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Forest–grassland ecotone (FGE) has essential ecological and economic value. Unfortunately, it is impacted greatly by environmental changes and anthropogenic disturbance, and is considered one of the most severely threatened biomes in China. To protect Chinese FGE, identifying its exact boundary and exploring its landscape structure dynamic are badly needed, especially on nationwide scale at one‐year temporal resolution. Here, we mapped the annual FGE distribution of China from 1990 to 2020, investigated its changing trends of area, location and landscape patterns, and revealed the underlying driving factors. Our results showed that FGE area over the 31 years totaled 1 011 870 km2, covering about 10.54% of China's land. The FGE area first increased from 1990 and peaked in 1999, and then kept decreasing until 2020. The FGE gravity center has moved accumulatively 590.15 km over the 31 years, with the net moving distance of 228.76 km southwestward. From 1990 to 2020, forest area increased continuously while grassland and cropland area decreased, but these three landscape types had been dominating the FGE. The increase in forest area was largely converted from grassland. The decline in grassland mainly resulted from its conversion into cropland and forest. Meanwhile, the conversion of cropland to grassland supplemented grassland loss to a certain extent. At landscape level, the total area with decreased fragmentation is larger than that with increased fragmentation. Returning Farmland to Grassland Project and land reclamation were primary drivers for changes of fragmentation in the northern and middle part of the FGE, while temperature and precipitation were primary drivers in southern part. Our results will improve the understanding into the dynamic trends of distribution and pattern of FGE at nationwide scale, and thus help to optimize the designing of ecological projects and protective schemes for FGE as a unique and integral biome. [ABSTRACT FROM AUTHOR]

Abstract: It is well recognized that harsh outer space environment, consisting of microgravity and radiation, poses significant health risks for human cells. To investigate potential effects of the space environment exposure on cancer cells we examined the biological changes in Caski cells carried by the “Shen Zhou IV” spaceship. After exposure for 7 days in spaceflight, 1440 survival subclonal cell lines were established and 4 cell lines were screened. 44F10 and 17E3 were selected because of their increased cell proliferation and tumorigenesis, while 48A9 and 31F2 had slower cytological events. Experiments with cell proliferation assay, flow cytometry, soft agar assay, tumorigenesis assay and DNA microarray analysis have shown that selected cell lines presented multiple biological changes in cell morphology, cell growth, tumorigenicity and gene expression. These results suggest that space environment exposure can make significant biological impact on cancer cells and provide an entry point to find the immunological target of tumorigenesis. [Copyright &y& Elsevier]

[Display omitted] • CQDs were synthesized via coal tar pitch with ozone oxidation method. • The method provides advantages of low-cost, convenience, and environmentally attractive. • CQDs showed a highly sensitivity and selectivity in detection of Fe3+ ions. • CQDs can be used in fluorescence imaging of cells. Carbon quantum dots (CQDs) emerging as newcomers of carbon nanoparticles exhibit fascinating electro-optical properties, and thereby have been widely used in many fields. Herein, we present a new facile, economical and environmentally attractive strategy for the preparation of CQDs via one-step ozone (O 3) treatment of coal tar pitch (CTP). CQDs prepared by this approach exhibit a narrow size distribution between 3–7 nm, and CQDs with a diameter of 4.8 nm accounts for approximately 42.8 %. CQDs were investigated as fluorescent probes for the detection of metal ions, and demonstrated highly sensitive and selective detection of Fe3+ ions. A calibration curve displayed a linear response over the range of 0–9 μM and a detection limit of 0.02 μM (1.12 ppb). Moreover, the photoluminescence performance of the CQDs/Fe3+ complex could be recovered with the addition of EDTA, indicating a great potential for applications of this unique fluorescent CQDs in the detection of Fe3+. Finally, the experiments of CQDs in cell imaging confirmed that the CQDs can be used as potential fluorescent probes in biological imaging, cell labeling with strong luminescence and low toxicity. [ABSTRACT FROM AUTHOR]

