Both natural and human-induced disturbances affect the normal functioning and services of mangrove ecosystems.To address the consequences of intense human and climatic disturbances on sedimentation and carbon burial,s...Both natural and human-induced disturbances affect the normal functioning and services of mangrove ecosystems.To address the consequences of intense human and climatic disturbances on sedimentation and carbon burial,sediment cores from the last remaining mangrove Kandelia obovata forest and an adjacent mudflat in the densely populated and typhoon-prone Zhujiang(Pearl)River estuary of China,were analyzed using methods including^(210)Pb dating andδ^(13)C analysis.Results indicate that after damming in the 1950s,during 1960-1980,the natural establishment of K.obovata forests initiated the insitu sedimentation.As these forests matured during 1980-1990,they significantly boosted siltation in the region on mudflat.During 1990-2015,the invasion of Spartina alterniflora and land reclamation for aquaculture caused infiltration of coarse sediments and the impacts of typhoons were recorded within the K.obovata forest,while no clear typhoon record was observed on the mudflat.Since 2015,reforestation efforts with S.apetala that began in 1999 have reversed the effects of earlier deforestation.Over time,mangroves established a rapid autochthonous carbon burial that grew as the forests age,potentially surpassing the influx of allochthonous carbon due to deforestation.The reforestation also immediately improved carbon burial on the mudflat,which stabilized after a decade due to the rapid growth and high biomass of S.apetala.Overall,the K.obovata forest demonstrated a stronger sedimentation and carbon burial capabilities than the mudflat,with a surplus of 35.2 Mg C/hm^(2)in soil organic carbon stock and 1.0 Mg C/(hm^(2)·a)in burial rate.Organic matter dissolved in soil was mainly humus-like components,and mangrove inputs likely increased the degree of humification.This study offered direct evidence regarding the impact of multiple disturbances on local and regional sedimentation and carbon burial,and future management strategies.展开更多
Continuous cropping has become a common form of agricultural production at present, but with the increase of continuous cropping years, continuous cropping obstacles such as soil-borne diseases and plant growth potent...Continuous cropping has become a common form of agricultural production at present, but with the increase of continuous cropping years, continuous cropping obstacles such as soil-borne diseases and plant growth potential decline are becoming more and more common. At present, the causes of continuous cropping obstacles and continuous cropping restoration have become a hot issue in agricultural research. This paper summarized the effects of continuous cropping obstacles on soil microbial community structure and main technical methods to repair continuous cropping obstacles, such as agricultural measure management, microbial balance adjustment and soil improvement, aiming to provide theoretical reference for protecting the sustainable utilization of soil ecosystem and ensuring the stability of crop production.展开更多
The challenge of establishing top-down constraints for regional emissions of fossil fuel CO_(2)(FFCO_(2))arises from the difficulty in distinguishing between atmospheric CO_(2)concentrations released from fossil fuels...The challenge of establishing top-down constraints for regional emissions of fossil fuel CO_(2)(FFCO_(2))arises from the difficulty in distinguishing between atmospheric CO_(2)concentrations released from fossil fuels and background variability,particularly owing to the influence of terrestrial biospheric fluxes.This necessitates the development of a regional inversion methodology based on atmospheric CO_(2)observations to verify bottom-up estimations independently.This study presents a promising approach for estimating China's FFCO_(2)emissions by incorporating the model residual errors(MREs)of the column-averaged dry-air mole fractions of CO_(2)(XCO_(2))from FFCO_(2)emissions(MREff)retained in the analysis of natural flux optimization.China's FFCO_(2)emissions during the COVID-19 lockdown in 2020 are estimated using the GEOS-Chem adjoint model.The relationship between the MREff and FFCO_(2)is determined using the model based on a regional FFCO_(2)anomaly suggested by posterior NOx emissions from air-quality data assimilation.The MREff is typically one-tenth in magnitude,but some positively skewed outliers exceed 1 ppm because the prior emissions lack lockdown impacts,thereby exerting considerable observation forcing given the satellite retrieval uncertainties.We initialize the FFCO_(2)with posterior NOx emissions and optimize the colinear emission ratio.Synthetic data experiments demonstrate that this approach reduces the FFCO_(2)bias to less than 10%.The real-data experiments estimate 19%lower FFCO_(2)with GOSAT XCO_(2)and 26%lower with OCO-2 XCO_(2)than the bottom-up estimations.This study proves the feasibility of our regional FFCO_(2)inversion,highlighting the importance of addressing the outlier behaviors observed in satellite XCO_(2)retrievals.展开更多
Isotropic pyrolytic carbon(IPC)is renowned for its robust mechanical,biological,and tribological prop-erties.However,the current mechanisms for modulating IPC microstructure are insufficient to achieve higher performa...Isotropic pyrolytic carbon(IPC)is renowned for its robust mechanical,biological,and tribological prop-erties.However,the current mechanisms for modulating IPC microstructure are insufficient to achieve higher performance.Herein,this study provides nanoscale insights into the formation and property reg-ulation of the core-shell structure of the IPC,integrating simulation and experimental approaches.Large-scale reactive molecular dynamics simulations elucidate the microstructural evolution and assembly pro-cesses from precursors to nanoparticles and intertwined graphene networks.Simulation process charac-terization enable versatile adjustment of IPC microstructural features and one-step deposition of hybrid structures with disordered cores and ordered shell layers.Compared to Pyrolytic carbon(PyC)with lam-inated graphene arrangement,the prepared hybrid structure enables rapid assembly of large-size stan-dalone carbon components.Moreover,the hybrid architecture effectively improves the core-shell phase connection and significantly increases the interfacial shear stress within the intertwined graphene shell layers.Consequently,it greatly improves load transfer efficiency and enhances crack-bridging toughening effect.The endeavor to establish precise microstructure formation and property regulation in IPC materi-als promises to steer high-performance carbon materials toward distinct developmental trajectories.展开更多
Carbon nanotubes(CNTs)hold immense promise for a wide array of applications due to their exceptional physical and chemical properties.Understanding and controlling their structural characteristics,particu-larly the di...Carbon nanotubes(CNTs)hold immense promise for a wide array of applications due to their exceptional physical and chemical properties.Understanding and controlling their structural characteristics,particu-larly the diameter and number of walls,is crucial for harnessing their full potential.We investigated the relationship between these parameters for both commercially available and lab-scale CNTs,spanning a wide range of outer diameters(1-13 nm)and numbers of walls(1-13).Our findings revealed a com-monality among the structural diversity,rather than a random distribution,as evidenced by a piecewise linear relationship between the outer diameter and number of walls,with an inflection point occurring at approximately 4 nm in diameter.This observation is unexpected,as the CNTs were synthesized using different approaches and growth conditions;yet,as a group,they exhibit a“structural scaling”.Addi-tionally,we made an intriguing observation:despite increases in outer diameter and number of walls,the inner diameters remained relatively constant(4-5 nm)for thicker CNTs with more than three walls.These results suggest that structural properties can be estimated based on diameter,which not only ad-vances our fundamental understanding of CNT synthesis but also provides practical insights for tailoring CNT properties for various applications.展开更多
