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
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
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
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
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
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
Due to batteries inconsistencies and potential faults in battery management systems,slight overcharging remains a common yet insufficiently understood safety risk,lacking effective warning methods.To illuminate the de...Due to batteries inconsistencies and potential faults in battery management systems,slight overcharging remains a common yet insufficiently understood safety risk,lacking effective warning methods.To illuminate the degradation behavior and failure mechanism of various overcharged states(100%SOC,105%SOC,110%SOC,and 115%SOC),multiple advanced in-situ characterization techniques(accelerating rate calorimeter,electrochemical impedance spectroscopy,ultrasonic scanning,and expansion instrument)were utilized.Additionally,re-overcharge-induced thermal runaway(TR)tests were conducted,with a specific emphasis on the evolution of the expansion force signal.Results indicated significant degradation at 110%SOC including conductivity loss,loss of lithium inventory,and loss of active material accompanied by internal gas generation.These failure behaviors slow down the expansion force rate during reovercharging,reducing the efficacy of active warnings that depend on rate thresholds of expansion force.Specifically,the warning time for 115%SOC battery is only 144 s,which is 740 s shorter than that for fresh battery,and the time to TR is advanced by 9 min.Moreover,the initial self-heating temperature(T1)is reduced by 62.4℃compared to that of fresh battery,reaching only 70.8℃.To address the low safety of overcharged batteries,a passive overcharge warning method utilizing relaxation expansion force was proposed,based on the continued gas generation after stopping charging,leading to a sustained increase in force.Compared to active methods that rely on thresholds of expansion force rate,the passive method can issue warnings 115 s earlier.By combining the passive and active warning methods,guaranteed effective overcharge warning can be issued 863-884 s before TR.This study introduces a novel perspective for enhancing the safety of batteries.展开更多
Sulfate attack-induced expansion of cement-treated aggregates in seasonally frozen regions is a well-known issue which causes continuous expansion in railway subgrades,and particularly in high-speed railways.According...Sulfate attack-induced expansion of cement-treated aggregates in seasonally frozen regions is a well-known issue which causes continuous expansion in railway subgrades,and particularly in high-speed railways.Accordingly,we investigated the influence of material proportions,the number of freeze-thaw(FT)cycles,and temperature gradients on the expansion mechanism of sulfate attack on cement-treated aggregates subjected to FT cycles.The conditions,laws,and dominant factors causing the expansion of aggregates were analyzed through swelling tests.The results indicate that under FT cycles,3%content cement-treated graded macadam only experiences slight deformation.The maximum strain of graded macadam attacked by 1%sodium sulfate content in each FT cycle is significantly larger than that of 3%content cement-treated graded macadam attacked by 1%sodium sulfate content.Using scanning electron microscopy,needle-like crystals were observed during sulfate attack of cement-treated graded macadam.Through quantitative analysis,we determined the recoverable and unrecoverable deformations of graded macadam under FT cycles.For graded macadam under sulfate attack,the expansion is mainly induced by periodic frost heave and salt expansion,as well as salt migration.For cement-treated graded macadam under sulfate attack,the expansion is mainly induced by chemical attack and salt migration.This study can serve as a reference for future research on the mechanics of sulfate attack on cement-treated aggregates that experience FT cycles,and provide theoretical support for methods that remediate the expansion induced by sulfate attack.展开更多