Simple Summary: Estimation of population abundance or density is necessary for managing deer populations. However, there is no estimation of Siberian roe deer (Capreolus pygargus) in the Lesser Xing'an Mountains, northeast China where the density of roe deer is much lower than that of European or North American populations. We used fecal-DNA capture-mark-recapture to estimate the abundance and density in Liangshui National Nature Reserve. We collected 422 fecal pellet groups during two sampling periods in 2016, identified them to be 77 individuals by the DNA microsatellite technique and estimated the abundance of roe deer to be 87 deer (80–112, 95% CI) using the Program CAPTURE. Density was estimated to be 2.9 deer/km2 (2.7–3.7, 95% CI). Our study estimated the roe deer population abundance by a feces-based capture-mark-recapture approach in northeast China, successfully demonstrating the applicability of this feces sampling method in monitoring deer populations in this area. It also contributes to the development of low-density deer population ecology and management. It is necessary to estimate the population abundance of deer for managing their populations. However, most estimates are from high-density populations inhabiting the forests of North America or Europe; there is currently a lack of necessary knowledge regarding low-density deer populations in different forest habitats. In this article, we used fecal DNA based on the capture-mark-recapture method to estimate the population abundance of Siberian roe deer (Capreolus pygargus) in Liangshui National Nature Reserve in the Lesser Xing'an Mountains, northeast China, where the deer population was found to be of a low density by limited studies. We used a robust survey design to collect 422 fecal pellet groups in 2016 and extracted DNA from those samples, generating 265 different genotypes; we thus identified 77 deer individuals based on six microsatellite markers (Roe1, Roe8, Roe9, BM757, MB25 and OarFCB304). With capture and recapture records of these 77 individuals, the abundance of roe deer was estimated to be 87 deer (80–112, 95% CI) using the Program CAPTURE. Using an effective sampling area which resulted from the mean maximum recapture distance (MMRD), we converted the population abundance to a density of 2.9 deer/km2 (2.7–3.7, 95% CI). Our study estimated the roe deer population abundance by a feces-based capture-mark-recapture approach in northeast China, successfully demonstrating the applicability of non-invasive genetic sampling in monitoring populations of deer in this area, which contributes to the development of low-density deer population ecology and management. [ABSTRACT FROM AUTHOR]

Domain walls are of increasing interest in ferroelectrics because of their unique properties and potential applications in future nanoelectronics. However, the thickness of ferroelastic domain walls remains elusive due to the challenges in experimental characterization. Here, we determine the atomic structure of ferroelastic domain walls and precisely measure the polarization and domain wall thickness at picometer scale using annular bright field imaging from an aberration-corrected scanning transmission electron microscope. We find that the domain wall thickness in PbZr 0.2 Ti 0.8 O 3 and PbTiO 3 thin films is typically about one unit cell, across which the oxygen octahedron distortion behavior is in excellent agreement with previous first-principles calculations. Remarkably, wider domain walls about two unit cells in thickness are also observed for those domains walls are coupled with dislocations and underwent a compressive strain. These results suggest that the thickness of ferroelastic domain walls highly depends on their atomic environments. This study can help us to understand the past debatable experimental results and provide further insights into control of domain wall thickness via strain engineering for their possible applications in nanoelectronics. Image, graphical abstract [ABSTRACT FROM AUTHOR]

[Display omitted] • Well-defined cyclic carbamoyl-Mn(I) complexes are prepared with improved stability. • Carbamoyl-Mn(I) accelerates alkenes epoxidation via Mn(III)=O and Mn(II)-O species. • CO 2 cycloaddition of epoxides was promoted by acidic N–H proton in carbamoyl unit. There is no precedent for the usage of transition metal carbamoyl complexes (typical hydrogenase models) as pre-catalysts for oxidation or CO 2 utilization purposes. In this work, we describe that carbamoyl-Mn(I) complexes are capable of selectively catalyzing both epoxidation of olefins and epoxides with carbon dioxide to form cyclic carbonates. The dual-role catalytic system was well adapted to a wide range of aromatic olefins, and the desired cyclic carbonates were obtained in moderate to excellent yields. Mechanistic investigations indicated that active Mn(II)-oxo and Mn(III)-oxo species were involved in the oxidation process. [ABSTRACT FROM AUTHOR]

[Display omitted] • Achieving a direct olefin epoxidation with water as the sole oxygen source. • α-MnO 2 exposed with (3 1 0) facet exhibited superior activity and stability. • Oxygen vacancies played a key role in oxygen atom transfer process. • MnOOH reactive intermediate was observed in an organic electrolyte. Electrocatalytic epoxidation, utilizing sustainable water and electricity as clean oxygen source and chemical oxidant surrogates respectively, represents an attractive approach toward industrial applications. However, the low yield and selectivity of epoxides are still a formidable challenge in satisfying industrial demand. Herein, we demonstrated a crystal facet engineering strategy over α-MnO 2 catalysts for enhancing electrocatalytic epoxidation. Compared with α-MnO 2 -110 and α-MnO 2 -100, the α-MnO 2 exposed with (3 1 0) facet exhibited excellent activity. Furthermore, a 21-fold yield increase was obtained compared with the reported superior Mn-based electrocatalyst. These results revealed that crystal facet engineering could induce the formation of more oxygen vacancies and weaken the interaction of Mn-O band to regulate oxygen atom transfer capacity. In addition, the reactive intermediate (MnOOH) was observed in an organic electrolyte, which was confirmed by in situ Raman spectra and isotope labeling experiment. [ABSTRACT FROM AUTHOR]