Oxygen isotope(δ^(18)O)of paleolake water is a key indicator for reconstructing the formation temperature and diagenetic history of lacustrine carbonate minerals.In this study,we use clumped isotopes(Δ_(47))of lacus...Oxygen isotope(δ^(18)O)of paleolake water is a key indicator for reconstructing the formation temperature and diagenetic history of lacustrine carbonate minerals.In this study,we use clumped isotopes(Δ_(47))of lacustrine shell limestones to determine the surface erosion thickness and δ^(18)O of Early Jurassic lake water in the northern Sichuan Basin.We analyzed nine shell limestone and seventeen shale samples from the Early Jurassic Da'anzhai Member(J_(1)z^(4))in the Yuanba area.Whether the shell's shapes are well or partially preserved,the J_(1)z^(4)shell limestones in the Yuanba area show no significant recrystallization and dull cathodoluminescence.These characteristics suggest that the shell limestones did not undergo significant diagenetic alteration during late burial.The Δ_(47)values of the J_(1)z^(4)shell limestones range from 0.448±0.005‰to 0.463±0.006‰,yielding clumped isotope temperature(T_(Δ47))of 64.4±0.8 to 69.7±1.4℃,which is significantly higher than the Early Jurassic paleotemperature.It suggests that the Δ_(47)of shell limestones was altered by solid-state reordering,meaning the T_(Δ47)does not reflect the initial formation temperatures.By integrating organic matter's maturation model(Easy%R_(o))of coexisting shales with Δ_(47)solid-state reordering model of calcite,we constrained the maximum burial temperature(~170℃)and the initial formation temperature(~28℃)of these shell limestones.Based on reported paleotemperature gradient,we estimated that the surface erosion thickness was about 1500 m.Furthermore,using the determined initial formation temperatures and conventional oxygen isotope thermometer,we determined that the δ^(18)O values of the Early Jurassic lake water in the Sichuan Basin,which ranged from-10.8‰to-8.0‰(SMOW).The reconstructed paleo temperature and δ^(18)O of lake water suggest that the Early Jurassic in the Sichuan Basin was warm and humid,which was favorable for the deposition of organic-rich lacustrine shale.The methods developed in this study,which employ Δ_(47)of shell limestones to reconstruct the maximum burial temperature and paleolake environmental conditions,demonstrate broad applicability to the Sichuan Basin and similar lacustrine basins.展开更多
With the swift advancement of industrial automation,robots have emerged as an essential component in emerging industries and high-end equipment,thereby propelling industrial production towards greater intelligence and...With the swift advancement of industrial automation,robots have emerged as an essential component in emerging industries and high-end equipment,thereby propelling industrial production towards greater intelligence and efficiency.This paper reviews the pivotal technologies for motion planning of robots engaged in contact tasks within industrial automation contexts,encompassing environmental recognition,trajectory generation strategies,and sim-to-real transfer.Environmental recognition technology empowers robots to accurately discern objects and obstacles in their operational environment.Trajectory generation strategies formulate optimal motion paths based on environmental data and task specifications.Sim-to-real transfer is committed to effectively translating strategies from simulated environments to actual production,thereby diminishing the discrepancies between simulation and reality.The article also delves into the application of artificial intelligence in robot motion planning and how embodied intelligence models catalyze the evolution of robotics technology towards enhanced intelligence and automation.The paper concludes with a synthesis of the methodologies addressing this challenge and a perspective on the myriad challenges that warrant attention.展开更多
One of the significant technological challenges in safeguarding electronic devices pertains to the modulation of electromagnetic(EM)wave jamming and the recycling of defensive shields.The synergistic effect of heterod...One of the significant technological challenges in safeguarding electronic devices pertains to the modulation of electromagnetic(EM)wave jamming and the recycling of defensive shields.The synergistic effect of heterodimensional materials can effectively enable the manipulation of EM waves by altering the nanostructure.Here we propose a novel approach for upcycling by-products of silver nanowires that can fabricate shape-tunable aerogels which enable the modulation of its interaction with microwaves by heterodimensional structure of byproducts.By-product heterodimensionality was used to design EM-wave-jamming-dissipation structures and therefore two typical tunable aerogel forms were studied.The first tunable form was aerogel film,which shielded EM interference(EMI shielding effectiveness(EMI SE)>89 dB)and the second tunable form was foam,which performed dual EM functions(SE>30 dB&reflective loss(RL)<-35 dB,effective absorption bandwidth(EAB)>6.7 GHz).We show that secondary recycled aerogels retain nearly all of their EM protection properties,making this type of closed-loop cycle an appealing option.Our findings pave the way for the development of adaptive EM functions with nanoscale regulation in a green and closed-loop cycle,and they shed light on the fundamental understanding of microwave interactions with heterodimensional structures.展开更多
The Hyperspectral Infrared Atmospheric Sounder-II(HIRAS-II)onboard China’s FungYun(FY)-3F meteorological satellite was launched in August 2023.This study presents the first attempt to retrieve the global carbon monox...The Hyperspectral Infrared Atmospheric Sounder-II(HIRAS-II)onboard China’s FungYun(FY)-3F meteorological satellite was launched in August 2023.This study presents the first attempt to retrieve the global carbon monoxide(CO)column from HIRAS-II/FY-3F spectra based on a newly established full-physics algorithm.The CO global columns derived from the HIRAS-II/FY-3F satellite are compared to measurements from the Infrared Atmospheric Sounding Interferometer(IASI)onboard Europe’s MetopB satellite,as both satellites have the same spectral range with a similar overpass time.The correlation coefficient between the IASI/Metop-B and HIRAS-II/FY-3F CO retrievals is about 0.8.The HIRAS-II/FY-3F satellite can capture well the regions with high CO values,e.g.,Africa,North America,and East Asia.The relative difference in the CO global column between HIRAS-II and IASI is 1.2±13.7(1)%,which is within their combined retrieval uncertainty.The CO plumes from the fire emissions in North America between 18 and 23 July 2024 were observed by the HIRAS-II/FY-3F satellite and consistent with the CAMS(Copernicus Atmosphere Monitoring Service)model simulations.Our results show that the HIRAS-II/FY-3F spectra are of good enough quality to provide quantitative observations of global CO column remote sensing observations.展开更多
Weak radiative hyperon decays represent a rich interplay between weak interactions and the internal structure of baryons,offering profound insights into Quantum Chromodynamics and weak interactions.Recent experimental...Weak radiative hyperon decays represent a rich interplay between weak interactions and the internal structure of baryons,offering profound insights into Quantum Chromodynamics and weak interactions.Recent experimental observations,particularly from BESIII,have revealed deviations from theoretical predictions.These deviations could signal new physics or the need for refined theoretical models incorporating intermediate resonance effects.This review discusses recent theoretical advancements and key experimental findings,focusing on recent measurements from BESIII and their implications for strong interactions and baryon structure.展开更多
Hypernuclei,nuclei containing one or more hyperons,serve as unique laboratories for probing the non-perturbative quantum chromodynamics(QCD).Recent progress in hypernuclear physics,driven by advanced experimental tech...Hypernuclei,nuclei containing one or more hyperons,serve as unique laboratories for probing the non-perturbative quantum chromodynamics(QCD).Recent progress in hypernuclear physics,driven by advanced experimental techniques and theoretical innovations,is briefly reviewed with a focus on key findings and unresolved challenges,such as the precise determination of the hypertriton binding energy,investigations of charge symmetry breaking in mirror hypernuclei,and the search for exotic systems,including the neutral nnΛstate.Experimental breakthroughs,including invariant-mass analyses and femtoscopy studies in heavy-ion collisions,as well as high-resolutionγ-spectroscopy,have enabled precise studies of light hypernuclei and offered critical insights into the hyperon–nucleon interaction.Theoretical progress,including ab initio calculations based on chiral effective field theory and lattice QCD,has further enhanced our understanding of hyperon–nucleon and hyperon–hyperon interactions.展开更多
