We prove that a Cl-generic volume-preserving dynamical system （diffeomor- phism or flow） has the shadowing property or is expansive or has the weak specification property if and only if it is Anosov. Finally, as in ...We prove that a Cl-generic volume-preserving dynamical system （diffeomor- phism or flow） has the shadowing property or is expansive or has the weak specification property if and only if it is Anosov. Finally, as in [10, 27], we prove that the Cl-robustness, within the volume-preserving context, of the expansiveness property and the weak specifica- tion property, imply that the dynamical system （diffeomorphism or flow） is Anosov.展开更多
In this paper,forward expansiveness and entropies of"subsystems"2)of Z^(k)_(+)-actions are investigated.Letαbe a Z^(k)_(+)-action on a compact metric space.For each 1≤j≤k-1,denote G^(j)_(+)={V+:=V∩R^(k)_...In this paper,forward expansiveness and entropies of"subsystems"2)of Z^(k)_(+)-actions are investigated.Letαbe a Z^(k)_(+)-action on a compact metric space.For each 1≤j≤k-1,denote G^(j)_(+)={V+:=V∩R^(k)_(+):V is a j-dimensional subspace of R^(k)}.We consider the forward expansiveness and entropies forαalong V+∈G^(j)_(+).Adapting the technique of"coding",which was introduced by M.Boyle and D.Lind to investigate expansive subdynamics of Z^(k)-actions,to the Z^(k)_(+)cases,we show that the set E^(j)_(+)(α)of forward expansive j-dimensional V_(+)is open in G^(j)_(+).The topological entropy and measure-theoretic entropy of j-dimensional subsystems ofαare both continuous in E^(j)_(+)(α),and moreover,a variational principle relating them is obtained.For a 1-dimensional ray L∈G^(+)_(1),we relate the 1-dimensional subsystem ofαalong L to an i.i.d.random transformation.Applying the techniques of random dynamical systems we investigate the entropy theory of 1-dimensional subsystems.In particular,we propose the notion of preimage entropy(including topological and measure-theoretical versions)via the preimage structure ofαalong L.We show that the preimage entropy coincides with the classical entropy along any L∈E1+(α)for topological and measure-theoretical versions respectively.Meanwhile,a formula relating the measure-theoretical directional preimage entropy and the folding entropy of the generators is obtained.展开更多
We investigate the null tests of cosmic accelerated expansion by using the baryon acoustic oscillation(BAO)data measured by the dark energy spectroscopic instrument(DESI)and reconstruct the dimensionless Hubble parame...We investigate the null tests of cosmic accelerated expansion by using the baryon acoustic oscillation(BAO)data measured by the dark energy spectroscopic instrument(DESI)and reconstruct the dimensionless Hubble parameter E(z)from the DESI BAO Alcock-Paczynski(AP)data using Gaussian process to perform the null test.We find strong evidence of accelerated expansion from the DESI BAO AP data.By reconstructing the deceleration parameter q(z) from the DESI BAO AP data,we find that accelerated expansion persisted until z■0.7 with a 99.7%confidence level.Additionally,to provide insights into the Hubble tension problem,we propose combining the reconstructed E(z) with D_(H)/r_(d) data to derive a model-independent result r_(d)h=99.8±3.1 Mpc.This result is consistent with measurements from cosmic microwave background(CMB)anisotropies using the ΛCDM model.We also propose a model-independent method for reconstructing the comoving angular diameter distance D_(M)(z) from the distance modulus μ,using SNe Ia data and combining this result with DESI BAO data of D_(M)/r_(d) to constrain the value of r_(d).We find that the value of r_(d),derived from this model-independent method,is smaller than that obtained from CMB measurements,with a significant discrepancy of at least 4.17σ.All the conclusions drawn in this paper are independent of cosmological models and gravitational theories.展开更多
China’s booming performing arts sector is reshaping cultural experiences and creating vibrant new spaces for leisure,tourism and creativity The year 2025 marked a period of vigorous expansion for China’s performing ...China’s booming performing arts sector is reshaping cultural experiences and creating vibrant new spaces for leisure,tourism and creativity The year 2025 marked a period of vigorous expansion for China’s performing arts sector,as the industry evolved from a traditional entertainment field into a comprehensive engine of cultural consumption.展开更多
There is an urgent need to develop magnesium-matrix materials that exhibit both high thermal conductivity and low thermal expansion to ensure compatibility with chips.This study aims to develop a Mg-Zn-Cu alloy with h...There is an urgent need to develop magnesium-matrix materials that exhibit both high thermal conductivity and low thermal expansion to ensure compatibility with chips.This study aims to develop a Mg-Zn-Cu alloy with high thermal conductivity.Furthermore,it explores the preparation of AlN_(P)/Mg-Zn-Cu composites featuring low coefficients of thermal expansion.The stir casting method was utilized to fabricate the composites and an investigation was conducted to examine their microstructure and thermal properties.Results indicate that the addition of AlN_(P)reduces the thermal expansion coefficient while maintaining relatively high thermal conductivity.Specifically,the AlN_(P)/Mg-0.5Zn-0.5Cu composite with 30wt.%AlN_(P)achieves a thermal conductivity of 132.7 W·m^(-1)·K^(-1)and a thermal expansion coefficient of 18.5×10^(-6)K^(-1),rendering it suitable for electronic packaging applications where thermal management is critical.展开更多
Due to their chiral structure,carbon nanosprings possess unique properties that are promising for nanotechnology applications.The structural transformations of carbon nanosprings in the form of spiral macromolecules d...Due to their chiral structure,carbon nanosprings possess unique properties that are promising for nanotechnology applications.The structural transformations of carbon nanosprings in the form of spiral macromolecules derived from planar coronene and kekulene molecules(graphene helicoids and spiral nanoribbons)are analyzed using molecular dynamics simulations.The interatomic interactions are described by a force field including valence bonds,bond angles,torsional and dihedral angles,as well as van derWaals interactions.While the tension/compression of such nanosprings has been analyzed in the literature,this study investigates other modes of deformation,including bending and twisting.Depending on the geometric characteristics of the carbon nanosprings,the formation of structural and helix reversal topological defects is described.During these structural transformations of the nanosprings,only van der Waals bonds break and recover,but breaking or recovery of covalent bonds does not take place.It is found that nanosprings demonstrate a significantly higher coefficient of axial thermal expansion than many metals and alloys.Under axial compression,Euler instability leads to lateral bending with continuous deformation of the nanospring axis at relatively low compression,while at high compression,bending kinks form.Various types of topological defects form on the instantly released nanospring during its relaxation from a highly stretched configuration.These results are useful for the development of nanosensors operating over a wide temperature range.展开更多
In this paper,we first establish refined versions of the Bohr inequalities for the class of holomorphic functions from the unit ball BX of a complex Banach space X into ℂ.As applications,we will establish refined Bohr...In this paper,we first establish refined versions of the Bohr inequalities for the class of holomorphic functions from the unit ball BX of a complex Banach space X into ℂ.As applications,we will establish refined Bohr inequalities of functional type or of norm type for holomorphic mappings with lacunary series on the unit ball BX with values in higher dimensional spaces.Next,we obtain the Bohr-Rogosinski inequality for the class of holomorphic functions on BX.In addition,we establish an improved version of the Bohr inequality for holomorphic functions on BX.All the results are proved to be sharp.展开更多