Negative thermal expansion(NTE)is a notable physical property where a material’s volume decreases instead of increasing when heated.The identification of NTE materials is crucial for thermal expansion control enginee...Negative thermal expansion(NTE)is a notable physical property where a material’s volume decreases instead of increasing when heated.The identification of NTE materials is crucial for thermal expansion control engineering.Most NTE materials exhibit NTE only within a narrow temperature range,restricting their applications.Achieving NTE across a broad temperature range remains a significant challenge.This study developed a novel PbTiO_(3)-based system,(1-x)PbTiO_(3–x)BiLuO_(3),incorporating rare-earth elements,using a distinctive high-pressure and high-temperature synthesis technique.We achieved NTE across a broad temperature range by coupling lattice(c/a)with ferroelectric order parameters.The incorporation of BiLuO_(3)resulted in distinctive ferroelectric characteristics,including increased tetragonality,spontaneous polarization,and NTE over a broad temperature range.NTE over an extended temperature range has been achieved in 0.95PbTiO_(3)–0.05BiLuO_(3)(■=−1.7×10^(–5)K^(−1),300–840 K)and 0.90PbTiO_(3)–0.10BiLuO_(3)(■=−1.4×10^(–5)K^(−1),300–860 K),compared to pristine PbTiO_(3)(■=−1.99×10^(–5)K^(−1),300–763 K).The improved tetragonalities and broader NTE temperature range result from the strong hybridization of Pb/Bi–O and Ti/Lu–O atoms,as demonstrated by combined experimental and theoretical analyses,including high-energy synchrotron X-ray diffraction,Raman spectroscopy,and density functional theory calculations.This study introduces a novel example of NTE over a broad temperature range,highlighting its potential as a high-performance thermal expansion compensator.Additionally,it presents an effective method for incorporating rare-earth elements to achieve NTE in PbTiO_(3)-based perovskites across a wide temperature range.展开更多
Minimizing the thermal expansion coefficient(TEC)mismatch between the cathode and electrolyte in solid oxide fuel cells is crucial for achieving stable,durable operation and high performance.Recently,materials with ne...Minimizing the thermal expansion coefficient(TEC)mismatch between the cathode and electrolyte in solid oxide fuel cells is crucial for achieving stable,durable operation and high performance.Recently,materials with negative thermal expansion(NTE)have at-tracted significant attention as effective additives for tailoring the thermomechanical properties of electrodes and enhancing cell durability.In this work,for the first time,single-phase NTE perovskite Sm_(0.85)Zn_(0.15)MnO_(3−δ)(SZM15)was successfully synthesized via the sol-gel method,eliminating the unwanted ZnO phase typically observed in materials obtained through the conventional solid-state reaction route.The sol-gel approach proved highly advantageous,offering low cost,robustness,excellent chemical homogeneity,precise compositional control,and high phase purity.After optimization of synthesis parameters,a negative TEC of approximately−6.5×10^(−6)K^(−1)was achieved in the 400-850℃range.SZM15 was then incorporated as an additive(10wt%-50wt%)into a SmBa0.5Sr0.5CoCuO_(5+δ)(SBSCCO)cathode to tune the thermomechanical properties with a La_(0.8)Sr_(0.2)Ga_(0.8)Mg_(0.2)O_(3−δ)(LSGM)electrolyte,achieving a minimal TEC mismatch of only 1%.Notably,the SBSCCO+10wt%SZM15 composite cathode exhibited the lowest polarization resistance of 0.019Ω·cm^(2)at 900℃,showing approximately 70%lower than that of the pristine cathode.Excellent long-term stability after 100 h of operation was achieved.In addition,a high peak power density of 680 mW·cm^(−2)was achieved in a Ni-YSZ(yttria-stabilized zirconia)|YSZ|Ce_(0.9)Gd_(0.1)O_(2−δ)(GDC10)|SBSCCO+10wt%SZM15 anode-supported fuel cell at 850℃,highlighting the effectiveness of incorporating NTE materials as a promising strategy for regulating the thermomechanical properties and improving the long-term stability of intermediate temperature solid oxide fuel cells(IT-SOFCs).展开更多
Introduction The predominant characteristics of high-altitude climates include low air pressure,low humidity,and large diurnal temperature fluctuations.In practical engineering scenarios in high-altitude regions,many ...Introduction The predominant characteristics of high-altitude climates include low air pressure,low humidity,and large diurnal temperature fluctuations.In practical engineering scenarios in high-altitude regions,many pier surface cracks only appear several months after erection,and cyclic thermal stress is identified as the main trigger for such cracking.The thermal stress in concrete structures has been investigated for decades but remains incompletely understood.Structural engineers typically regard concrete as an isotropic material and calculate the thermal stress using code-specified coefficients of thermal expansion(CTEs)along with temperature conditions and constraints.Because the CTE of hardened cement paste is more than twice that of many aggregates,reducing the CTE of coarse aggregates can further exacerbate the thermal deformation incompatibility between the coarse aggregate and mortar matrix.In this paper,a comprehensive thermal-elastic mechanics model for pier concrete was developed to analysis the temperature-induced surface stress.Methods A series of mechanical and thermophysical tests were