Accurate acid placement constitutes a major concern in matrix stimulation because the acid tends to penetrate the zones of least resistance while leaving the low-permeability regions of the formation untreated.Degrada...Accurate acid placement constitutes a major concern in matrix stimulation because the acid tends to penetrate the zones of least resistance while leaving the low-permeability regions of the formation untreated.Degradable materials(fibers and solid particles)have recently shown a good capability as fluid diversion to overcome the issues related to matrix stimulation.Despite the success achieved in the recent acid stimulation jobs stemming from the use of some products that rely on fiber flocculation as the main diverting mechanism,it was observed that the volume of the base fluid and the loading of the particles are not optimized.The current industry lacks a scientific design guideline because the used methodology is based on experience or empirical studies in a particular area with a particular product.It is important then to understand the fundamentals of how acid diversion works in carbonates with different diverting mechanisms and diverters.Mathematical modeling and computer simulations are effective tools to develop this understanding and are efficiently applied to new product development,new applications of existing products or usage optimization.In this work,we develop a numerical model to study fiber dynamics in fluid flow.We employ a discrete element method in which the fibers are represented by multi-rigid-body systems of interconnected spheres.The discrete fiber model is coupled with a fluid flow solver to account for the inherent simultaneous interactions.The focus of the study is on the tendency for fibers to flocculate and bridge when interacting with suspending fluids and encountering restrictions that can be representative of fractures or wormholes in carbonates.The trends of the dynamic fiber behavior under various operating conditions including fiber loading,flow rate and fluid viscosity obtained from the numerical model show consistency with experimental observations.The present numerical investigation reveals that the bridging capability of the fiber–fluid system can be enhanced by increasing the fiber loading,selecting fibers with higher stiffness,reducing the injection flow rate,reducing the suspending fluid viscosity or increasing the attractive cohesive forces among fibers by using sticky fibers.展开更多
C/C-ZrC composites with continuous ZrC matrix were prepared by precursor infiltration and pyrolysis process using zirconium-containing polymer.Ablation properties of the composites were investigated by oxyacetylene fl...C/C-ZrC composites with continuous ZrC matrix were prepared by precursor infiltration and pyrolysis process using zirconium-containing polymer.Ablation properties of the composites were investigated by oxyacetylene flame with heat flux of 2380 and 4180 kW/m2,respectively.The results showed that C/C-ZrC composites exhibited excellent ablation resistance under the heat flux of 2380 kW/m2for 120 s and a tree-coral-like ZrO2protective layer formed after ablation.However,when the heat flux increased to 4180 kW/m2,the maximum temperature of ablated surface reached 2500 ℃ and a strong degradation of ablation resistance was observed due to the weak bonding between the formed ZrO2layer and the composites.The flexural strength of C/C-ZrC composites was 110.7 ± 7.5 MPa.There were a large number of carbon fiber bundles pull-out,and the composites exhibited a pseudo-plastic fracture behavior.展开更多
To effectively get the thermal expansion coef- ficient （CTE） of three-dimensional （3D） braided C/C composites and study the variations, a VC＋＋ program with graphical user interfaces was obtained, based on the ya...To effectively get the thermal expansion coef- ficient （CTE） of three-dimensional （3D） braided C/C composites and study the variations, a VC＋＋ program with graphical user interfaces was obtained, based on the yam unit model and numerical analysis. With the limited basic properties of carbon fibers and carbon matrix, CTE of 3D braided C/C composites is obtained at 85 ~C. The deviation between the simulated and exl^erimental axial CTE of 3D braided C/C composites is no more than 11%. The effects of different parameters （including the braiding angle of 3D braided preform, the fiber volume fraction and the porosity of 3D braided C/C composites, and the elastic modulus, Poisson＇s ratio and CTEs of carbon fibers and carbon matrix） were analyzed with the program. The results show that the axial CTE of C/C composites decreases with the increase of the braiding angle, the fiber volume fraction, and the porosity of 3D braided C/C composites. The transverse elastic modulus of carbon fibers has the greatest effect on the axial CTE among the studied mechanical parameters, followed by the elastic modulus and Poisson＇s ratio of carbon matrix.展开更多
Hierarchical Co_(3)O_(4)@NiCoLDH nanosheets(NSs)were prepared on carbon cloth through a multistep method,containing Metal-organic frameworks(MOF)-templated thermal annealing and electrodeposition.The triangle-shaped C...Hierarchical Co_(3)O_(4)@NiCoLDH nanosheets(NSs)were prepared on carbon cloth through a multistep method,containing Metal-organic frameworks(MOF)-templated thermal annealing and electrodeposition.The triangle-shaped Co_(3)O_(4 NSs)were firstly obtained by thermal treatment of MOF templates in air.Then,ultrathin NiCoLDH_(NSs)were in-situ electrodeposited on the surface of Co_(3)O_(4NSs),constructing a core-shell structure.Benefiting the unique hierarchical structure,high conductivity of Co_(3)O_(4 NSs)core and large surface area of NiCoLDHNSs shell,the Co_(3)O_(4)@NiCoLDH_(NSs)array served as supercapacitor electrode exhibits excellent electrochemical properties,such as high specific capacitance of 1708 F g^(-1)(850 C g^(-1))at a current density of 1 A g^(-1),good rate capability,and excellent cycling stability.Further,the asymmetric supercapacitor assembled by Co_(3)O_(4)@NiCoLDH_(NSs)and activated carbon,also displays superior electrochemical perfo rmance with high energy density and power density.Remarkably,the strategy of constructing core-shell structure based on MOF templates could be extended to other electrochemical fields.展开更多
Due to the limited electromagnetic wave(EMW)loss capacity and agglomeration,carbon black(CB)gradually fails to meet the increasingly harsh demanding conditions.Herein,defect-rich bamboo-like carbon nanotubes(CNTs)were...Due to the limited electromagnetic wave(EMW)loss capacity and agglomeration,carbon black(CB)gradually fails to meet the increasingly harsh demanding conditions.Herein,defect-rich bamboo-like carbon nanotubes(CNTs)were grown on CB by the process of chemical vapor deposition.CNTs prepared in situ on CB can assist it to build a developed multilevel conductive network and introduce plentiful CB/CNTs nano-interfaces.What’s more,the defects that accompany the growth of CNTs endow CNTs with a moderate conductivity and good impedance matching,thereby causing an effective microwave absorption(MA).Meanwhile,the high-density defects on CNTs can induce dipole polarization to further strengthen the EMW loss ability.The influence of CNTs with different growth time on MA performance has been explored.Profiting from the structural merits,the synthesized CB-CNT with CNTs growth time of 40 min exhibits the optimal absorbing property,which has the minimum reflection loss of-53.6 d B and maximum effective absorption bandwidth of 4.1 GHz with the thickness of 2.7 mm,covering almost the entire X band.The introduction of defect-rich CNTs significantly enhances the EMW loss ability of CB,which provides a rational strategy for the design of high-efficient microwave absorption materials.展开更多