Fuel-coolant interaction(FCI)remains one of the most complex challenges in severe accident research,with the triggering process being a key aspect that may govern subsequent fine fragmentation and potential steam expl...Fuel-coolant interaction(FCI)remains one of the most complex challenges in severe accident research,with the triggering process being a key aspect that may govern subsequent fine fragmentation and potential steam explosions.In this study,the evolution characteristics of droplet-water interactions under external disturbance conditions were investigated using a self-designed FCI experimental setup.The experimental observations revealed that cavity formation reduced the drag force on the droplet,thereby increasing its peak velocity.However,the external disturbance pressure can disrupt the cavity,leading to a reduction in the droplet peak velocity.Furthermore,it was found that an increase in external disturbance pressure tended to increase the peak value of the droplet expansion rate,thereby promoting the fine-fragmentation process.This effect holds regardless of the initial droplet temperature,coolant temperature,or even when using droplet materials such as lead,which is generally considered unfavorable for steam explosions.Comparative analyses indicated that a higher external disturbance pressure may shorten the triggering time of the droplet surface and enhance the trigger intensity.These findings provide important phenomenological insights for further investigation of the triggering mechanisms in the initial stage of fuel-coolant interactions.展开更多
Urban spatial morphology(USM)optimization is critical to balancing biodiversity conservation and sustainable urbanization.However,previous studies predominantly focused on the socio-economic efficiency and static ecol...Urban spatial morphology(USM)optimization is critical to balancing biodiversity conservation and sustainable urbanization.However,previous studies predominantly focused on the socio-economic efficiency and static ecological metrics and rarely addressed the dynamic USM optimization across spatial scales.Here,we developed a multi-level ecological network(MEN)framework to resolve the tension between urban expansion and ecological integrity.By integrating the cost-weighted distance analysis with a hierarchical network transmission mechanism,we established a cross-scale spatial optimization system,which coordinated the regional ecological corridors and local habitat patches.Comparative experiments with conventional single-scale approaches and scenario simulations using the PLUS model show that the MEN framework had superior performance in three dimensions:(1)spatial governance:the primary-level network(peri-urban natural reserves)effectively contained urban sprawl,and the secondary-level network(intra-urban green corridors)mitigated habitat fragmentation and improved the built-environment;(2)scenario robustness:the model maintained an optimal compactness-loose balance in multiple development pathways;(3)landscape metrics:patch fragmentation decreased by 18.25%,and the internal landscape richness improved by 10.66%compared to the scenario without USM optimization.The findings provide new insight to establish a hierarchical ecological optimization framework as a nature-based spatial protocol to reconcile metropolitan growth with landscape sustainability.展开更多
In-situ enlargement of super-large-span tunnels can intensify excavation-induced unloading in the surrounding rock,increasing deformation demand and failure risk during construction.This study combines laboratory mode...In-situ enlargement of super-large-span tunnels can intensify excavation-induced unloading in the surrounding rock,increasing deformation demand and failure risk during construction.This study combines laboratory model tests with FLAC3D simulations to evaluate the stabilizing role of prestressed anchor cables and to establish an energy-balance framework for support optimization.Comparative model tests of existing and enlarged tunnel sections,with and without anchors,show that reinforcement increases load-carrying capacity,reduces displacement,and confines damage to more localized zones.The numerical simulations reproduce displacement fields,shear-strain localization,and plastic-zone evolution with good agreement against the experimental observations.The energy framework is implemented in the in-situ simulations by quantifying unloading-related energy release in the rock mass and reinforcement work contributed by the anchors,and by introducing an energy release–reinforcement ratio as a stability indicator.Parametric analyses indicate that anchor length,spacing,and prestress influence stability in a nonlinear manner,with diminishing returns once reinforcement extends beyond the mechanically dominant deformation zone.An efficient parameter window is identified that improves deformation and yielding control while avoiding unnecessary reinforcement.The results provide an energy-consistent and design-oriented basis for prestressed anchorage selection in large-span tunnel expansion.展开更多
The growing demand for land to accommodate renewable energy infrastructure has intensified competition with biodiversity conservation, agriculture, and ecosystem services. In Portugal, electricity system decarbonisati...The growing demand for land to accommodate renewable energy infrastructure has intensified competition with biodiversity conservation, agriculture, and ecosystem services. In Portugal, electricity system decarbonisation relies heavily on utility-scale solar energy(USSE) facilities, yet the spatial extent of land transformation associated with photovoltaic development has not been systematically assessed. This study provides an assessment of the land occupancy of USSE facilities and associated land use and land cover(LULC) changes in continental Portugal over the past two decades, as well as their spatial relationship with areas designated for land and nature conservation. A geospatial database of USSE installations(≥1 MW) was developed through the integration of multiple data sources using geographic information systems(GIS). The geometric consistency of spatial features was ensured through harmonisation and validation procedures involving GIS-based corrections supported by Sentinel-2 satellite imagery. Spatial overlay analyses were conducted with multitemporal LULC datasets and with land-use planning constraints, including areas classified for nature conservation, ecological reserves, and agricultural reserves. The results indicate that USSE deployment has been predominantly located in the southern regions of Portugal, although the location of planned projects indicates a northward shift. The implementation of USSE facilities has been mainly associated with LULC changes in forest land, agricultural areas, pastures and shrubland. Spatial overlaps were observed with areas classified within the national ecological and agricultural reserves.These patterns may be indicative of growing land-use conflicts, but the extent to which these developments align with land-use planning objectives and conservation priorities requires further examination.展开更多