conducted on the diorite aggregate,ITZ cement paste,and mortar,and concrete.A test pier was constructed on open ground near the Yarlung Zangbo River at an altitude of 3800 m.The pier had a diameter of 1.8 m and height of 2 m.Temperature sensors were embedded in the cross-section at a height of 1 m,positioned along the southnorth and east-west directions.The embedding depths(distances from the pier surface)were 0,1.5,3,4.5,6,7.5,9,12,15,20,25,30,35,40,50,60,70,80 cm,and 90 cm.A model of the bridge pier concrete for surface-level analysis was constructed.The model consists of a concrete unit formed as a sphere-shell-shell composite,including the aggregate,ITZ,and mortar layers,embedded in the surface layer of a bridge pier.Outside this unit,the pier concrete was treated as an isotropic,homogeneous elastic material.The real-time internal temperature fields of high-altitude concrete bridge piers,measured on-site,were incorporated into the model.By applying thermoelastic mechanics theory and finite element solutions for plane strain problems,the three-dimensional thermal stresses on the surface layer of high-altitude bridge piers were analyzed Results and discussion During the experimental period,the lowest and highest temperatures on the bridge pier in the high-altitude region were 9.6 ℃ and 42.6 ℃,respectively.These occurred before sunrise and sunset on sunny days,respectively,corresponding to the local maximum temperature gradients during the surface heating and cooling stages,as well as the maximum temperature difference between the surface and center during these stages.The thermal stress on the pier concrete surface was obtained by superimposing the stresses caused by the uneven distribution of the internal temperature field and those caused by the incompatible thermal deformation among the different components in the surface concrete Before the erection of the upper structures,the absolute values of the tangential and vertical stresses were the same;therefore,only one curve was observed.From 22:00 to 8:00,the pier concrete surface was in tension,whereas from 11:00 to 22:00,the pier concrete surface was in compression.The surface of the pier concrete was subjected to biaxial forces of equal magnitude with a maximum compressive stress of 12.52 MPa and maximum tensile stress of 2.15 MPa,respectively at 18:00 and 8:00.According to the fatigue equation,the concrete was predicted to crack after 21 d of temperature cycling.Moreover,if humidity-induced stress is added on top of this,the tensile stress may approach or even exceed the concrete's tensile strength,thereby posing a significant risk of cracking.After the erection of upper structures,the tangential and vertical stresses no longer coincide because the upper structures have been erected.The curve of the tangential stress is unchanged,whereas the curve of the vertical stress is translated downwards by 1.57 MPa due to the structural deadweight.Therefore,the maximum tangential compressive stress remained 12.52 MPa,whereas the maximum vertical compressive stress increased to 14.09 MPa.Additionally,the maximum tangential tensile stress was 2.15 MPa,and the maximum vertical tensile stress was 0.58 MPa.According to Appendix C of GB/T 50010 and the fatigue equation,stresses are unlikely to cause cracking of the pier concrete surface.Although a higher CTE of the coarse aggregate slightly increased the maximum compressive stress,the differences among the three groups of concrete were minimal and could be ignored.Specifically,the maximum compressive stresses on the pier concrete surface were 12.54,12.45 MPa,and 12.56 MPa when using diorite,limestone,and basalt,respectively.By contrast,a lower CTE of the coarse aggregate results in a greater maximum tensile stress on the pier concrete surface.For example,when using limestone,which has a low CTE,the maximum tensile stress on the pier concrete surface is 2.28 MPa,compared to 2.17 MPa when using diorite and 2.14 MPa when using basalt.The finite element simulation results indicated that the maximum compressive stress on the pier concrete surface was 11.72 MPa,whereas the maximum tensile stress was 2.10 MPa.These results are approximately consistent with the theoretical calculations.This consistency provides mutual verification.Conclusions Surface cracking in pier concrete occurs predominantly before the erection of upper structures.Under sunny conditions,the orthogonal decomposition of the superficial stress revealed that the maximum compressive stress during the day was approximately 12.52 MPa,whereas the maximum tensile stress was approximately 2.15 MPa.This tensile stress approached the tensile strength of the C35 concrete under biaxial tension.The risk of cracking increased significantly when humidity-induced stress was considered.After the erection of upper structures,the maximum tangential tensile stress on the pier surface remained at 2.15 MPa while the maximum vertical stress decreased to 0.58 MPa,both of which are well below the tensile strength of C35 concrete under biaxial tension.Although the use of coarse aggregates with a lower coefficient of thermal expansion reduced the tensile stress induced by temperature gradients,it increased the stress owing to material deformation incompatibility,leading to a slight increase in the maximum tensile stress on the pier concrete surface.展开更多