SiC nanowires/pyrocarbon(SiCnws/PyC)core-shell structure toughenedC/C-ZrC-SiC composites were fabricated by CLVD process,and the influences of PyC shell thickness on the microstructure and ablation resistance of the c...SiC nanowires/pyrocarbon(SiCnws/PyC)core-shell structure toughenedC/C-ZrC-SiC composites were fabricated by CLVD process,and the influences of PyC shell thickness on the microstructure and ablation resistance of the composites were researched.The results presented that SiCnws/PyC core-shell structure had a linear shape,and the composites became dense with the increasing PyC thickness.When the thickness of PyC shell increased from 0 to 2.4μm,the density and thermal conductivity of the composites was improved gradually,but the coefficient of thermal expansion(CTE)decreased firstly and then increased.After the ablation test for 90 s,the ablation rates of the composites decreased continuously as the PyC thickness increased from 0 to 1.4μm,but increased when the PyC thickness was up to 2.4μm.Especially when the PyC thickness was 1.4μm,the linear and mass ablation rates of the composites were 71.25%and 63.01%lower than those of the composites without PyC shell.The reasons behind the remarkable improvement of anti-ablation property were that the proper PyC thickness could alleviate the CTE mismatch to promote the formation of complete oxide coating,improve the thermal conductivity to reduce heat corrosion and enhance the capability to limit the mechanical erosion.展开更多
Carbon fiber reinforced carbon composites(C/Cs),are the most promising high-temperature materials and could be widely applied in aerospace and nucleation fields,owing to their superior performances.However,C/Cs are ve...Carbon fiber reinforced carbon composites(C/Cs),are the most promising high-temperature materials and could be widely applied in aerospace and nucleation fields,owing to their superior performances.However,C/Cs are very susceptible to destructive oxidation and thus fail at elevated temperatures.Though matrix modification and coating technologies with Si-based and ultra-high temperature ceramics(UHTCs)are valid to enhance the oxidation/ablation resistance of C/Cs,it’s not sufficient to satisfy the increasing practical applications,due to the inherent brittleness of ceramics,mismatch issues between coatings and C/C substrates,and the fact that carbonaceous matrices are easily prone to high-temperature oxidation.To effectively solve the aforementioned problems,micro/nano multiscale reinforcing strategies have been developed for C/Cs and/or the coatings over the past two decades,to fabricate C/Cs with high strength and excellent high-temperature stability.This review is to systematically summarize the most recent major and important advancements in some micro/nano multiscale strategies,including nanoparticles,nanowires,carbon nanotubes/fibers,whiskers,graphene,ceramic fibers and hybrid micro/nano structures,for C/Cs and/or the coatings,to achieve high-temperature oxidation/ablation-resistant C/Cs.Finally,this review is concluded with an outlook of major unsolved problems,challenges to be met and future research advice for C/Cs with excellent comprehensive mechanical-thermal performance.It’s hoped that a better understanding of this review will be of high scientific and industrial interest,since it provides unusual and feasible new ideas to develop potential and practical C/Cs with improved high-temperature mechanical and oxidation/ablation-resistant properties.展开更多
To prevent the C/C composites from ablation, HfC-HfO2 protective coating was prepared by supersonic atmospheric plasma spraying. The morphology and microstructure of HfC-HfO2 coating were characterized by X-ray diffra...To prevent the C/C composites from ablation, HfC-HfO2 protective coating was prepared by supersonic atmospheric plasma spraying. The morphology and microstructure of HfC-HfO2 coating were characterized by X-ray diffraction and scanning electron microscopy. The ablation resistance test was carried out by an oxyacetylene torch. The results show that the as-prepared coating is dense with little pinholes and crack free. The elements Hf, C and O were uniformly distributed in the cross-section. After ablation for different time, the mass ablation rate fluctuated along with the change of ablation time. The ablation process of the surface coating could be divided into rapid oxidation and solid state sintering stages. During ablation, an Hf CxOy-HfO2 transitional layer was generated in the coating, which resulted from the active oxidation of Hf C. After cooling, some microcracks were observed on the surface of coating, and the structure of cross-section was broken, which were due to the phase transition of HfO2.展开更多
Lightweight,flexible,ultrahigh-performance electromagnetic-interfe rence(EMI)shielding materials are urgently required in the areas of aircraft/aerospace,portable and wearable electronics.Herein,1 D carbon nanotubes(C...Lightweight,flexible,ultrahigh-performance electromagnetic-interfe rence(EMI)shielding materials are urgently required in the areas of aircraft/aerospace,portable and wearable electronics.Herein,1 D carbon nanotubes(CNT)and carbon nanofibers(CNF)with 2 D edge-rich graphene(ERG)are used to form a lightweight,flexible CNT-ERG-CNF hybrid foam.This foam was fabricated through a self-sacrificial templating chemical vapor deposition process,where nanocarbons bond through covalent bonding,forming a hierarchical 3 D hybridized carbon nanostructure.Multistage conductive networks and heterogeneous interfaces were constructed using edge-rich nanocarbons to increase the induced currents and interfacial polarization which makes great contributions to achieve high absorption electromagnetic shielding effectiveness(SEA).The CNT-ERG-CNF hybrid foam exhibits EMI shielding effectiveness(SE)exceeding55.4 dB in the X-band while the specific SE(SSE,SE divided by mass density)achieves 9200 dB cm^(3)g^(-1),which surpasses that of nearly all other carbon-based composite materials.Furthermore,the structural stability and durability of the flexible CNT-ERG-CNF hybrid foams is examined by measuring EMI SE after 10000 times cyclic bending.Remarkably,this work not only provides a new idea for preparing hierarchical carbon materials for a wide range of applications,but presents some fundamental insights for achieving higher absorption losses in EMI shielding materials.展开更多
基金Supported by the National Natural Science Foundation of China(No.U21A6001)the Guangdong Natural Science Foundation Youth Enhancement Program(No.2024A1515030206)the China Meteorological Administration Climate Change Special Program(No.QBZ202301)。
文摘Both natural and human-induced disturbances affect the normal functioning and services of mangrove ecosystems.To address the consequences of intense human and climatic disturbances on sedimentation and carbon burial,sediment cores from the last remaining mangrove Kandelia obovata forest and an adjacent mudflat in the densely populated and typhoon-prone Zhujiang(Pearl)River estuary of China,were analyzed using methods including^(210)Pb dating andδ^(13)C analysis.Results indicate that after damming in the 1950s,during 1960-1980,the natural establishment of K.obovata forests initiated the insitu sedimentation.As these forests matured during 1980-1990,they significantly boosted siltation in the region on mudflat.During 1990-2015,the invasion of Spartina alterniflora and land reclamation for aquaculture caused infiltration of coarse sediments and the impacts of typhoons were recorded within the K.obovata forest,while no clear typhoon record was observed on the mudflat.Since 2015,reforestation efforts with S.apetala that began in 1999 have reversed the effects of earlier deforestation.Over time,mangroves established a rapid autochthonous carbon burial that grew as the forests age,potentially surpassing the influx of allochthonous carbon due to deforestation.The reforestation also immediately improved carbon burial on the mudflat,which stabilized after a decade due to the rapid growth and high biomass of S.apetala.Overall,the K.obovata forest demonstrated a stronger sedimentation and carbon burial capabilities than the mudflat,with a surplus of 35.2 Mg C/hm^(2)in soil organic carbon stock and 1.0 Mg C/(hm^(2)·a)in burial rate.Organic matter dissolved in soil was mainly humus-like components,and mangrove inputs likely increased the degree of humification.This study offered direct evidence regarding the impact of multiple disturbances on local and regional sedimentation and carbon burial,and future management strategies.