The Saccostrea mordax Gould,1850 is a typical intertidal species,whose genetic differentiation is influenced by various factors,including geological and climatic changes.To explore the genetic structure and historical...The Saccostrea mordax Gould,1850 is a typical intertidal species,whose genetic differentiation is influenced by various factors,including geological and climatic changes.To explore the genetic structure and historical population characteristics of Saccostrea mordax,we sequenced the mitochondrial cytochrome c oxidase subunit I(COI)gene from 58 specimens sampled from four locations in the western Pacific.Additionally,103 individuals from the Persian Gulf and western Pacific(from databases)were included for phylogenetic analysis.The Bayesian Inference tree showed that all specimens were divided into two clades,i.e.,the Persian Gulf population and the western Pacific population.Spatial molecular variance analysis indicated significant genetic differentiation between the two populations,and isolation by distance analysis revealed a positive correlation between genetic differentiation and geographic distance.Neutrality tests and Bayesian Skyline Plot suggested that both populations underwent expansions during the late Pleistocene.This study revealed the population history of Saccostrea mordax and described a new lineage,Saccostrea mordax lineage D,providing a foundation for understanding oyster biodiversity formation and genetic resource conservation.展开更多
The metallic Ni catalyst suffers from strong binding with the*CO intermediate,resulting in poisoning of the catalyst surface.It is feasible to facilitate the generation of CO by alleviating the binding strength of the...The metallic Ni catalyst suffers from strong binding with the*CO intermediate,resulting in poisoning of the catalyst surface.It is feasible to facilitate the generation of CO by alleviating the binding strength of the*CO intermediate on the Ni metal surface through a lattice expansion strategy.Here,Ni_(3)ZnC_(0.7)@C with lattice expansion was synthesized by co-doping with Zn and interstitial C through high-temperature pyrolysis.Structural characterization confirms that the lattice of Ni_(3)ZnC_(0.7)expands by 5.47%compared to Ni due to the co-doping of Zn and interstitial C.The Ni_(3)ZnC_(0.7)@C possesses excellent catalytic performance with Faradaic efficiency(FE)of CO exceeding 90%over a wide potential range from−0.8 to−1.4 V versus reversible hydrogen electrode(vs.RHE)with a peak FECO of 96.6%at−1.0 V vs.RHE.In membrane electrode assembly(MEA)testing,Ni_(3)ZnC_(0.7)@C achieves a FECO of 81.4%at the industrial-level current density of 400 mA cm^(−2).In situ attenuated total reflection surface-enhanced infrared absorption spectroscopy(ATR-SEIRAS)and density functional theory(DFT)calculations reveal that the co-introduction of Zn and interstitial C in the Ni crystal can significantly promote the desorption of*CO intermediate,which facilitates the generation of CO.This study demonstrates a viable way for designing efficient transition metal catalysts for CO_(2)electroreduction through lattice strain engineering.展开更多
Large-scale afforestation and forest conservation policies have been widely implemented in Southwest China over past decades.These efforts have significantly protected the remaining long-established forests in the reg...Large-scale afforestation and forest conservation policies have been widely implemented in Southwest China over past decades.These efforts have significantly protected the remaining long-established forests in the region and greatly expanded forested areas.Utilizing nearly 30 years of satellite time-series data,we reveal that the region’s enhanced carbon sequestration(3×10^(12) g·C annually)is primarily driven by crucial changes in forest structure and age,occurring alongside a nearly 120%increase in forested land area.We observe that dense forests maintain a rapid growth rate of approximately 2.5%annually for carbon sequestration in the initial years after establishment.However,this growth rate decelerates with increasing apparent forest age.Meanwhile,the densification(modeled as an increasing forest probability)rate of forests reaches its peak growth during the 10-20 year period,sustaining a high annual growth rate of about 1.8%.We also find that improvements in forest structure,particularly the increasing of forest canopy density and apparent forest age coupled with a notable reduction in forest fragmentation,are also the main driving factors for the enhanced carbon sequestration capacity.Based on these findings,we conclude that forest restoration policies in Southwest China have been successful not only in facilitating large-scale forest growth in Southwest China but,more critically,in promoting the structural maturation(e.g.,densification and reduced fragmentation)that is essential for enhancing the region’s carbon sink capacity and its resilience.展开更多
Purpose–The bridge expansion joint(BEJ)is a key device for accommodating spatial displacement at the beam end,and for providing vertical support for running trains passing over the gap between the main bridge and the...Purpose–The bridge expansion joint(BEJ)is a key device for accommodating spatial displacement at the beam end,and for providing vertical support for running trains passing over the gap between the main bridge and the approach bridge.For long-span railway bridges,it must also be coordinated with rail expansion joint(REJ),which is necessary to accommodate the expansion and contraction of,and reducing longitudinal stress in,the rails.The main aim of this study is to present analysis of recent developments in the research and application of BEJs in high-speed railway(HSR)long-span bridges in China,and to propose a performance-based integral design method for BEJs used with REJs,from both theoretical and engineering perspectives.Design/methodology/approach–The study first presents a summary on the application and maintenance of BEJs in HSR long-span bridges in China representing an overview of their state of development.Results of a survey of typical BEJ faults were analyzed,and field testing was conducted on a railway cable-stayed bridge in order to obtain information on the major mechanical characteristics of its BEJ under train load.Based on the above,a performance-based integral design method for BEJs with maximum expansion range 1600 mm(±800 mm),was proposed,covering all stages from overall conceptual design to consideration of detailed structural design issues.The performance of the novel BEJ design thus derived was then verified via theoretical analysis under different scenarios,full-scale model testing,and field testing and commissioning.Findings–Two major types of BEJs,deck-type and through-type,are used in HSR long-span bridges in China.Typical BEJ faults were found to mainly include skewness of steel sleepers at the bridge gap,abnormally large longitudinal frictional resistance,and flexural deformation of the scissor mechanisms.These faults influence BEJ functioning,and thus adversely affect track quality and train running performance at the beam end.Due to their simple and integral structure,deck-type BEJs with expansion range 1200 mm(±600 mm)or less have been favored as a solution offering improved operational conditions,and have emerged as a standard design.However,when the expansion range exceeds the above-mentioned value,special design work becomes necessary.Therefore,based on engineering practice,a performance-based integral design method for BEJs used with REJs was proposed,taking into account four major categories of performance requirements,i.e.,mechanical characteristics,train running quality,durability and insulation performance.Overall BEJ design must mainly consider component strength and the overall stiffness of BEJ;the latter factor in particular has a decisive influence on train running performance at the beam end.Detailed BEJ structural design must stress minimization of the frictional resistance of its sliding surface.The static and dynamic performance of the newlydesigned BEJ with expansion range 1600 mm have been confirmed to be satisfactory,via numerical simulation,full-scale model testing,and field testing and commissioning.Originality/value–This research provides a broad overview of the status of BEJs with large expansion range in HSR long-span bridges in China,along with novel insights into their design.展开更多