This paper investigates ruin,capital injection,and dividends for a two-dimensional risk model.The model posits that surplus levels of insurance companies are governed by a perturbed composite Poisson risk model.This m...This paper investigates ruin,capital injection,and dividends for a two-dimensional risk model.The model posits that surplus levels of insurance companies are governed by a perturbed composite Poisson risk model.This model introduces a dependence between the two surplus levels,present in both the associated perturbations and the claims resulting from common shocks.Critical levels of capital injection and dividends are established for each of the two risks.The surplus levels are observed discretely at fixed intervals,guiding decisions on capital injection,dividends,and ruin at these junctures.This study employs a two-dimensional Fourier cosine series expansion method to approximate the finite time expected discounted operating cost until ruin.The ensuing approximation error is also quantified.The validity and accuracy of the method are corroborated through numerical examples.Furthermore,the research delves into the optimal capital allocation problem.展开更多
For the Sylvester continued fraction expansions of real numbers,FAN et al.(2007)proved that,for almost all real numbers,the nth partial quotient grows exponentially with respect to the product of the first n-1 partial...For the Sylvester continued fraction expansions of real numbers,FAN et al.(2007)proved that,for almost all real numbers,the nth partial quotient grows exponentially with respect to the product of the first n-1 partial quotients.In this paper,we establish the Hausdorff dimension of the exceptional set where the growth rate is a general function.展开更多
As a negative electrode material for lithium-ion batteries,silicon monoxide(SiO)suffers from dramatic volume changes during cycling,causing excessive stress within the electrode and resulting in electrode deformation ...As a negative electrode material for lithium-ion batteries,silicon monoxide(SiO)suffers from dramatic volume changes during cycling,causing excessive stress within the electrode and resulting in electrode deformation and fragmentation.This ultimately leads to a decrease in cell capacity.The trends of volume expansion and capacity change of the SiO/graphite(SiO/C)composite electrode during cycling were investigated via in situ expansion monitoring.First,a series of expansion test schemes were designed,and the linear relationship between negative electrode expansion and cell capacity degradation was quantitatively analyzed.Then,the effects of different initial pressures on the long-term cycling performance of the cell were evaluated.Finally,the mechanism of their effects was analyzed by scanning electron microscope.The results show that after 50 cycles,the cell capacity decreases from 2.556 mAh to 1.689 mAh,with a capacity retention ratio(CRR)of only 66.08%.A linear relationship between the capacity retention ratio and thickness expansion was found.Electrochemical measurements and scanning electron microscope images demonstrate that intense stress inhibits the lithiation of the negative electrode and that the electrode is more susceptible to irreversible damage during cycling.Overall,these results reveal the relationship between the cycling performance of SiO and the internal pressure of the electrode from a macroscopic point of view,which provides some reference for the application of SiO/C composite electrodes in lithium-ion batteries.展开更多
In this paper,we establish common fixed point theorems for expansive map?pings on b-metric-like space and coincidence point for f-weakly isotone increasing mappings in partially ordered b-metric-like space.The main re...In this paper,we establish common fixed point theorems for expansive map?pings on b-metric-like space and coincidence point for f-weakly isotone increasing mappings in partially ordered b-metric-like space.The main results generalize and extend several well-known comparable results from the existing literature.Moreover,some examples are provided to illustrate the main results.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.
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 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.