基金Supported by National Natural Science Foundation of China(42067009)Scientific Research Project of Yunnan Provincial Department of Education(2024Y742,2023Y0863)+2 种基金Project of Kunming Municipal Commission of Development and Reform(Kunming Spring City Industrial Technology Leading Talents)Science and Technology Major Project of Yunnan Province Science and Technology Department(202202AE090015-02)Yunnan Students’innovation and entrepreneurship training program(S202311393044,S202311393061)。
文摘Continuous cropping has become a common form of agricultural production at present, but with the increase of continuous cropping years, continuous cropping obstacles such as soil-borne diseases and plant growth potential decline are becoming more and more common. At present, the causes of continuous cropping obstacles and continuous cropping restoration have become a hot issue in agricultural research. This paper summarized the effects of continuous cropping obstacles on soil microbial community structure and main technical methods to repair continuous cropping obstacles, such as agricultural measure management, microbial balance adjustment and soil improvement, aiming to provide theoretical reference for protecting the sustainable utilization of soil ecosystem and ensuring the stability of crop production.
基金jointly supported by the National Key Research and Development Plan(Grant No.2023YFB3907405)the National Natural Science Foundation of China(Grant No.42175132)the Chinese Academy of Sciences Project for Young Scientists in Basic Research(Grant No.YSBR-037)。
文摘The challenge of establishing top-down constraints for regional emissions of fossil fuel CO_(2)(FFCO_(2))arises from the difficulty in distinguishing between atmospheric CO_(2)concentrations released from fossil fuels and background variability,particularly owing to the influence of terrestrial biospheric fluxes.This necessitates the development of a regional inversion methodology based on atmospheric CO_(2)observations to verify bottom-up estimations independently.This study presents a promising approach for estimating China's FFCO_(2)emissions by incorporating the model residual errors(MREs)of the column-averaged dry-air mole fractions of CO_(2)(XCO_(2))from FFCO_(2)emissions(MREff)retained in the analysis of natural flux optimization.China's FFCO_(2)emissions during the COVID-19 lockdown in 2020 are estimated using the GEOS-Chem adjoint model.The relationship between the MREff and FFCO_(2)is determined using the model based on a regional FFCO_(2)anomaly suggested by posterior NOx emissions from air-quality data assimilation.The MREff is typically one-tenth in magnitude,but some positively skewed outliers exceed 1 ppm because the prior emissions lack lockdown impacts,thereby exerting considerable observation forcing given the satellite retrieval uncertainties.We initialize the FFCO_(2)with posterior NOx emissions and optimize the colinear emission ratio.Synthetic data experiments demonstrate that this approach reduces the FFCO_(2)bias to less than 10%.The real-data experiments estimate 19%lower FFCO_(2)with GOSAT XCO_(2)and 26%lower with OCO-2 XCO_(2)than the bottom-up estimations.This study proves the feasibility of our regional FFCO_(2)inversion,highlighting the importance of addressing the outlier behaviors observed in satellite XCO_(2)retrievals.
基金supported by the National Natural Science Foundation of China(Nos.52293371,52222204 and 52172103).
文摘Isotropic pyrolytic carbon(IPC)is renowned for its robust mechanical,biological,and tribological prop-erties.However,the current mechanisms for modulating IPC microstructure are insufficient to achieve higher performance.Herein,this study provides nanoscale insights into the formation and property reg-ulation of the core-shell structure of the IPC,integrating simulation and experimental approaches.Large-scale reactive molecular dynamics simulations elucidate the microstructural evolution and assembly pro-cesses from precursors to nanoparticles and intertwined graphene networks.Simulation process charac-terization enable versatile adjustment of IPC microstructural features and one-step deposition of hybrid structures with disordered cores and ordered shell layers.Compared to Pyrolytic carbon(PyC)with lam-inated graphene arrangement,the prepared hybrid structure enables rapid assembly of large-size stan-dalone carbon components.Moreover,the hybrid architecture effectively improves the core-shell phase connection and significantly increases the interfacial shear stress within the intertwined graphene shell layers.Consequently,it greatly improves load transfer efficiency and enhances crack-bridging toughening effect.The endeavor to establish precise microstructure formation and property regulation in IPC materi-als promises to steer high-performance carbon materials toward distinct developmental trajectories.
文摘Carbon nanotubes(CNTs)hold immense promise for a wide array of applications due to their exceptional physical and chemical properties.Understanding and controlling their structural characteristics,particu-larly the diameter and number of walls,is crucial for harnessing their full potential.We investigated the relationship between these parameters for both commercially available and lab-scale CNTs,spanning a wide range of outer diameters(1-13 nm)and numbers of walls(1-13).Our findings revealed a com-monality among the structural diversity,rather than a random distribution,as evidenced by a piecewise linear relationship between the outer diameter and number of walls,with an inflection point occurring at approximately 4 nm in diameter.This observation is unexpected,as the CNTs were synthesized using different approaches and growth conditions;yet,as a group,they exhibit a“structural scaling”.Addi-tionally,we made an intriguing observation:despite increases in outer diameter and number of walls,the inner diameters remained relatively constant(4-5 nm)for thicker CNTs with more than three walls.These results suggest that structural properties can be estimated based on diameter,which not only ad-vances our fundamental understanding of CNT synthesis but also provides practical insights for tailoring CNT properties for various applications.