An efficient palladium-manganese system for the Markovnikov selective alkoxycarbonylation reaction of aromatic and aliphatic alkenes was developed. [Display omitted] • A general and efficient palladium-manganese system for the Markovnikov selective alkoxycarbonylation reaction of alkenes. • By using the carbazole-derived phosphine ligand containing bipyridine moiety, various aromatic and aliphatic olefins were transformed into the corresponding esters in good yields with moderate to high branched selectivity. • Preliminary mechanistic studies reveal the respective contribution of palladium and manganese centers to achieve highly branch-selective alkoxycarbonylations. Carbazole derived phosphine ligands containing pyridine moiety were designed and prepared. It allows the challenging Pd-catalyzed Markovnikov-selective alkoxycarbonylation of aliphatic alkenes to give the branched ester products (28 examples; 51–97% branch selectivity). Preliminary mechanistic studies support that the bridging bromide between Pd and Mn centers is crucial for the enhancement of regioselectivity. [ABSTRACT FROM AUTHOR]

Wetlands, as the most essential ecosystem, are degraded throughout the world. Wetlands in Zhenlai county, with the Momoge National Nature Reserve, which was included on the Ramsar list, have degraded by nearly 30%. Wetland degradation is a long-term continuous process with annual or interannual changes in water area, water level, or vegetation presence and growth. Therefore, it requires sufficiently frequent and high-spatial-resolution data to represent its dynamics. This study mapped yearly land-use maps with 30-m resolution from 1985 to 2018 using Landsat data in Google Earth Engine (GEE) to explore the wetland degradation process and mapped 12-day interval land-use maps with 15-m resolution using the Sentinel-1B and Sentinel-2 data in GEE and other assistant platforms to study the characteristics of wetland dynamics in 2018. Four sets of maps were generated using Sentinel-1B (S1), Sentinel-2 (S2), the combination of Sentinel-1B and Sentinel-2 (S12), and S12 with multitemporal remote sensing (S12'). All of the classifications were performed in the Random Forest Classification (RFC) method using remote sensing indicators. The results indicate that S12' was the most accurate. Then, the impact of the historic land-use degradation process on current wetland change dynamics was discussed. Stable, degradation, and restoration periods were identified according to the annual changes in wetlands. The degraded, stable, restored, and vulnerable zones were assessed based on the transformation characteristics among wetlands and other land-use types. The impact of historical land-use trajectories on wetland change characteristics nowadays is diverse in land-use types and distributions, and the ecological environment quality is the comprehensive result of the effect of historical land-use trajectories and the amount of rainfall and receding water from paddy fields. This study offers a new method to map high-spatiotemporal-resolution land-use (S12') and addresses the relationship between historic wetland change characteristics and its status quo. The findings are also applicable to wetland research in other regions. This study could provide more detailed scientific guidance for wetland managers by quickly detecting wetland changes at a finer spatiotemporal resolution. [ABSTRACT FROM AUTHOR]

A novel approach involving molybdenum disulfide (MoS 2) promoted in-situ generation of cobalt catalyst for alkoxycarbonylation reaction was presented. Cobalt(II) salts were transformed to highly active cobalt carbonyl species without using external reducing agents or applying harsh reaction conditions. Mechanism studies revealed that the defect-rich MoS 2 played the key role to abstract electron from CO and to reduce Co2+. [Display omitted] • S-defect MoS 2 promoted cobalt(II) reduction to cobalt(0) with CO as reductant under mild conditions. • Inexpensive and stable cobalt acetate as catalyst precursor instead of Co 2 (CO) 8. • MoS 2 with sulfur defects serves dual roles to abstract electron from CO and to reduce Co2+. • This work provides strategies for in-situ generation of low-valence metallic species. Herein, we presented a novel approach involving molybdenum disulfide (MoS 2) promoted in-situ generation of active cobalt catalyst for alkoxycarbonylation reaction, an industrial process for ester production. In this scenario, inexpensive cobalt(II) salts were transformed to highly active cobalt carbonyl species without using external reducing reagents or applying harsh reaction conditions. In-situ formed cobalt catalyst enabled high activity comparable to that using Co 2 (CO) 8 as catalyst. The generation of [Co(CO) 4 ]- anion under mild conditions was confirmed by both in-situ Fourier transformed infrared spectroscopy (FT-IR) and electrospray ionization mass spectrometry (ESI-MS). The detailed mechanism of this transformation revealed by X-ray photoelectron spectroscopy (XPS) and electrochemical analysis involved that carbon monoxide (CO) served dual roles as reductant and carbonyl ligand while the electron transfer to Co2+ cation took place over the MoS 2 surface with sulfur defects. [ABSTRACT FROM AUTHOR]

