e.g. lack of fresh water), few have investigated the impacts of shifts in agricultural systems on water resources. This study quantitatively distinguished the effects of spatiotemporal changes in climatic factors (e.g. temperature and precipitation), planted area, and crop type on China’s irrigation water resources by use of logarithmic mean Divisia index. The results indicated that in the past 25 years (from 1990 to 2015), changes in planted area, crop mix, and climatic factors all led to an increase in irrigation water demand (IWD) in China. Changes in planted area had the greatest effect on IWD (+45.4 × 10 ^9 m ^3 ), followed by the climate change effect (+10.8 × 10 ^9 m ^3 ). In particular, the rapid expansion of maize and other crops in northern China in recent decades has greatly increased irrigation water consumption. It is suggested that in addition to mitigating the adverse effects of climate change, China must address its water scarcity problems by appropriately controlling the scale of some water-intensive crops. These strategies will be essential for adapting agricultural production to future climate change while ensuring food security and water sustainability.

The semi-arid ecosystems dominate the inter-annual variability of the global carbon sink and the driving role of semi-arid ecosystems is becoming increasingly important. However, the impacts of climate change on the dynamics of carbon and water fluxes in global semi-arid ecosystems are still not well understood. We used a data-driven (or machine learning) approach, along with observations from a number of FLUXNET sites and spatially continuous satellite and meteorological data, to generate gridded carbon and water flux estimates for semi-arid regions globally, and then examined the magnitude, spatial patterns, and trends of carbon and water fluxes and their responses to climate change during the period 1982–2015. The average annual gross primary productivity (GPP), net ecosystem productivity (NEP), evapotranspiration (ET), and water use efficiency (WUE) were 628.6 g C m ^−2 yr ^−1 , 9.6 g C m ^−2 yr ^−1 , 463.1 mm yr ^−1 , and 1.60 g C Kg ^−1 H _2 O, respectively. The climate conditions during the period 1982–2015 enhanced gross and net carbon uptake in global semi-arid regions. The spatially-averaged annual GPP, NEP, ET, and WUE in semi-arid regions showed significant increases both globally and regionally (Asia, Africa, and Australia). As with GPP and ET, WUE significantly increased in North America, Asia, Africa, and Australia. Australia was the most sensitive semi-arid region in terms of changes in carbon and water fluxes and their responses to climate. Semi-arid forests, shrublands, and savannas were net carbon sinks; croplands were minor carbon sources; grasslands were nearly carbon neutral. Overall, precipitation was the most important climate factor influencing the carbon and water fluxes; WUE in 40.9% of the semi-arid region was significantly influenced by precipitation. The global climate change is expected to influence global semi-arid ecosystems in many ways and our findings have implications for semi-arid ecosystem management and policy making.

The ductile fracture behavior of 17-4PH martensitic stainless steel at high temperature was investigated based on the experimental data of hot uniaxial tensile test. The elongation and reduction of area indicated that the ductility was mainly enhanced during the deformation at the temperature 1150 °C–1200 °C with high strain rate more than 0.1 s ^−1 . The hot flow stress curves were obtained from the tensile experiments, and the true strain of necking initiation was determined by analyzing the contours of fractured specimens. Then, the true stress-true strain data of the deformations before necking were adopted to establish the tensile flow stress model. In order to express the combined influences of the strain, strain rate and temperature on flow stress, a modified Johnson-Cook model was proposed to describe the hot constitutive behavior of the presented steel. It indicates that reasonable agreements between the model-predicted results and the experimental data were achieved.

The hot deformation behavior of 05Cr17Ni4Cu4Nb stainless steel at the temperatures from 950 °C to 1250 °C and strain rates from 0.01 s ^−1 to 5 s ^−1 was investigated on the basis of test data obtained by Gleeble1500D thermo-simulation machine. A two-stage flow stress constitutive model incorporating the effects of the strain rate and temperature on the deformation behavior is proposed. The stress-strain relations of 05Cr17Ni4Cu4Nb steel predicted by the proposed model agree well with the experimental results. Moreover, the hot processing maps are also investigated. Combined with the microstructure evolution analysis, the appropriate hot forming processing parameters of 05Cr17Ni4Cu4Nb steel is proposed in the temperature range of 1000–1100 °C and strain rate range of 0.01–0.02 s ^−1 .

