In recent decades,capacitive pressure sensors(CPSs)with high sensitivity have demonstrated significant potential in applications such as medical monitoring,artificial intelligence,and soft robotics.Efforts to enhance ...In recent decades,capacitive pressure sensors(CPSs)with high sensitivity have demonstrated significant potential in applications such as medical monitoring,artificial intelligence,and soft robotics.Efforts to enhance this sensitivity have predominantly focused on material design and structural optimization,with surface microstructures such as wrinkles,pyramids,and micro-pillars proving effective.Although finite element modeling(FEM)has guided enhancements in CPS sensitivity across various surface designs,a theoretical understanding of sensitivity improvements remains underexplored.This paper employs sinusoidal wavy surfaces as a representative model to analytically elucidate the underlying mechanisms of sensitivity enhancement through contact mechanics.These theoretical insights are corroborated by FEM and experimental validations.Our findings underscore that optimizing material properties,such as Young’s modulus and relative permittivity,alongside adjustments in surface roughness and substrate thickness,can significantly elevate the sensitivity.The optimal performance is achieved when the amplitude-to-wavelength ratio(H/)is about 0.2.These results offer critical insights for designing ultrasensitive CPS devices,paving the way for advancements in sensor technology.展开更多
Fabricating damage tolerant porous ceramics with efficient energy absorption and impact-resistant capability has been a challenge because of the brittle nature of ceramic materials.In nature,mineralized tissues or org...Fabricating damage tolerant porous ceramics with efficient energy absorption and impact-resistant capability has been a challenge because of the brittle nature of ceramic materials.In nature,mineralized tissues or organisms such as cuttlebones and diatoms have evolved with hierarchical porous structures to overcome this difficulty.A bioinspired design of ceramic lattice structure with pores at multiple length scales,ranging from few nanometers to hundreds of micrometers,is proposed in the present work.These ceramic lattices with hierarchical porous structures were successfully fabricated via 3D cryogenic printing.Under quasi-static compressions,the printed ceramic lattices showed unprecedented long plateau strain(∼60%)and a specific energy absorption of∼10 kJ·kg^(−1) with a porosity of∼90%.The resulting energy absorption capability was comparable with most composites and metals,thus overcoming the brittle nature of traditional porous ceramics.This was attributed to the delayed destruction of the lattice structure,as well as the gradual collapse of pores at multiple length scales.Similar trends have also been observed under split Hopkinson pressure bar(SHPB)tests,indicating excellent energy absorption under high strain-rate impacts.The proposed 3D printing technique that produces hierarchical pores was also demonstrated to apply to other functional materials,such as silicon carbide,barium titanate,hydroxyapatite,and even titanium alloy,thus opening up new possibilities for fabricating bioinspired hierarchical porous structures.展开更多
A macroscopically nominal flat surface is rough at the nanoscale level and consists of nanoasperities.Therefore,the frictional properties of the macroscale-level rough surface are determined by the mechanical behavior...A macroscopically nominal flat surface is rough at the nanoscale level and consists of nanoasperities.Therefore,the frictional properties of the macroscale-level rough surface are determined by the mechanical behaviors of nanoasperity contact pairs under shear.In this work,we first used molecular dynamics simulations to study the non-adhesive shear between single contact pairs.Subsequently,to estimate the friction coefficient of rough surfaces,we implemented the frictional behavior of a single contact pair into a Greenwood-Williamson-type statistical model.By employing the present multiscale approach,we used the size,rate,and orientation effects,which originated from nanoscale dislocation plasticity,to determine the dependence of the macroscale friction coefficient on system parameters,such as the surface roughness,separation,loading velocity,and direction.Our model predicts an unconventional dependence of the friction coefficient on the normal contact load,which has been observed in nanoscale frictional tests.Therefore,this model represents one step toward understanding some of the relevant macroscopic phenomena of surface friction at the nanoscale level.展开更多
This article investigates the macroeconomic consequences of foreign asset-freezing sanctions,a tool utilized by several Western nations amid recent geopolitical tensions.Specifically,it examines the repercussions of s...This article investigates the macroeconomic consequences of foreign asset-freezing sanctions,a tool utilized by several Western nations amid recent geopolitical tensions.Specifically,it examines the repercussions of such sanctions on open economies,finding that they may experience a sharp recession and currency crisis.To quantify the impact,we develop a new Keynesian dynamic stochastic general equilibrium model with financial frictions and an asset-freezing channel for an open economy.We also calibrate our model to capture the unique structures of the Russian economy.The quantitative analysis of the model demonstrates that an abrupt asset-freezing sanction would lead to large output losses and high inflation increases.Our counterfactual examination reveals that higher elasticity of import substitution and lower elasticity of export substitution could alleviate the impact of foreign sanctions,whereas more aggressive monetary policy may have positive but limited stabilization effects.Notably,the monetary authority must navigate a trade-off between stabilizing output and managing inflation resulting from the cash-in-advance channel.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.12272369)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDB0620101).