[Display omitted] • The first efficient ligand free iron-catalyzed hydroaminocarbonylation of alkynes to produce succinimides with NH 4 HCO 3 as the ammonia source. • With NH 4 HCO 3 as easy-to-handle ammonia source, a variety of internal and terminal alkynes were well tolerated in this catalytic system. • Preliminary mechanistic studies reveal the activation model involving interactions of NH 4 HCO 3 with both iron catalyst and alkyne substrates. Succinimide derivatives are valuable compounds in synthesis of natural products and pharmaceuticals. A catalytic hydroaminocarbonylation reaction was developed for the synthesis of succinimides from alkynes, CO and NH 4 HCO 3. The novel transformation proceeds in the presence of Fe 3 (CO) 12 without the need for expensive ligands or additives. Various substituted alkynes are selectively transformed into corresponding succinimides in good yields. Preliminary mechanistic studies suggest that NH 4 HCO 3 plays an important role in the formation and stabilization of iron catalyst. [ABSTRACT FROM AUTHOR]

Reductive Strecker reaction of formamides to afford amino-acetonitriles was achieved via FeI 2 -catalysis. [Display omitted] • A new method to access amino acetonitriles using FeI 2 catalyst. • Better yields obtained than the use of Ir- or Rh-catalysts. • One pot synthesis of 13C-labelled amino acetonitriles from 13C-CO 2. • Successful application toward modular synthesis of acids, amines, heterocycles, etc. Strecker reaction is widely applied for the synthesis of amino acids from aldehydes, amines and cyanides. Herein, we report the FeI 2 -catalyzed reductive Strecker type reaction of formamides instead of aldehydes to produce amino acetonitriles. The challenging capture of carbinolamine intermediates by CN− was achieved via Fe catalysis. This approach afforded better yields than the use of Ir- or Rh-catalysts. The application ability of this methodology is demonstrated by 1) one-pot construction of (13C labeled) complex molecules from CO 2 via amino acetonitrile intermediates and 2) convenient production of homologated carboxylic acids from aldehydes. [ABSTRACT FROM AUTHOR]

Contact interface properties are important in determining the performances of devices that are based on atomically thin two-dimensional (2D) materials, especially for those with short channels. Understanding the contact interface is therefore important to design better devices. Herein, we use scanning transmission electron microscopy, electron energy loss spectroscopy, and first-principles calculations to reveal the electronic structures within the metallic (1T′)-semiconducting (2H) MoTe2 coplanar phase boundary across a wide spectral range and correlate its properties to atomic structures. We find that the 2H-MoTe2 excitonic peaks cross the phase boundary into the 1T′ phase within a range of approximately 150 nm. The 1T′-MoTe2 crystal field can penetrate the boundary and extend into the 2H phase by approximately two unit-cells. The plasmonic oscillations exhibit strong angle dependence, that is a red-shift of π+σ (approximately 0.3–1.2 eV) occurs within 4 nm at 1T′/2H-MoTe2 boundaries with large tilt angles, but there is no shift at zero-tilted boundaries. These atomic-scale measurements reveal the structure–property relationships of the 1T′/2H-MoTe2 boundary, providing useful information for phase boundary engineering and device development based on 2D materials. [ABSTRACT FROM AUTHOR]

• P/N-H ligand facilitates Ru to exhibit efficient hydrogenation under CO. • The NH effect of ligands promote the hydrogenation process. • Co/Ru- L1 system smoothly achieves alcohol production under hydroformylation conditions. Efficient hydrogenation of aldehydes is highly desirable in hydroformylation process to obtain alcohol products. This work developed carbazole-derived phosphine ligands for efficient Ru-catalyzed hydrogenation of aldehydes in the presence of carbon monoxide. Up to 99 % yields of alcohols were obtained in the presence of high-pressure CO at 130 ℃. The results of different ligands revealed the crucial role of N H moiety on carbazole in promoting the catalytic hydrogenation. It was applied to the Co/Ru-catalyzed hydroformylation process, resulting in the production of long-chain alcohols with excellent yields. [Display omitted] [ABSTRACT FROM AUTHOR]