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(52476200,52106244)the Guangdong Basic and Applied Basic Research Foundation(2024A1515030124)+1 种基金the Science and Technology Project of China Southern Power Grid under Grant GDKJXM20230246(030100KC23020017)the Fundamental Research Funds for the Central Universities。
文摘Due to batteries inconsistencies and potential faults in battery management systems,slight overcharging remains a common yet insufficiently understood safety risk,lacking effective warning methods.To illuminate the degradation behavior and failure mechanism of various overcharged states(100%SOC,105%SOC,110%SOC,and 115%SOC),multiple advanced in-situ characterization techniques(accelerating rate calorimeter,electrochemical impedance spectroscopy,ultrasonic scanning,and expansion instrument)were utilized.Additionally,re-overcharge-induced thermal runaway(TR)tests were conducted,with a specific emphasis on the evolution of the expansion force signal.Results indicated significant degradation at 110%SOC including conductivity loss,loss of lithium inventory,and loss of active material accompanied by internal gas generation.These failure behaviors slow down the expansion force rate during reovercharging,reducing the efficacy of active warnings that depend on rate thresholds of expansion force.Specifically,the warning time for 115%SOC battery is only 144 s,which is 740 s shorter than that for fresh battery,and the time to TR is advanced by 9 min.Moreover,the initial self-heating temperature(T1)is reduced by 62.4℃compared to that of fresh battery,reaching only 70.8℃.To address the low safety of overcharged batteries,a passive overcharge warning method utilizing relaxation expansion force was proposed,based on the continued gas generation after stopping charging,leading to a sustained increase in force.Compared to active methods that rely on thresholds of expansion force rate,the passive method can issue warnings 115 s earlier.By combining the passive and active warning methods,guaranteed effective overcharge warning can be issued 863-884 s before TR.This study introduces a novel perspective for enhancing the safety of batteries.
基金National Natural Science Foundation of China(Nos.42171130 and 42301158)Pilot Project of China’s Strength in Transportation for the Central Research Institute(No.QG2021-1-4-7)National Key Technology Research and Development Program of the Ministry of Science and Technology of China(No.2021YFB2601200).
文摘Sulfate attack-induced expansion of cement-treated aggregates in seasonally frozen regions is a well-known issue which causes continuous expansion in railway subgrades,and particularly in high-speed railways.Accordingly,we investigated the influence of material proportions,the number of freeze-thaw(FT)cycles,and temperature gradients on the expansion mechanism of sulfate attack on cement-treated aggregates subjected to FT cycles.The conditions,laws,and dominant factors causing the expansion of aggregates were analyzed through swelling tests.The results indicate that under FT cycles,3%content cement-treated graded macadam only experiences slight deformation.The maximum strain of graded macadam attacked by 1%sodium sulfate content in each FT cycle is significantly larger than that of 3%content cement-treated graded macadam attacked by 1%sodium sulfate content.Using scanning electron microscopy,needle-like crystals were observed during sulfate attack of cement-treated graded macadam.Through quantitative analysis,we determined the recoverable and unrecoverable deformations of graded macadam under FT cycles.For graded macadam under sulfate attack,the expansion is mainly induced by periodic frost heave and salt expansion,as well as salt migration.For cement-treated graded macadam under sulfate attack,the expansion is mainly induced by chemical attack and salt migration.This study can serve as a reference for future research on the mechanics of sulfate attack on cement-treated aggregates that experience FT cycles,and provide theoretical support for methods that remediate the expansion induced by sulfate attack.