基金supported by National Natural Science Foundation of China(42372148)。
文摘Oxygen isotope(δ^(18)O)of paleolake water is a key indicator for reconstructing the formation temperature and diagenetic history of lacustrine carbonate minerals.In this study,we use clumped isotopes(Δ_(47))of lacustrine shell limestones to determine the surface erosion thickness and δ^(18)O of Early Jurassic lake water in the northern Sichuan Basin.We analyzed nine shell limestone and seventeen shale samples from the Early Jurassic Da'anzhai Member(J_(1)z^(4))in the Yuanba area.Whether the shell's shapes are well or partially preserved,the J_(1)z^(4)shell limestones in the Yuanba area show no significant recrystallization and dull cathodoluminescence.These characteristics suggest that the shell limestones did not undergo significant diagenetic alteration during late burial.The Δ_(47)values of the J_(1)z^(4)shell limestones range from 0.448±0.005‰to 0.463±0.006‰,yielding clumped isotope temperature(T_(Δ47))of 64.4±0.8 to 69.7±1.4℃,which is significantly higher than the Early Jurassic paleotemperature.It suggests that the Δ_(47)of shell limestones was altered by solid-state reordering,meaning the T_(Δ47)does not reflect the initial formation temperatures.By integrating organic matter's maturation model(Easy%R_(o))of coexisting shales with Δ_(47)solid-state reordering model of calcite,we constrained the maximum burial temperature(~170℃)and the initial formation temperature(~28℃)of these shell limestones.Based on reported paleotemperature gradient,we estimated that the surface erosion thickness was about 1500 m.Furthermore,using the determined initial formation temperatures and conventional oxygen isotope thermometer,we determined that the δ^(18)O values of the Early Jurassic lake water in the Sichuan Basin,which ranged from-10.8‰to-8.0‰(SMOW).The reconstructed paleo temperature and δ^(18)O of lake water suggest that the Early Jurassic in the Sichuan Basin was warm and humid,which was favorable for the deposition of organic-rich lacustrine shale.The methods developed in this study,which employ Δ_(47)of shell limestones to reconstruct the maximum burial temperature and paleolake environmental conditions,demonstrate broad applicability to the Sichuan Basin and similar lacustrine basins.
基金Supported by National Natural Science Foundation of China(Grant Nos.52575091,U2341231)。
文摘With the swift advancement of industrial automation,robots have emerged as an essential component in emerging industries and high-end equipment,thereby propelling industrial production towards greater intelligence and efficiency.This paper reviews the pivotal technologies for motion planning of robots engaged in contact tasks within industrial automation contexts,encompassing environmental recognition,trajectory generation strategies,and sim-to-real transfer.Environmental recognition technology empowers robots to accurately discern objects and obstacles in their operational environment.Trajectory generation strategies formulate optimal motion paths based on environmental data and task specifications.Sim-to-real transfer is committed to effectively translating strategies from simulated environments to actual production,thereby diminishing the discrepancies between simulation and reality.The article also delves into the application of artificial intelligence in robot motion planning and how embodied intelligence models catalyze the evolution of robotics technology towards enhanced intelligence and automation.The paper concludes with a synthesis of the methodologies addressing this challenge and a perspective on the myriad challenges that warrant attention.
基金supported by the National Key Research and Development Program of China(Grant 2021YFA0715600,2021YFA0717700,2018YFB2202900)National Natural Science Foundation of China(52192610,62274127,62374128)+5 种基金the Fundamental Research Funds for the Central Universities,2023 Qinchuangyuan Construction Two Chain Integration Special Project(23LLRH0043)Key Research and Development Program of Shaanxi Province(Grant 2024GX-YBXM-512)Foundation of Zhejiang Provincial Key Lab of Solar Energy Utilization&Energy Saving Technology(ZJS-OP-2020-11)GuangDong Basic and Applied Basic Research Foundation(Grant 2022A1515111220)the fund of the state Key Laboratory of Solidification Processing in NPU(Grant No.SKLSP202317)Young Elite Scientists Sponsorship Program by CAST,Doctoral Student Special Plan.
文摘One of the significant technological challenges in safeguarding electronic devices pertains to the modulation of electromagnetic(EM)wave jamming and the recycling of defensive shields.The synergistic effect of heterodimensional materials can effectively enable the manipulation of EM waves by altering the nanostructure.Here we propose a novel approach for upcycling by-products of silver nanowires that can fabricate shape-tunable aerogels which enable the modulation of its interaction with microwaves by heterodimensional structure of byproducts.By-product heterodimensionality was used to design EM-wave-jamming-dissipation structures and therefore two typical tunable aerogel forms were studied.The first tunable form was aerogel film,which shielded EM interference(EMI shielding effectiveness(EMI SE)>89 dB)and the second tunable form was foam,which performed dual EM functions(SE>30 dB&reflective loss(RL)<-35 dB,effective absorption bandwidth(EAB)>6.7 GHz).We show that secondary recycled aerogels retain nearly all of their EM protection properties,making this type of closed-loop cycle an appealing option.Our findings pave the way for the development of adaptive EM functions with nanoscale regulation in a green and closed-loop cycle,and they shed light on the fundamental understanding of microwave interactions with heterodimensional structures.
基金supported by the FengYun Application Pioneering Project (Grant No. FY-APP-2022.0502)the National Natural Science Foundation of China (42205140)the State Key Laboratory of Atmospheric Environment end Extreme Meteorology (Grant No. 2024QN04)
文摘The Hyperspectral Infrared Atmospheric Sounder-II(HIRAS-II)onboard China’s FungYun(FY)-3F meteorological satellite was launched in August 2023.This study presents the first attempt to retrieve the global carbon monoxide(CO)column from HIRAS-II/FY-3F spectra based on a newly established full-physics algorithm.The CO global columns derived from the HIRAS-II/FY-3F satellite are compared to measurements from the Infrared Atmospheric Sounding Interferometer(IASI)onboard Europe’s MetopB satellite,as both satellites have the same spectral range with a similar overpass time.The correlation coefficient between the IASI/Metop-B and HIRAS-II/FY-3F CO retrievals is about 0.8.The HIRAS-II/FY-3F satellite can capture well the regions with high CO values,e.g.,Africa,North America,and East Asia.The relative difference in the CO global column between HIRAS-II and IASI is 1.2±13.7(1)%,which is within their combined retrieval uncertainty.The CO plumes from the fire emissions in North America between 18 and 23 July 2024 were observed by the HIRAS-II/FY-3F satellite and consistent with the CAMS(Copernicus Atmosphere Monitoring Service)model simulations.Our results show that the HIRAS-II/FY-3F spectra are of good enough quality to provide quantitative observations of global CO column remote sensing observations.
基金the supercomputing center of USTC for their strong supportsupported by the National Key R&D Program of China(Grant Nos.2023YFA1609400,2023YFA1606703,2020YFA0406400,and 2020YFA0406300)+3 种基金the International Partnership Program of the Chinese Academy of Sciences(Grant No.211134KYSB20200057)the National Natural Science Foundation of China(Grant Nos.12035013,12061131003,12122509,12105276,11625523,12405091,12235018,and 12435007)the CAS Youth Team Program(Grant No.YSBR-101)the Natural Science Foundation of Guangxi Province,China(Grant No.2025GXNSFBA069314)。
文摘Weak radiative hyperon decays represent a rich interplay between weak interactions and the internal structure of baryons,offering profound insights into Quantum Chromodynamics and weak interactions.Recent experimental observations,particularly from BESIII,have revealed deviations from theoretical predictions.These deviations could signal new physics or the need for refined theoretical models incorporating intermediate resonance effects.This review discusses recent theoretical advancements and key experimental findings,focusing on recent measurements from BESIII and their implications for strong interactions and baryon structure.