Defects exist ubiquitously in crystal materials, and usually exhibit a very different nature from the bulk matrix. Hence, their presence can have significant impacts on the properties of devices. Although it is well accepted that the properties of defects are determined by their unique atomic environments, the precise knowledge of such relationships is far from clear for most oxides because of the complexity of defects and difficulties in characterization. Here, we fabricate a 36.8° SrRuO3 grain boundary of which the transport measurements show a spin-valve magnetoresistance. We identify its atomic arrangement, including oxygen, using scanning transmission electron microscopy and spectroscopy. Based on the as-obtained atomic structure, the density functional theory calculations suggest that the spin-valve magnetoresistance occurs because of dramatically reduced magnetic moments at the boundary. The ability to manipulate magnetic properties at the nanometer scale via defect control allows new strategies to design magnetic/electronic devices with low-dimensional magnetic order. [ABSTRACT FROM AUTHOR]

Catalytic carbonylations of alkynes represent straightforward and atom-economic synthesis of α,β-unsaturated carbonyl compounds. One of the issues associated with the currently known catalytic systems is insufficient efficiency. In this context, Pd/ligand-catalyzed regioselective and efficient alkoxycarbonylation of terminal alkynes is desirable for the synthesis of α,β-unsaturated esters. Herein, we present the use of a newly designed bifunctional ligand for efficient Pd-catalyzed alkoxycarbonylation of alkynes. Both aliphatic and aromatic alkynes were smoothly transformed to the branched desired products with high selectivity (28 examples, 45–96% yields, 95.0–99.9% selectivity). [ABSTRACT FROM AUTHOR]

The influence of Cr on the interfacial bonding and erosion-corrosion resistance of ZrO 2 -Al 2 O 3 particles reinforced high chromium white cast irons based (ZTA P /Fe) composites were systematically investigated. The Cr coatings on the surface of ZTA particle (ZTA P) ceramics were fabricated by multi-arc ion plating. The results indicated that a uniform and continuous Cr coating was tightly adhered with ZTA ceramic substrate. The thickness and grain size of the Cr coating could be effectively controlled by regulating the deposition parameters. The grain size of Cr coating increased with deposition time. The ZTA P /Fe composites assisted without (N1) and with (N2) Cr coating were prepared via infiltration casting. The addition of Cr coating obtained a smooth and tight interface, attributed to the improvement of the wettability between ZTA ceramic and high chromium white cast irons matrix (Cr15). Moreover, the erosion-corrosion resistance property of the Cr coated ZTA P /Fe composites (N2) improved up to 44% compared with bare-ZTA P /Fe composites (N1) due to their interfacial enhancement action. Meanwhile, the interfacial layer of the N2 composites had a low roughness after erosion-corrosion. • The continuous Cr coating could be obtained by multi-arc ion plating. • A Cr15-based composites reinforced with Cr-coated ZTA P ceramic was fabricated. • Cr coating could improve the interfacial properties of ZTA P /Fe composites. • The effect of Cr on erosion-corrosion resistance of ZTA P /Fe composites were investigated. [ABSTRACT FROM AUTHOR]

NH3 is a valuable chemical with a wide range of applications, but the conventional Haber–Bosch process for industrial‐scale NH3 production is highly energy‐intensive with serious greenhouse gas emission. Electrochemical reduction offers an environmentally benign and sustainable route to convert N2 to NH3 at ambient conditions, but its efficiency depends greatly on identifying earth‐abundant catalysts with high activity for the N2 reduction reaction. Here, it is reported that MnO particles act as a highly active catalyst for electrocatalytic hydrogenation of N2 to NH3 with excellent selectivity. In 0.1 m Na2SO4, this catalyst achieves a high Faradaic efficiency up to 8.02% and a NH3 yield of 1.11 × 10−10 mol s−1 cm−2 at −0.39 V versus reversible hydrogen electrode, with great electrochemical and structural stability. On the basis of density functional theory calculations, MnO (200) surface has a smaller adsorption energy toward N than that of H with the *N2 → *N2H transformation being the potential‐determining step in the nitrogen reduction reaction. A manganese oxide particles film on Ti mesh (MnO/TM) acts as a robust non‐noble‐metal electrocatalyst for efficient N2 reduction electrocatalysis at ambient conditions. In 0.1 m Na2SO4, the MnO/TM attains a high Faradaic efficiency up to 8.02% and a NH3 yield of 1.11 × 10−10 mol s−1 cm−2 at −0.39 V versus reversible hydrogen electrode, with high electrochemical stability. [ABSTRACT FROM AUTHOR]