基金financially supported by the National Natural Science Foundation of China(Nos.22271309,12425403 and 12261131499)the National Key R&D Program of China(No.2021YFA1400300)+2 种基金financial support from the Science and Technology Development Fund from Macao SAR(No.0062/2023/ITP2)Macao Polytechnic University(No.RP/FCA-03/2023)Synchrotron X-ray powder diffraction experiments were conducted at SPring-8,approved by the Japan Synchrotron Radiation Research Institute(Nos.2024A1506,2024A1695 and 2024B1807)
文摘Negative thermal expansion(NTE)is a notable physical property where a material’s volume decreases instead of increasing when heated.The identification of NTE materials is crucial for thermal expansion control engineering.Most NTE materials exhibit NTE only within a narrow temperature range,restricting their applications.Achieving NTE across a broad temperature range remains a significant challenge.This study developed a novel PbTiO_(3)-based system,(1-x)PbTiO_(3–x)BiLuO_(3),incorporating rare-earth elements,using a distinctive high-pressure and high-temperature synthesis technique.We achieved NTE across a broad temperature range by coupling lattice(c/a)with ferroelectric order parameters.The incorporation of BiLuO_(3)resulted in distinctive ferroelectric characteristics,including increased tetragonality,spontaneous polarization,and NTE over a broad temperature range.NTE over an extended temperature range has been achieved in 0.95PbTiO_(3)–0.05BiLuO_(3)(■=−1.7×10^(–5)K^(−1),300–840 K)and 0.90PbTiO_(3)–0.10BiLuO_(3)(■=−1.4×10^(–5)K^(−1),300–860 K),compared to pristine PbTiO_(3)(■=−1.99×10^(–5)K^(−1),300–763 K).The improved tetragonalities and broader NTE temperature range result from the strong hybridization of Pb/Bi–O and Ti/Lu–O atoms,as demonstrated by combined experimental and theoretical analyses,including high-energy synchrotron X-ray diffraction,Raman spectroscopy,and density functional theory calculations.This study introduces a novel example of NTE over a broad temperature range,highlighting its potential as a high-performance thermal expansion compensator.Additionally,it presents an effective method for incorporating rare-earth elements to achieve NTE in PbTiO_(3)-based perovskites across a wide temperature range.
基金supported by the research project within the program“Excellence Initiative-Research University”for the AGH University of Krakow(IDUB AGH,Action 21)Kun Zheng acknowledges financial support from AGH University of Krakow(No.16.16.210.476).
文摘Minimizing the thermal expansion coefficient(TEC)mismatch between the cathode and electrolyte in solid oxide fuel cells is crucial for achieving stable,durable operation and high performance.Recently,materials with negative thermal expansion(NTE)have at-tracted significant attention as effective additives for tailoring the thermomechanical properties of electrodes and enhancing cell durability.In this work,for the first time,single-phase NTE perovskite Sm_(0.85)Zn_(0.15)MnO_(3−δ)(SZM15)was successfully synthesized via the sol-gel method,eliminating the unwanted ZnO phase typically observed in materials obtained through the conventional solid-state reaction route.The sol-gel approach proved highly advantageous,offering low cost,robustness,excellent chemical homogeneity,precise compositional control,and high phase purity.After optimization of synthesis parameters,a negative TEC of approximately−6.5×10^(−6)K^(−1)was achieved in the 400-850℃range.SZM15 was then incorporated as an additive(10wt%-50wt%)into a SmBa0.5Sr0.5CoCuO_(5+δ)(SBSCCO)cathode to tune the thermomechanical properties with a La_(0.8)Sr_(0.2)Ga_(0.8)Mg_(0.2)O_(3−δ)(LSGM)electrolyte,achieving a minimal TEC mismatch of only 1%.Notably,the SBSCCO+10wt%SZM15 composite cathode exhibited the lowest polarization resistance of 0.019Ω·cm^(2)at 900℃,showing approximately 70%lower than that of the pristine cathode.Excellent long-term stability after 100 h of operation was achieved.In addition,a high peak power density of 680 mW·cm^(−2)was achieved in a Ni-YSZ(yttria-stabilized zirconia)|YSZ|Ce_(0.9)Gd_(0.1)O_(2−δ)(GDC10)|SBSCCO+10wt%SZM15 anode-supported fuel cell at 850℃,highlighting the effectiveness of incorporating NTE materials as a promising strategy for regulating the thermomechanical properties and improving the long-term stability of intermediate temperature solid oxide fuel cells(IT-SOFCs).