High-finesse optical reference cavities are essential tools for fundamental research.In response to China’s historical reliance on importing high-finesse optical reference cavities,we successfully developed a cavity ...High-finesse optical reference cavities are essential tools for fundamental research.In response to China’s historical reliance on importing high-finesse optical reference cavities,we successfully developed a cavity using ultralow expansion glass(ULE)materials and processed it entirely in China.Using the method of measuring the cavity linewidth,a finesse of approximately 480000 was obtained in our experiments.We adopted a relatively simple and effective approach to test the optical reference cavity,which involved measuring the resonant points using an ultrastable laser.Remarkably,an expansion coefficient of the Chinese ULE optical reference cavity reached up to the order of 10^(-9)/K within the temperature range of 27℃to 40℃,with the zero expansion point occurring at approximately 34oC.These findings demonstrate China’s independent capability to develop high-finesse optical reference cavities,which is a significant advancement in precision optics.展开更多
Obtaining high-quality 10000-meter-deep seafloor sediment samples is the prerequisite and foundation for conducting deep-sea geological and environmental scientific research.The bottom structure of the deep seafloor i...Obtaining high-quality 10000-meter-deep seafloor sediment samples is the prerequisite and foundation for conducting deep-sea geological and environmental scientific research.The bottom structure of the deep seafloor is complex,and the physical and mechanical properties and disturbance resistance of sediments of different lithologies vary greatly,so the sediment sampler inevitably disturbs the sediments during the sampling process and affects the quality of the sediment samples.A new type of deep-sea sediment pressure retaining sampler is introduced,the force state and elastic–plastic state of the sampler destroying sediments are analyzed,the radial disturbance model of sediment coring based on the spherical cavity expansion theory is established,and the radius of sediments undergoing plastic deformation around the spherical holes is used as an index for evaluating the radial disturbance of sediments.The distribution of stress and strain fields in the sediments during the expansion of the spherical cavity and the influencing factors of the radius of the radially disturbed region(plastic region)are analyzed using an arithmetic example,and the influence law is analyzed.A sediment disturbance experimental platform was built indoors to simulate the sediment coring process.The radial stress field and pore water pressure of the sediment during the coring process were monitored by sensors arranged inside the sediment,and the results of indoor tests verified the correctness of the perturbation theory model.The sampler was carried aboard the deep-sea manned submersible FENDOUZHE and conducted on-site tests at depths of 9298.4 and 9142.8 m in the Kuril-Kamchatka Trench.Pressure-preserved sediment samples were retrieved,with preservation rates of 94.21%and 92.02%,respectively,which are much higher than the current technical indicator of 80%of pressure-holding ratio for deep-sea sediments.The retrieved sediments have obvious stratification characteristics and little disturbance.展开更多
Global population growth and rising standards of living are the driving factors for the cropland expansion to meet increasing demands.However,there is no clear assessment of the specific losses on ecosystem services c...Global population growth and rising standards of living are the driving factors for the cropland expansion to meet increasing demands.However,there is no clear assessment of the specific losses on ecosystem services caused by China's expansion of cropland to ensure food security at the cost of losing ecological land such as forests and grasslands.This study employed the ArcGIS platform and integrated valuation of ecosystem services and tradeoffs(InVEST)model to explore the cropland expansion in China from 2000 to 2020 and its impact on ecosystem services,so as to predict the priority areas of future cropland expansion in different scenarios.The results indicated that in the past 20 years,the total area of cropland expansion in China was 17.04 million hm^(2)with 70.79% conversion from forests and grasslands.Cropland expansion has contributed to an overall improvement in the food supply services with the Northern Arid and Semi-Arid Region exhibiting an increase of 18.76×10^(6) tons,while concurrently leading to a decline in habitat quality services.The priority areas for future cropland expansion without ecological loss were found to be 1.42 million hm^(2),which only account for 9.44% of the total reclaimable land.To minimize the loss of ecosystem services,there is a need to adjust the cropland replenishment policies and provide an operational solution for global food security and ecological protection.展开更多
Increasing the hole expansion ratio is significant for developing high formability parts.Hole expansion tests were carried out on low carbon hot-rolled steel containing 0.11%Ti,0.072%Ti–0.03%Nb and 0.097%Ti–0.059%Nb...Increasing the hole expansion ratio is significant for developing high formability parts.Hole expansion tests were carried out on low carbon hot-rolled steel containing 0.11%Ti,0.072%Ti–0.03%Nb and 0.097%Ti–0.059%Nb,respectively.The effects of microstructure,texture,crack propagation behavior and second phase precipitation behavior on hole expansion ratio were investigated.The precipitation behavior of TiC and(Ti,Nb)C in austenite and ferrite in three groups of steel samples was calculated theoretically.The results showed that the hole expansion ratios of 0.11Ti,0.072Ti–0.03Nb and 0.097Ti–0.059Nb test steels were 51.73%,51.17%and 66.24%following simulated coiling at 600℃,respectively.The microstructure was mainly polygonal ferrite with a small amount of pearlite.The grain refinement of 0.097Ti–0.059Nb test steel and the low texture ratio of{110}//ND improved the hole expansion ratio.The low overall hole expansion ratio was due to the microstructure inhomogeneity.The microstructure uniformity was improved by the quenching and tempering treatment,and the hole expansion ratio of the three test steels was greatly increased.The fastest precipitation temperatures in the austenitic region of 0.11Ti,0.072Ti–0.03Nb and 0.097Ti–0.059Nb test steels were 880,860 and 830℃,while those in the ferrite region were 680,675 and 675℃,respectively.The addition of Nb element increased the volume free energy,so that the critical core size of the nucleation on the dislocation line increased,resulting in the decrease in the fastest precipitation temperature.展开更多
基金partially supported by National Funds through FCT-"Fundacao para a Ciencia e a Tecnologia",(PEst-OE/MAT/UI0212/2011)supported by Basic Science Research Program through the National Research Foundation of Korea(NRF)funded by the Ministry,ICT&Future Planning(No.2014R1A1A1A05002124)supported by National Natural Science Foundation of China(No.11301018 and 11371046)
文摘We prove that a Cl-generic volume-preserving dynamical system （diffeomor- phism or flow） has the shadowing property or is expansive or has the weak specification property if and only if it is Anosov. Finally, as in [10, 27], we prove that the Cl-robustness, within the volume-preserving context, of the expansiveness property and the weak specifica- tion property, imply that the dynamical system （diffeomorphism or flow） is Anosov.