基金supported by the the National Key R&D Program of China(Grant Nos.2022YFA1604900 and 2023YFA1606703)the National Natural Science Foundation of China(Grant Nos.12025501,12435007,12405133,and 12347180)+1 种基金China Postdoctoral Science Foundation(Grant No.2023M740189)the Postdoctoral Fellowship Program of CPSF(Grant No.GZC20233381).
文摘Hypernuclei,nuclei containing one or more hyperons,serve as unique laboratories for probing the non-perturbative quantum chromodynamics(QCD).Recent progress in hypernuclear physics,driven by advanced experimental techniques and theoretical innovations,is briefly reviewed with a focus on key findings and unresolved challenges,such as the precise determination of the hypertriton binding energy,investigations of charge symmetry breaking in mirror hypernuclei,and the search for exotic systems,including the neutral nnΛstate.Experimental breakthroughs,including invariant-mass analyses and femtoscopy studies in heavy-ion collisions,as well as high-resolutionγ-spectroscopy,have enabled precise studies of light hypernuclei and offered critical insights into the hyperon–nucleon interaction.Theoretical progress,including ab initio calculations based on chiral effective field theory and lattice QCD,has further enhanced our understanding of hyperon–nucleon and hyperon–hyperon interactions.
文摘Accurate acid placement constitutes a major concern in matrix stimulation because the acid tends to penetrate the zones of least resistance while leaving the low-permeability regions of the formation untreated.Degradable materials(fibers and solid particles)have recently shown a good capability as fluid diversion to overcome the issues related to matrix stimulation.Despite the success achieved in the recent acid stimulation jobs stemming from the use of some products that rely on fiber flocculation as the main diverting mechanism,it was observed that the volume of the base fluid and the loading of the particles are not optimized.The current industry lacks a scientific design guideline because the used methodology is based on experience or empirical studies in a particular area with a particular product.It is important then to understand the fundamentals of how acid diversion works in carbonates with different diverting mechanisms and diverters.Mathematical modeling and computer simulations are effective tools to develop this understanding and are efficiently applied to new product development,new applications of existing products or usage optimization.In this work,we develop a numerical model to study fiber dynamics in fluid flow.We employ a discrete element method in which the fibers are represented by multi-rigid-body systems of interconnected spheres.The discrete fiber model is coupled with a fluid flow solver to account for the inherent simultaneous interactions.The focus of the study is on the tendency for fibers to flocculate and bridge when interacting with suspending fluids and encountering restrictions that can be representative of fractures or wormholes in carbonates.The trends of the dynamic fiber behavior under various operating conditions including fiber loading,flow rate and fluid viscosity obtained from the numerical model show consistency with experimental observations.The present numerical investigation reveals that the bridging capability of the fiber–fluid system can be enhanced by increasing the fiber loading,selecting fibers with higher stiffness,reducing the injection flow rate,reducing the suspending fluid viscosity or increasing the attractive cohesive forces among fibers by using sticky fibers.
基金supported by the National Natural Science Foundation of China (Grant Nos. 51221001 and 51272213)the Foundation for the Author of National Excellent Doctoral Dissertation of China 201036+1 种基金the Research Fund of State Key Laboratory of Solidification Processing (NWPU), China (Grant No. 25-TZ-2009)the "111" Project (Grant No. B08040)
文摘C/C-ZrC composites with continuous ZrC matrix were prepared by precursor infiltration and pyrolysis process using zirconium-containing polymer.Ablation properties of the composites were investigated by oxyacetylene flame with heat flux of 2380 and 4180 kW/m2,respectively.The results showed that C/C-ZrC composites exhibited excellent ablation resistance under the heat flux of 2380 kW/m2for 120 s and a tree-coral-like ZrO2protective layer formed after ablation.However,when the heat flux increased to 4180 kW/m2,the maximum temperature of ablated surface reached 2500 ℃ and a strong degradation of ablation resistance was observed due to the weak bonding between the formed ZrO2layer and the composites.The flexural strength of C/C-ZrC composites was 110.7 ± 7.5 MPa.There were a large number of carbon fiber bundles pull-out,and the composites exhibited a pseudo-plastic fracture behavior.
基金financially supported by the National Natural Science Foundation of China(Nos.50832004 and 50972120)the 111 Project(No.B08040)
文摘To effectively get the thermal expansion coef- ficient （CTE） of three-dimensional （3D） braided C/C composites and study the variations, a VC＋＋ program with graphical user interfaces was obtained, based on the yam unit model and numerical analysis. With the limited basic properties of carbon fibers and carbon matrix, CTE of 3D braided C/C composites is obtained at 85 ~C. The deviation between the simulated and exl^erimental axial CTE of 3D braided C/C composites is no more than 11%. The effects of different parameters （including the braiding angle of 3D braided preform, the fiber volume fraction and the porosity of 3D braided C/C composites, and the elastic modulus, Poisson＇s ratio and CTEs of carbon fibers and carbon matrix） were analyzed with the program. The results show that the axial CTE of C/C composites decreases with the increase of the braiding angle, the fiber volume fraction, and the porosity of 3D braided C/C composites. The transverse elastic modulus of carbon fibers has the greatest effect on the axial CTE among the studied mechanical parameters, followed by the elastic modulus and Poisson＇s ratio of carbon matrix.
基金financial support from the National Natural Science Foundation of China(Grant No.51821091,51872234)the Natural Science Foundation of Shaanxi Province(2018JM5044)。
文摘Hierarchical Co_(3)O_(4)@NiCoLDH nanosheets(NSs)were prepared on carbon cloth through a multistep method,containing Metal-organic frameworks(MOF)-templated thermal annealing and electrodeposition.The triangle-shaped Co_(3)O_(4 NSs)were firstly obtained by thermal treatment of MOF templates in air.Then,ultrathin NiCoLDH_(NSs)were in-situ electrodeposited on the surface of Co_(3)O_(4NSs),constructing a core-shell structure.Benefiting the unique hierarchical structure,high conductivity of Co_(3)O_(4 NSs)core and large surface area of NiCoLDHNSs shell,the Co_(3)O_(4)@NiCoLDH_(NSs)array served as supercapacitor electrode exhibits excellent electrochemical properties,such as high specific capacitance of 1708 F g^(-1)(850 C g^(-1))at a current density of 1 A g^(-1),good rate capability,and excellent cycling stability.Further,the asymmetric supercapacitor assembled by Co_(3)O_(4)@NiCoLDH_(NSs)and activated carbon,also displays superior electrochemical perfo rmance with high energy density and power density.Remarkably,the strategy of constructing core-shell structure based on MOF templates could be extended to other electrochemical fields.