文摘Introduction The predominant characteristics of high-altitude climates include low air pressure,low humidity,and large diurnal temperature fluctuations.In practical engineering scenarios in high-altitude regions,many pier surface cracks only appear several months after erection,and cyclic thermal stress is identified as the main trigger for such cracking.The thermal stress in concrete structures has been investigated for decades but remains incompletely understood.Structural engineers typically regard concrete as an isotropic material and calculate the thermal stress using code-specified coefficients of thermal expansion(CTEs)along with temperature conditions and constraints.Because the CTE of hardened cement paste is more than twice that of many aggregates,reducing the CTE of coarse aggregates can further exacerbate the thermal deformation incompatibility between the coarse aggregate and mortar matrix.In this paper,a comprehensive thermal-elastic mechanics model for pier concrete was developed to analysis the temperature-induced surface stress.Methods A series of mechanical and thermophysical tests were conducted on the diorite aggregate,ITZ cement paste,and mortar,and concrete.A test pier was constructed on open ground near the Yarlung Zangbo River at an altitude of 3800 m.The pier had a diameter of 1.8 m and height of 2 m.Temperature sensors were embedded in the cross-section at a height of 1 m,positioned along the southnorth and east-west directions.The embedding depths(distances from the pier surface)were 0,1.5,3,4.5,6,7.5,9,12,15,20,25,30,35,40,50,60,70,80 cm,and 90 cm.A model of the bridge pier concrete for surface-level analysis was constructed.The model consists of a concrete unit formed as a sphere-shell-shell composite,including the aggregate,ITZ,and mortar layers,embedded in the surface layer of a bridge pier.Outside this unit,the pier concrete was treated as an isotropic,homogeneous elastic material.The real-time internal temperature fields of high-altitude concrete bridge piers,measured on-site,were incorporated into the model.By applying thermoelastic mechanics theory and finite element solutions for plane strain problems,the three-dimensional thermal stresses on the surface layer of high-altitude bridge piers were analyzed Results and discussion During the experimental period,the lowest and highest temperatures on the bridge pier in the high-altitude region were 9.6 ℃ and 42.6 ℃,respectively.These occurred before sunrise and sunset on sunny days,respectively,corresponding to the local maximum temperature gradients during the surface heating and cooling stages,as well as the maximum temperature difference between the surface and center during these stages.The thermal stress on the pier concrete surface was obtained by superimposing the stresses caused by the uneven distribution of the internal temperature field and those caused by the incompatible thermal deformation among the different components in the surface concrete Before the erection of the upper structures,the absolute values of the tangential and vertical stresses were the same;therefore,only one curve was observed.From 22:00 to 8:00,the pier concrete surface was in tension,whereas from 11:00 to 22:00,the pier concrete surface was in compression.The surface of the pier concrete was subjected to biaxial forces of equal magnitude with a maximum compressive stress of 12.52 MPa and maximum tensile stress of 2.15 MPa,respectively at 18:00 and 8:00.According to the fatigue equation,the concrete was predicted to crack after 21 d of temperature cycling.Moreover,if humidity-induced stress is added on top of this,the tensile stress may approach or even exceed the concrete's tensile strength,thereby posing a significant risk of cracking.After the erection of upper structures,the tangential and vertical stresses no longer coincide because the upper structures have been erected.The curve of the tangential stress is unchanged,whereas the curve of the vertical stress is translated downwards by 1.57 MPa due to the structural deadweight.Therefore,the maximum tangential compressive stress remained 12.52 MPa,whereas the maximum vertical compressive stress increased to 14.09 MPa.Additionally,the maximum tangential tensile stress was 2.15 MPa,and the maximum vertical tensile stress was 0.58 MPa.According to Appendix C of GB/T 50010 and the fatigue equation,stresses are unlikely to cause cracking of the pier concrete surface.Although a higher CTE of the coarse aggregate slightly increased the maximum compressive stress,the differences among the three groups of concrete were minimal and could be ignored.Specifically,the maximum compressive stresses on the pier concrete surface were 12.54,12.45 MPa,and 12.56 MPa when using diorite,limestone,and basalt,respectively.By contrast,a lower CTE of the coarse aggregate results in a greater maximum tensile stress on the pier concrete surface.For example,when using limestone,which has a low CTE,the maximum tensile stress on the pier concrete surface is 2.28 MPa,compared to 2.17 MPa when using diorite and 2.14 MPa when using basalt.The finite element simulation results indicated that the maximum compressive stress on the pier concrete surface was 11.72 MPa,whereas the maximum tensile stress was 2.10 MPa.These results are approximately consistent with the theoretical calculations.This consistency provides mutual verification.Conclusions Surface cracking in pier concrete occurs predominantly before the erection of upper structures.Under sunny conditions,the orthogonal decomposition of the superficial stress revealed that the maximum compressive stress during the day was approximately 12.52 MPa,whereas the maximum tensile stress was approximately 2.15 MPa.This tensile stress approached the tensile strength of the C35 concrete under biaxial tension.The risk of cracking increased significantly when humidity-induced stress was considered.After the erection of upper structures,the maximum tangential tensile stress on the pier surface remained at 2.15 MPa while the maximum vertical stress decreased to 0.58 MPa,both of which are well below the tensile strength of C35 concrete under biaxial tension.Although the use of coarse aggregates with a lower coefficient of thermal expansion reduced the tensile stress induced by temperature gradients,it increased the stress owing to material deformation incompatibility,leading to a slight increase in the maximum tensile stress on the pier concrete surface.