基金Wang and Zhu are supported by NSFC (Grant Nos.11771118,11801336,12171400)Wang is also supported by China Postdoctoral Science Foundation (No.2021M691889)。
文摘In this paper,forward expansiveness and entropies of"subsystems"2)of Z^(k)_(+)-actions are investigated.Letαbe a Z^(k)_(+)-action on a compact metric space.For each 1≤j≤k-1,denote G^(j)_(+)={V+:=V∩R^(k)_(+):V is a j-dimensional subspace of R^(k)}.We consider the forward expansiveness and entropies forαalong V+∈G^(j)_(+).Adapting the technique of"coding",which was introduced by M.Boyle and D.Lind to investigate expansive subdynamics of Z^(k)-actions,to the Z^(k)_(+)cases,we show that the set E^(j)_(+)(α)of forward expansive j-dimensional V_(+)is open in G^(j)_(+).The topological entropy and measure-theoretic entropy of j-dimensional subsystems ofαare both continuous in E^(j)_(+)(α),and moreover,a variational principle relating them is obtained.For a 1-dimensional ray L∈G^(+)_(1),we relate the 1-dimensional subsystem ofαalong L to an i.i.d.random transformation.Applying the techniques of random dynamical systems we investigate the entropy theory of 1-dimensional subsystems.In particular,we propose the notion of preimage entropy(including topological and measure-theoretical versions)via the preimage structure ofαalong L.We show that the preimage entropy coincides with the classical entropy along any L∈E1+(α)for topological and measure-theoretical versions respectively.Meanwhile,a formula relating the measure-theoretical directional preimage entropy and the folding entropy of the generators is obtained.
基金supported in part by the National Key Research and Development Program of China (Grant No.2020YFC2201504)the National Natural Science Foundation of China (Grant Nos.12588101 and 12535002)。
文摘We investigate the null tests of cosmic accelerated expansion by using the baryon acoustic oscillation(BAO)data measured by the dark energy spectroscopic instrument(DESI)and reconstruct the dimensionless Hubble parameter E(z)from the DESI BAO Alcock-Paczynski(AP)data using Gaussian process to perform the null test.We find strong evidence of accelerated expansion from the DESI BAO AP data.By reconstructing the deceleration parameter q(z) from the DESI BAO AP data,we find that accelerated expansion persisted until z■0.7 with a 99.7%confidence level.Additionally,to provide insights into the Hubble tension problem,we propose combining the reconstructed E(z) with D_(H)/r_(d) data to derive a model-independent result r_(d)h=99.8±3.1 Mpc.This result is consistent with measurements from cosmic microwave background(CMB)anisotropies using the ΛCDM model.We also propose a model-independent method for reconstructing the comoving angular diameter distance D_(M)(z) from the distance modulus μ,using SNe Ia data and combining this result with DESI BAO data of D_(M)/r_(d) to constrain the value of r_(d).We find that the value of r_(d),derived from this model-independent method,is smaller than that obtained from CMB measurements,with a significant discrepancy of at least 4.17σ.All the conclusions drawn in this paper are independent of cosmological models and gravitational theories.
文摘China’s booming performing arts sector is reshaping cultural experiences and creating vibrant new spaces for leisure,tourism and creativity The year 2025 marked a period of vigorous expansion for China’s performing arts sector,as the industry evolved from a traditional entertainment field into a comprehensive engine of cultural consumption.
基金financially supported by National Natural Science Foundation of China(No.52175321)the Fund of Key Laboratory of High Temperature Electromagnetic Materials and Structure of MOE(No.KB202505)。
文摘There is an urgent need to develop magnesium-matrix materials that exhibit both high thermal conductivity and low thermal expansion to ensure compatibility with chips.This study aims to develop a Mg-Zn-Cu alloy with high thermal conductivity.Furthermore,it explores the preparation of AlN_(P)/Mg-Zn-Cu composites featuring low coefficients of thermal expansion.The stir casting method was utilized to fabricate the composites and an investigation was conducted to examine their microstructure and thermal properties.Results indicate that the addition of AlN_(P)reduces the thermal expansion coefficient while maintaining relatively high thermal conductivity.Specifically,the AlN_(P)/Mg-0.5Zn-0.5Cu composite with 30wt.%AlN_(P)achieves a thermal conductivity of 132.7 W·m^(-1)·K^(-1)and a thermal expansion coefficient of 18.5×10^(-6)K^(-1),rendering it suitable for electronic packaging applications where thermal management is critical.
基金funded by the Russian Science Foundation(RSF),grant No.25-73-20038(conceptualization,methodology,manuscript writing).
文摘Due to their chiral structure,carbon nanosprings possess unique properties that are promising for nanotechnology applications.The structural transformations of carbon nanosprings in the form of spiral macromolecules derived from planar coronene and kekulene molecules(graphene helicoids and spiral nanoribbons)are analyzed using molecular dynamics simulations.The interatomic interactions are described by a force field including valence bonds,bond angles,torsional and dihedral angles,as well as van derWaals interactions.While the tension/compression of such nanosprings has been analyzed in the literature,this study investigates other modes of deformation,including bending and twisting.Depending on the geometric characteristics of the carbon nanosprings,the formation of structural and helix reversal topological defects is described.During these structural transformations of the nanosprings,only van der Waals bonds break and recover,but breaking or recovery of covalent bonds does not take place.It is found that nanosprings demonstrate a significantly higher coefficient of axial thermal expansion than many metals and alloys.Under axial compression,Euler instability leads to lateral bending with continuous deformation of the nanospring axis at relatively low compression,while at high compression,bending kinks form.Various types of topological defects form on the instantly released nanospring during its relaxation from a highly stretched configuration.These results are useful for the development of nanosensors operating over a wide temperature range.
基金supported by the SERB,SUR/2022/002244,Govt.India and the second author was supported by the UGC-JRF(NTA Ref.No.:201610135853)New Delhi,India,and the third author was partially supported by the JSPS KAKENHI(JP22K03363).
文摘In this paper,we first establish refined versions of the Bohr inequalities for the class of holomorphic functions from the unit ball BX of a complex Banach space X into ℂ.As applications,we will establish refined Bohr inequalities of functional type or of norm type for holomorphic mappings with lacunary series on the unit ball BX with values in higher dimensional spaces.Next,we obtain the Bohr-Rogosinski inequality for the class of holomorphic functions on BX.In addition,we establish an improved version of the Bohr inequality for holomorphic functions on BX.All the results are proved to be sharp.