基金financially supported by National Natural Science Foundation of China(52072304,52172103)Natural Science Basic Research Plan in Shaanxi(2022JC-25)+1 种基金the Key R&D Program of Shaanxi Provence(2019ZDLGY04-02)China Postdoctoral Science Foundation(2021M702659)。
文摘Due to the limited electromagnetic wave(EMW)loss capacity and agglomeration,carbon black(CB)gradually fails to meet the increasingly harsh demanding conditions.Herein,defect-rich bamboo-like carbon nanotubes(CNTs)were grown on CB by the process of chemical vapor deposition.CNTs prepared in situ on CB can assist it to build a developed multilevel conductive network and introduce plentiful CB/CNTs nano-interfaces.What’s more,the defects that accompany the growth of CNTs endow CNTs with a moderate conductivity and good impedance matching,thereby causing an effective microwave absorption(MA).Meanwhile,the high-density defects on CNTs can induce dipole polarization to further strengthen the EMW loss ability.The influence of CNTs with different growth time on MA performance has been explored.Profiting from the structural merits,the synthesized CB-CNT with CNTs growth time of 40 min exhibits the optimal absorbing property,which has the minimum reflection loss of-53.6 d B and maximum effective absorption bandwidth of 4.1 GHz with the thickness of 2.7 mm,covering almost the entire X band.The introduction of defect-rich CNTs significantly enhances the EMW loss ability of CB,which provides a rational strategy for the design of high-efficient microwave absorption materials.
基金financial support of the project from the National Natural Science Foundation of China(No.51821091 and 51872233)the Research Foundation of Chengdu University of Technology(No.10912-KYQD202008264)。
文摘SiC nanowires/pyrocarbon(SiCnws/PyC)core-shell structure toughenedC/C-ZrC-SiC composites were fabricated by CLVD process,and the influences of PyC shell thickness on the microstructure and ablation resistance of the composites were researched.The results presented that SiCnws/PyC core-shell structure had a linear shape,and the composites became dense with the increasing PyC thickness.When the thickness of PyC shell increased from 0 to 2.4μm,the density and thermal conductivity of the composites was improved gradually,but the coefficient of thermal expansion(CTE)decreased firstly and then increased.After the ablation test for 90 s,the ablation rates of the composites decreased continuously as the PyC thickness increased from 0 to 1.4μm,but increased when the PyC thickness was up to 2.4μm.Especially when the PyC thickness was 1.4μm,the linear and mass ablation rates of the composites were 71.25%and 63.01%lower than those of the composites without PyC shell.The reasons behind the remarkable improvement of anti-ablation property were that the proper PyC thickness could alleviate the CTE mismatch to promote the formation of complete oxide coating,improve the thermal conductivity to reduce heat corrosion and enhance the capability to limit the mechanical erosion.
基金supported by the National Natural Science Foundation of China(Nos.91860203,51821091,51872239,52002321 and 52061135102)the China Postdoctoral Science Foundation(No.2019M660265)+3 种基金the Fundamental Research Funds for the Central Universities(China,Nos.G2019KY05116,G2020KY05125)the Innovation Talent Promotion Plan of Shaanxi Province for Science and Technology Innovation Team(No.2020TD003)the Creative Research Foundation of Science and Technology on Thermostructural Composite Materials Laboratory(Nos.614291102010517,5050200015 and 5150200033)the Shaanxi Provincial Education Department of China(No.2020JQ-170)。
文摘Carbon fiber reinforced carbon composites(C/Cs),are the most promising high-temperature materials and could be widely applied in aerospace and nucleation fields,owing to their superior performances.However,C/Cs are very susceptible to destructive oxidation and thus fail at elevated temperatures.Though matrix modification and coating technologies with Si-based and ultra-high temperature ceramics(UHTCs)are valid to enhance the oxidation/ablation resistance of C/Cs,it’s not sufficient to satisfy the increasing practical applications,due to the inherent brittleness of ceramics,mismatch issues between coatings and C/C substrates,and the fact that carbonaceous matrices are easily prone to high-temperature oxidation.To effectively solve the aforementioned problems,micro/nano multiscale reinforcing strategies have been developed for C/Cs and/or the coatings over the past two decades,to fabricate C/Cs with high strength and excellent high-temperature stability.This review is to systematically summarize the most recent major and important advancements in some micro/nano multiscale strategies,including nanoparticles,nanowires,carbon nanotubes/fibers,whiskers,graphene,ceramic fibers and hybrid micro/nano structures,for C/Cs and/or the coatings,to achieve high-temperature oxidation/ablation-resistant C/Cs.Finally,this review is concluded with an outlook of major unsolved problems,challenges to be met and future research advice for C/Cs with excellent comprehensive mechanical-thermal performance.It’s hoped that a better understanding of this review will be of high scientific and industrial interest,since it provides unusual and feasible new ideas to develop potential and practical C/Cs with improved high-temperature mechanical and oxidation/ablation-resistant properties.
基金supported by the National Natural Science Foundation of China under Grant Nos. U1435202 and 51521061the “111” Project under Grant No. 08040the Research Fund of the State Key Laboratory of Solidification Processing (Northwestern Polytechnical University), China (Grant No. 142-TZ-2016)
文摘To prevent the C/C composites from ablation, HfC-HfO2 protective coating was prepared by supersonic atmospheric plasma spraying. The morphology and microstructure of HfC-HfO2 coating were characterized by X-ray diffraction and scanning electron microscopy. The ablation resistance test was carried out by an oxyacetylene torch. The results show that the as-prepared coating is dense with little pinholes and crack free. The elements Hf, C and O were uniformly distributed in the cross-section. After ablation for different time, the mass ablation rate fluctuated along with the change of ablation time. The ablation process of the surface coating could be divided into rapid oxidation and solid state sintering stages. During ablation, an Hf CxOy-HfO2 transitional layer was generated in the coating, which resulted from the active oxidation of Hf C. After cooling, some microcracks were observed on the surface of coating, and the structure of cross-section was broken, which were due to the phase transition of HfO2.
基金financial supports of this work by National Natural Science Foundation of China(51821091,51872234)Natural Science Basic Research Plan in Shaanxi(No.2020JQ-154)。
文摘Lightweight,flexible,ultrahigh-performance electromagnetic-interfe rence(EMI)shielding materials are urgently required in the areas of aircraft/aerospace,portable and wearable electronics.Herein,1 D carbon nanotubes(CNT)and carbon nanofibers(CNF)with 2 D edge-rich graphene(ERG)are used to form a lightweight,flexible CNT-ERG-CNF hybrid foam.This foam was fabricated through a self-sacrificial templating chemical vapor deposition process,where nanocarbons bond through covalent bonding,forming a hierarchical 3 D hybridized carbon nanostructure.Multistage conductive networks and heterogeneous interfaces were constructed using edge-rich nanocarbons to increase the induced currents and interfacial polarization which makes great contributions to achieve high absorption electromagnetic shielding effectiveness(SEA).The CNT-ERG-CNF hybrid foam exhibits EMI shielding effectiveness(SE)exceeding55.4 dB in the X-band while the specific SE(SSE,SE divided by mass density)achieves 9200 dB cm^(3)g^(-1),which surpasses that of nearly all other carbon-based composite materials.Furthermore,the structural stability and durability of the flexible CNT-ERG-CNF hybrid foams is examined by measuring EMI SE after 10000 times cyclic bending.Remarkably,this work not only provides a new idea for preparing hierarchical carbon materials for a wide range of applications,but presents some fundamental insights for achieving higher absorption losses in EMI shielding materials.