基金supported by the Shihezi University High-Level Talents Research Startup Project(Project No.RCZK202521)the National Natural Science Foundation of China(Grant Nos.12271066,11871121,12171405)+1 种基金the Chongqing Natural Science Foundation Joint Fund for Innovation and Development Project(Project No.CSTB2024NSCQLZX0085)the Chongqing Normal University Foundation(Grant No.23XLB018).
文摘This paper investigates ruin,capital injection,and dividends for a two-dimensional risk model.The model posits that surplus levels of insurance companies are governed by a perturbed composite Poisson risk model.This model introduces a dependence between the two surplus levels,present in both the associated perturbations and the claims resulting from common shocks.Critical levels of capital injection and dividends are established for each of the two risks.The surplus levels are observed discretely at fixed intervals,guiding decisions on capital injection,dividends,and ruin at these junctures.This study employs a two-dimensional Fourier cosine series expansion method to approximate the finite time expected discounted operating cost until ruin.The ensuing approximation error is also quantified.The validity and accuracy of the method are corroborated through numerical examples.Furthermore,the research delves into the optimal capital allocation problem.
基金Supported by Projects from Chongqing Municipal Science and Technology Commission(CSTB2022NSCQ-MSX0445)。
文摘For the Sylvester continued fraction expansions of real numbers,FAN et al.(2007)proved that,for almost all real numbers,the nth partial quotient grows exponentially with respect to the product of the first n-1 partial quotients.In this paper,we establish the Hausdorff dimension of the exceptional set where the growth rate is a general function.
基金supported by the Fundamental Research Funds for the Central Universities(WK2090000055)Anhui Provincial Natural Science Foundation of China(2308085QG231).
文摘As a negative electrode material for lithium-ion batteries,silicon monoxide(SiO)suffers from dramatic volume changes during cycling,causing excessive stress within the electrode and resulting in electrode deformation and fragmentation.This ultimately leads to a decrease in cell capacity.The trends of volume expansion and capacity change of the SiO/graphite(SiO/C)composite electrode during cycling were investigated via in situ expansion monitoring.First,a series of expansion test schemes were designed,and the linear relationship between negative electrode expansion and cell capacity degradation was quantitatively analyzed.Then,the effects of different initial pressures on the long-term cycling performance of the cell were evaluated.Finally,the mechanism of their effects was analyzed by scanning electron microscope.The results show that after 50 cycles,the cell capacity decreases from 2.556 mAh to 1.689 mAh,with a capacity retention ratio(CRR)of only 66.08%.A linear relationship between the capacity retention ratio and thickness expansion was found.Electrochemical measurements and scanning electron microscope images demonstrate that intense stress inhibits the lithiation of the negative electrode and that the electrode is more susceptible to irreversible damage during cycling.Overall,these results reveal the relationship between the cycling performance of SiO and the internal pressure of the electrode from a macroscopic point of view,which provides some reference for the application of SiO/C composite electrodes in lithium-ion batteries.
基金Supported by the National Natural Science Foundation of China(12001249)the Natural Science Foundation of Jiangxi Province(20232BAB211004)the Educational Commission Science Programm of Jiangxi Province(GJJ2200523)。
文摘In this paper,we establish common fixed point theorems for expansive map?pings on b-metric-like space and coincidence point for f-weakly isotone increasing mappings in partially ordered b-metric-like space.The main results generalize and extend several well-known comparable results from the existing literature.Moreover,some examples are provided to illustrate the main results.