基金supported by the operating fund of Key Laboratory of Nuclear Power Systems and Equipment(Shanghai Jiao Tong University),Ministry of Education,China,the Natural Science Foundation of Shanghai Municipality(25ZR1402177)the National Natural Science Foundation of China(12105167)。
文摘Fuel-coolant interaction(FCI)remains one of the most complex challenges in severe accident research,with the triggering process being a key aspect that may govern subsequent fine fragmentation and potential steam explosions.In this study,the evolution characteristics of droplet-water interactions under external disturbance conditions were investigated using a self-designed FCI experimental setup.The experimental observations revealed that cavity formation reduced the drag force on the droplet,thereby increasing its peak velocity.However,the external disturbance pressure can disrupt the cavity,leading to a reduction in the droplet peak velocity.Furthermore,it was found that an increase in external disturbance pressure tended to increase the peak value of the droplet expansion rate,thereby promoting the fine-fragmentation process.This effect holds regardless of the initial droplet temperature,coolant temperature,or even when using droplet materials such as lead,which is generally considered unfavorable for steam explosions.Comparative analyses indicated that a higher external disturbance pressure may shorten the triggering time of the droplet surface and enhance the trigger intensity.These findings provide important phenomenological insights for further investigation of the triggering mechanisms in the initial stage of fuel-coolant interactions.
基金National Key Research and Development Program of China,No.2019YFD1101304National Natural Science Foundation of China,No.52278059+1 种基金Natural Science Foundation of Hunan Province of China,No.2024JJ8316Hunan Provincial Innovation Foundation For Postgraduate,No.CX20250634。
文摘Urban spatial morphology(USM)optimization is critical to balancing biodiversity conservation and sustainable urbanization.However,previous studies predominantly focused on the socio-economic efficiency and static ecological metrics and rarely addressed the dynamic USM optimization across spatial scales.Here,we developed a multi-level ecological network(MEN)framework to resolve the tension between urban expansion and ecological integrity.By integrating the cost-weighted distance analysis with a hierarchical network transmission mechanism,we established a cross-scale spatial optimization system,which coordinated the regional ecological corridors and local habitat patches.Comparative experiments with conventional single-scale approaches and scenario simulations using the PLUS model show that the MEN framework had superior performance in three dimensions:(1)spatial governance:the primary-level network(peri-urban natural reserves)effectively contained urban sprawl,and the secondary-level network(intra-urban green corridors)mitigated habitat fragmentation and improved the built-environment;(2)scenario robustness:the model maintained an optimal compactness-loose balance in multiple development pathways;(3)landscape metrics:patch fragmentation decreased by 18.25%,and the internal landscape richness improved by 10.66%compared to the scenario without USM optimization.The findings provide new insight to establish a hierarchical ecological optimization framework as a nature-based spatial protocol to reconcile metropolitan growth with landscape sustainability.
基金funded by the National Key R&D Program of China,China(No.2024YFF0507903)the National Key Research and Development Program of China(Grant No.2024YFF0507904)the National Natural Science Foundation of China,China(Grant No.52379114).These supports are gratefully acknowledged.
文摘In-situ enlargement of super-large-span tunnels can intensify excavation-induced unloading in the surrounding rock,increasing deformation demand and failure risk during construction.This study combines laboratory model tests with FLAC3D simulations to evaluate the stabilizing role of prestressed anchor cables and to establish an energy-balance framework for support optimization.Comparative model tests of existing and enlarged tunnel sections,with and without anchors,show that reinforcement increases load-carrying capacity,reduces displacement,and confines damage to more localized zones.The numerical simulations reproduce displacement fields,shear-strain localization,and plastic-zone evolution with good agreement against the experimental observations.The energy framework is implemented in the in-situ simulations by quantifying unloading-related energy release in the rock mass and reinforcement work contributed by the anchors,and by introducing an energy release–reinforcement ratio as a stability indicator.Parametric analyses indicate that anchor length,spacing,and prestress influence stability in a nonlinear manner,with diminishing returns once reinforcement extends beyond the mechanically dominant deformation zone.An efficient parameter window is identified that improves deformation and yielding control while avoiding unnecessary reinforcement.The results provide an energy-consistent and design-oriented basis for prestressed anchorage selection in large-span tunnel expansion.
基金supported by the doctoral scholarship of the author, André Alves, funded by the Foundation for Science and Technology (FCT) through the MIT Portugal Programme (PRT/BD/154418/2023)the State Budgetprovided through FCT funding, was received from the MOPT Research Group of the Centre of Geographical Studies, University of Lisbon (UID/295/2025, DOI: 10.54499/UID/00295/2025), and from the Centro de Investigação em Gestão de Informação (MagIC) under the projects UID/04152/2025 (DOI: 10.54499/UID/04152/2025,2025–01–01 to 2028–12–31) and UID/PRR/04152/2025 (DOI: 10.54499/UID/PRR/04152/2025,2025–01–01 to 2026–06–30)
文摘The growing demand for land to accommodate renewable energy infrastructure has intensified competition with biodiversity conservation, agriculture, and ecosystem services. In Portugal, electricity system decarbonisation relies heavily on utility-scale solar energy(USSE) facilities, yet the spatial extent of land transformation associated with photovoltaic development has not been systematically assessed. This study provides an assessment of the land occupancy of USSE facilities and associated land use and land cover(LULC) changes in continental Portugal over the past two decades, as well as their spatial relationship with areas designated for land and nature conservation. A geospatial database of USSE installations(≥1 MW) was developed through the integration of multiple data sources using geographic information systems(GIS). The geometric consistency of spatial features was ensured through harmonisation and validation procedures involving GIS-based corrections supported by Sentinel-2 satellite imagery. Spatial overlay analyses were conducted with multitemporal LULC datasets and with land-use planning constraints, including areas classified for nature conservation, ecological reserves, and agricultural reserves. The results indicate that USSE deployment has been predominantly located in the southern regions of Portugal, although the location of planned projects indicates a northward shift. The implementation of USSE facilities has been mainly associated with LULC changes in forest land, agricultural areas, pastures and shrubland. Spatial overlaps were observed with areas classified within the national ecological and agricultural reserves.These patterns may be indicative of growing land-use conflicts, but the extent to which these developments align with land-use planning objectives and conservation priorities requires further examination.