The effect of Sr and cooling rate on the microstructure of Al-2.5%Mn alloy was studied by OM, SEM and XRD. The results showed that Sr not only refined the primary phase, but also refined eutectic microstructures. However, there was obvious delamination in the alloy. When the content of Sr was 0.2%–0.65%, the primary phase in the upper part of alloy changed from coarse needle and lath-shaped to fine block and needle-like. With the Sr content increased, the needle-like structure in the alloy tended to be more and longer, but the size of α -Al tended to be finer. At the bottom, there were many large massive phases, which were much more refined than the primary phase without Sr With the cooling rate increased, the primary phase was refined greatly and almost all of them transformed into eutectic microstructure. Besides, the delamination of microstructure disappeared.

China’s terrestrial ecosystems play an important role in the global carbon cycle. Regional contributions to the interannual variation (IAV) of China’s terrestrial carbon sink and the attributions to climate variations are not well understood. Here we have investigated how terrestrial ecosystems in the four climate zones with various climate variabilities contribute to the IAV in China’s terrestrial net ecosystem productivity (NEP) using modeled carbon fluxes data from six ecosystems models. Model results show that the monsoonal region of China dominates national NEP IAV with a contribution of 86% (69%–96%) on average. Yearly national NEP changes are mostly driven by gross primary productivity IAV and half of the annual variation results from NEP changes in summer. Regional contributions to NEP IAV in China are consistent with their contributions to the magnitude of national NEP. Rainfall variability dominates the NEP annual variability in China. Precipitation in the temperate monsoon climate zone makes the largest contribution (23%) to the IAV of NEP in China because of both the high sensitivity of terrestrial ecosystem carbon uptake to rainfall and the large fluctuation in the precipitation caused by the East Asian summer monsoon anomalies. Our results suggest that NEP IAV can be mainly attributed to ecosystems with larger productivity and response to precipitation, and highlight the importance of monsoon climate systems with high seasonal and interannual variability in driving internannual variation in the land carbon sink.

AlCoCrFeNiTi is one kind of high entropy alloys with potential applications in aerospace, electronics and machinery manufacturing, etc. Its microstructure, thermodynamic and mechanical properties vary with Al and Ti contents. The disordered structures of Al _x CoCrFeNiTi _1− _x ( x = 0–1.0) alloys were generated and screened with the special quasi-random method. First-principles calculations with the Perdew–Burke–Ernzerhof functional and projector-augmented wave potential were carried out to further identify the structures and assess their thermodynamic and mechanical properties. The measured lattice constants and observed phase transition from bcc to fcc with Ti addition and Al reduction were reproduced in the calculations. The predicted transition point is at the Al content of about 8 at%. The heat capacity of the bcc and fcc structures exhibit similar temperature dependence, matching well with the empirical Dulong-Petit Model and the quantum Debye Model. The elastic constants and elastic moduli vary with the phase structures and compositions. The studied Al _x CoCrFeNiTi _1− _x alloys are predicted to possess good comprehensive mechanical performances, especially for x = 0.8 and 0.6 for the bcc structures and x = 0.5 for the fcc structures. The addition/reduction of Al atoms from the systems alters the electron localization/delocalization that has considerable influence on the interatomic interaction strength in the alloy systems.

The grassland of the Tibetan Plateau forms a globally significant biome, which represents 6% of the world’s grasslands and 44% of China’s grasslands. However, large uncertainties remain concerning the vegetation carbon storage and turnover time in this biome. In this study, we quantified the pool size of both the aboveground and belowground biomass and turnover time of belowground biomass across the Tibetan Plateau by combining systematic measurements taken from a substantial number of surveys (i.e. 1689 sites for aboveground biomass, 174 sites for belowground biomass) with a machine learning technique (i.e. random forest, RF). Our study demonstrated that the RF model is effective tool for upscaling local biomass observations to the regional scale, and for producing continuous biomass estimates of the Tibetan Plateau. On average, the models estimated 46.57 Tg (1 Tg = 10 ^12 g) C of aboveground biomass and 363.71 Tg C of belowground biomass in the Tibetan grasslands covering an area of 1.32 × 10 ^6 km ^2 . The turnover time of belowground biomass demonstrated large spatial heterogeneity, with a median turnover time of 4.25 years. Our results also demonstrated large differences in the biomass simulations among the major ecosystem models used for the Tibetan Plateau, largely because of inadequate model parameterization and validation. This study provides a spatially continuous measure of vegetation carbon storage and turnover time, and provides useful information for advancing ecosystem models and improving their performance.