基金Supported by the Key R&D Program of Shandong Province(No.2023CXGC010411)the National Key R&D Program of China(Nos.2023YFD2400800,2022YFD2401301,2022FY100304)+2 种基金the National Natural Science Foundation of China(Nos.42076092,41906083,41776179)the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDB42000000)the Earmarked Fund for Modern Agro-industry Technology Research System(No.CARS-47)。
文摘The Saccostrea mordax Gould,1850 is a typical intertidal species,whose genetic differentiation is influenced by various factors,including geological and climatic changes.To explore the genetic structure and historical population characteristics of Saccostrea mordax,we sequenced the mitochondrial cytochrome c oxidase subunit I(COI)gene from 58 specimens sampled from four locations in the western Pacific.Additionally,103 individuals from the Persian Gulf and western Pacific(from databases)were included for phylogenetic analysis.The Bayesian Inference tree showed that all specimens were divided into two clades,i.e.,the Persian Gulf population and the western Pacific population.Spatial molecular variance analysis indicated significant genetic differentiation between the two populations,and isolation by distance analysis revealed a positive correlation between genetic differentiation and geographic distance.Neutrality tests and Bayesian Skyline Plot suggested that both populations underwent expansions during the late Pleistocene.This study revealed the population history of Saccostrea mordax and described a new lineage,Saccostrea mordax lineage D,providing a foundation for understanding oyster biodiversity formation and genetic resource conservation.
基金financial support from the National Natural Science Foundation of China(No.22478278,22308246)the Central Government Guides the Local Science and Technology Development Special Fund(No.YDZJSX20231A015)the Fundamental Research Program of Shanxi Province(No.202203021212266).
文摘The metallic Ni catalyst suffers from strong binding with the*CO intermediate,resulting in poisoning of the catalyst surface.It is feasible to facilitate the generation of CO by alleviating the binding strength of the*CO intermediate on the Ni metal surface through a lattice expansion strategy.Here,Ni_(3)ZnC_(0.7)@C with lattice expansion was synthesized by co-doping with Zn and interstitial C through high-temperature pyrolysis.Structural characterization confirms that the lattice of Ni_(3)ZnC_(0.7)expands by 5.47%compared to Ni due to the co-doping of Zn and interstitial C.The Ni_(3)ZnC_(0.7)@C possesses excellent catalytic performance with Faradaic efficiency(FE)of CO exceeding 90%over a wide potential range from−0.8 to−1.4 V versus reversible hydrogen electrode(vs.RHE)with a peak FECO of 96.6%at−1.0 V vs.RHE.In membrane electrode assembly(MEA)testing,Ni_(3)ZnC_(0.7)@C achieves a FECO of 81.4%at the industrial-level current density of 400 mA cm^(−2).In situ attenuated total reflection surface-enhanced infrared absorption spectroscopy(ATR-SEIRAS)and density functional theory(DFT)calculations reveal that the co-introduction of Zn and interstitial C in the Ni crystal can significantly promote the desorption of*CO intermediate,which facilitates the generation of CO.This study demonstrates a viable way for designing efficient transition metal catalysts for CO_(2)electroreduction through lattice strain engineering.
基金funded by the National Natural Science Foundation of China(Grant No.42377331)supported by the U.S.National Science Foundation Division of Environmental Biology award#2331162U.S.National Science Foundation Dynamics of Integrated Socio-Environmental Systems award#2408954.
文摘Large-scale afforestation and forest conservation policies have been widely implemented in Southwest China over past decades.These efforts have significantly protected the remaining long-established forests in the region and greatly expanded forested areas.Utilizing nearly 30 years of satellite time-series data,we reveal that the region’s enhanced carbon sequestration(3×10^(12) g·C annually)is primarily driven by crucial changes in forest structure and age,occurring alongside a nearly 120%increase in forested land area.We observe that dense forests maintain a rapid growth rate of approximately 2.5%annually for carbon sequestration in the initial years after establishment.However,this growth rate decelerates with increasing apparent forest age.Meanwhile,the densification(modeled as an increasing forest probability)rate of forests reaches its peak growth during the 10-20 year period,sustaining a high annual growth rate of about 1.8%.We also find that improvements in forest structure,particularly the increasing of forest canopy density and apparent forest age coupled with a notable reduction in forest fragmentation,are also the main driving factors for the enhanced carbon sequestration capacity.Based on these findings,we conclude that forest restoration policies in Southwest China have been successful not only in facilitating large-scale forest growth in Southwest China but,more critically,in promoting the structural maturation(e.g.,densification and reduced fragmentation)that is essential for enhancing the region’s carbon sink capacity and its resilience.
基金National Key R&D Program of China(2022YFB2602900)R&D Fund Project of China Academy of Railway Sciences Corporation Limited(2021YJ084)+2 种基金Project of Science and Technology R&D Program of China Railway(2016G002-K)R&D Fund Project of China Railway Major Bridge Reconnaissance&Design Institute Co.,Ltd.(2021)R&D Fund Project of China Railway Shanghai Group(2021141).
文摘Purpose–The bridge expansion joint(BEJ)is a key device for accommodating spatial displacement at the beam end,and for providing vertical support for running trains passing over the gap between the main bridge and the approach bridge.For long-span railway bridges,it must also be coordinated with rail expansion joint(REJ),which is necessary to accommodate the expansion and contraction of,and reducing longitudinal stress in,the rails.The main aim of this study is to present analysis of recent developments in the research and application of BEJs in high-speed railway(HSR)long-span bridges in China,and to propose a performance-based integral design method for BEJs used with REJs,from both theoretical and engineering perspectives.Design/methodology/approach–The study first presents a summary on the application and maintenance of BEJs in HSR long-span bridges in China representing an overview of their state of development.Results of a survey of typical BEJ faults were analyzed,and field testing was conducted on a railway cable-stayed bridge in order to obtain information on the major mechanical characteristics of its BEJ under train load.Based on the above,a performance-based integral design method for BEJs with maximum expansion range 1600 mm(±800 mm),was proposed,covering all stages from overall conceptual design to consideration of detailed structural design issues.The performance of the novel BEJ design thus derived was then verified via theoretical analysis under different scenarios,full-scale model testing,and field testing and commissioning.Findings–Two major types of BEJs,deck-type and through-type,are used in HSR long-span bridges in China.Typical BEJ faults were found to mainly include skewness of steel sleepers at the bridge gap,abnormally large longitudinal frictional resistance,and flexural deformation of the scissor mechanisms.These faults influence BEJ functioning,and thus adversely affect track quality and train running performance at the beam end.Due to their simple and integral structure,deck-type BEJs with expansion range 1200 mm(±600 mm)or less have been favored as a solution offering improved operational conditions,and have emerged as a standard design.However,when the expansion range exceeds the above-mentioned value,special design work becomes necessary.Therefore,based on engineering practice,a performance-based integral design method for BEJs used with REJs was proposed,taking into account four major categories of performance requirements,i.e.,mechanical characteristics,train running quality,durability and insulation performance.Overall BEJ design must mainly consider component strength and the overall stiffness of BEJ;the latter factor in particular has a decisive influence on train running performance at the beam end.Detailed BEJ structural design must stress minimization of the frictional resistance of its sliding surface.The static and dynamic performance of the newlydesigned BEJ with expansion range 1600 mm have been confirmed to be satisfactory,via numerical simulation,full-scale model testing,and field testing and commissioning.Originality/value–This research provides a broad overview of the status of BEJs with large expansion range in HSR long-span bridges in China,along with novel insights into their design.
基金supported by the National Natural Science Foundation of China(Grant Nos.12103059 and 12033007)the National Major Science and Technology Infrastructure Project of China(Grant No.2017-000052-73-01-002401)+3 种基金Xi’an Science and Technology Bureau(Grant No.E019XK1S04)Sanqin Talents’Special Support Program(Grant No.09R0557A00)the Youth Innovation Promotion Association of the Chinese Academy of Science(Grant No.1188000XGJ)the Innovation Program for Quantum Science and Technology(Grant No.2021ZD0300900)。
文摘High-finesse optical reference cavities are essential tools for fundamental research.In response to China’s historical reliance on importing high-finesse optical reference cavities,we successfully developed a cavity using ultralow expansion glass(ULE)materials and processed it entirely in China.Using the method of measuring the cavity linewidth,a finesse of approximately 480000 was obtained in our experiments.We adopted a relatively simple and effective approach to test the optical reference cavity,which involved measuring the resonant points using an ultrastable laser.Remarkably,an expansion coefficient of the Chinese ULE optical reference cavity reached up to the order of 10^(-9)/K within the temperature range of 27℃to 40℃,with the zero expansion point occurring at approximately 34oC.These findings demonstrate China’s independent capability to develop high-finesse optical reference cavities,which is a significant advancement in precision optics.
基金supported by the National Key Research and Development Program of China(Nos.2023YFC2809304 and 2022YFC2805904).
文摘Obtaining high-quality 10000-meter-deep seafloor sediment samples is the prerequisite and foundation for conducting deep-sea geological and environmental scientific research.The bottom structure of the deep seafloor is complex,and the physical and mechanical properties and disturbance resistance of sediments of different lithologies vary greatly,so the sediment sampler inevitably disturbs the sediments during the sampling process and affects the quality of the sediment samples.A new type of deep-sea sediment pressure retaining sampler is introduced,the force state and elastic–plastic state of the sampler destroying sediments are analyzed,the radial disturbance model of sediment coring based on the spherical cavity expansion theory is established,and the radius of sediments undergoing plastic deformation around the spherical holes is used as an index for evaluating the radial disturbance of sediments.The distribution of stress and strain fields in the sediments during the expansion of the spherical cavity and the influencing factors of the radius of the radially disturbed region(plastic region)are analyzed using an arithmetic example,and the influence law is analyzed.A sediment disturbance experimental platform was built indoors to simulate the sediment coring process.The radial stress field and pore water pressure of the sediment during the coring process were monitored by sensors arranged inside the sediment,and the results of indoor tests verified the correctness of the perturbation theory model.The sampler was carried aboard the deep-sea manned submersible FENDOUZHE and conducted on-site tests at depths of 9298.4 and 9142.8 m in the Kuril-Kamchatka Trench.Pressure-preserved sediment samples were retrieved,with preservation rates of 94.21%and 92.02%,respectively,which are much higher than the current technical indicator of 80%of pressure-holding ratio for deep-sea sediments.The retrieved sediments have obvious stratification characteristics and little disturbance.
基金supported by the National Natural Science Foundation of China(Grant No.52374170)the Major Special Projects of the Third Comprehensive Scientific Exploration in Xinjiang(Grant No.2022xjkk1005)the Fundamental Research Funds for the Central Universities(Grant No.B230207001)。
文摘Global population growth and rising standards of living are the driving factors for the cropland expansion to meet increasing demands.However,there is no clear assessment of the specific losses on ecosystem services caused by China's expansion of cropland to ensure food security at the cost of losing ecological land such as forests and grasslands.This study employed the ArcGIS platform and integrated valuation of ecosystem services and tradeoffs(InVEST)model to explore the cropland expansion in China from 2000 to 2020 and its impact on ecosystem services,so as to predict the priority areas of future cropland expansion in different scenarios.The results indicated that in the past 20 years,the total area of cropland expansion in China was 17.04 million hm^(2)with 70.79% conversion from forests and grasslands.Cropland expansion has contributed to an overall improvement in the food supply services with the Northern Arid and Semi-Arid Region exhibiting an increase of 18.76×10^(6) tons,while concurrently leading to a decline in habitat quality services.The priority areas for future cropland expansion without ecological loss were found to be 1.42 million hm^(2),which only account for 9.44% of the total reclaimable land.To minimize the loss of ecosystem services,there is a need to adjust the cropland replenishment policies and provide an operational solution for global food security and ecological protection.
基金financially supported by the CITIC niobium steel development award Fund(M1656-2021)Central Iron and Steel Research Institute for its independent research and development fund(No.21G62460ZD).
文摘Increasing the hole expansion ratio is significant for developing high formability parts.Hole expansion tests were carried out on low carbon hot-rolled steel containing 0.11%Ti,0.072%Ti–0.03%Nb and 0.097%Ti–0.059%Nb,respectively.The effects of microstructure,texture,crack propagation behavior and second phase precipitation behavior on hole expansion ratio were investigated.The precipitation behavior of TiC and(Ti,Nb)C in austenite and ferrite in three groups of steel samples was calculated theoretically.The results showed that the hole expansion ratios of 0.11Ti,0.072Ti–0.03Nb and 0.097Ti–0.059Nb test steels were 51.73%,51.17%and 66.24%following simulated coiling at 600℃,respectively.The microstructure was mainly polygonal ferrite with a small amount of pearlite.The grain refinement of 0.097Ti–0.059Nb test steel and the low texture ratio of{110}//ND improved the hole expansion ratio.The low overall hole expansion ratio was due to the microstructure inhomogeneity.The microstructure uniformity was improved by the quenching and tempering treatment,and the hole expansion ratio of the three test steels was greatly increased.The fastest precipitation temperatures in the austenitic region of 0.11Ti,0.072Ti–0.03Nb and 0.097Ti–0.059Nb test steels were 880,860 and 830℃,while those in the ferrite region were 680,675 and 675℃,respectively.The addition of Nb element increased the volume free energy,so that the critical core size of the nucleation on the dislocation line increased,resulting in the decrease in the fastest precipitation temperature.