文摘In recent decades,capacitive pressure sensors(CPSs)with high sensitivity have demonstrated significant potential in applications such as medical monitoring,artificial intelligence,and soft robotics.Efforts to enhance this sensitivity have predominantly focused on material design and structural optimization,with surface microstructures such as wrinkles,pyramids,and micro-pillars proving effective.Although finite element modeling(FEM)has guided enhancements in CPS sensitivity across various surface designs,a theoretical understanding of sensitivity improvements remains underexplored.This paper employs sinusoidal wavy surfaces as a representative model to analytically elucidate the underlying mechanisms of sensitivity enhancement through contact mechanics.These theoretical insights are corroborated by FEM and experimental validations.Our findings underscore that optimizing material properties,such as Young’s modulus and relative permittivity,alongside adjustments in surface roughness and substrate thickness,can significantly elevate the sensitivity.The optimal performance is achieved when the amplitude-to-wavelength ratio(H/)is about 0.2.These results offer critical insights for designing ultrasensitive CPS devices,paving the way for advancements in sensor technology.
基金supported by the National Natural Science Foundation of China(Grant No.52305359)the startup funding from the Huazhong University of Science and Technology,the Opening fund of the State Key Laboratory of Nonlinear Mechanics and Natural Science Foundation of Hubei Province(No.2023AFB141)。
文摘Fabricating damage tolerant porous ceramics with efficient energy absorption and impact-resistant capability has been a challenge because of the brittle nature of ceramic materials.In nature,mineralized tissues or organisms such as cuttlebones and diatoms have evolved with hierarchical porous structures to overcome this difficulty.A bioinspired design of ceramic lattice structure with pores at multiple length scales,ranging from few nanometers to hundreds of micrometers,is proposed in the present work.These ceramic lattices with hierarchical porous structures were successfully fabricated via 3D cryogenic printing.Under quasi-static compressions,the printed ceramic lattices showed unprecedented long plateau strain(∼60%)and a specific energy absorption of∼10 kJ·kg^(−1) with a porosity of∼90%.The resulting energy absorption capability was comparable with most composites and metals,thus overcoming the brittle nature of traditional porous ceramics.This was attributed to the delayed destruction of the lattice structure,as well as the gradual collapse of pores at multiple length scales.Similar trends have also been observed under split Hopkinson pressure bar(SHPB)tests,indicating excellent energy absorption under high strain-rate impacts.The proposed 3D printing technique that produces hierarchical pores was also demonstrated to apply to other functional materials,such as silicon carbide,barium titanate,hydroxyapatite,and even titanium alloy,thus opening up new possibilities for fabricating bioinspired hierarchical porous structures.
文摘A macroscopically nominal flat surface is rough at the nanoscale level and consists of nanoasperities.Therefore,the frictional properties of the macroscale-level rough surface are determined by the mechanical behaviors of nanoasperity contact pairs under shear.In this work,we first used molecular dynamics simulations to study the non-adhesive shear between single contact pairs.Subsequently,to estimate the friction coefficient of rough surfaces,we implemented the frictional behavior of a single contact pair into a Greenwood-Williamson-type statistical model.By employing the present multiscale approach,we used the size,rate,and orientation effects,which originated from nanoscale dislocation plasticity,to determine the dependence of the macroscale friction coefficient on system parameters,such as the surface roughness,separation,loading velocity,and direction.Our model predicts an unconventional dependence of the friction coefficient on the normal contact load,which has been observed in nanoscale frictional tests.Therefore,this model represents one step toward understanding some of the relevant macroscopic phenomena of surface friction at the nanoscale level.
基金the National Natural Science Foundation of China(Nos.72150003 and 72125007).
文摘This article investigates the macroeconomic consequences of foreign asset-freezing sanctions,a tool utilized by several Western nations amid recent geopolitical tensions.Specifically,it examines the repercussions of such sanctions on open economies,finding that they may experience a sharp recession and currency crisis.To quantify the impact,we develop a new Keynesian dynamic stochastic general equilibrium model with financial frictions and an asset-freezing channel for an open economy.We also calibrate our model to capture the unique structures of the Russian economy.The quantitative analysis of the model demonstrates that an abrupt asset-freezing sanction would lead to large output losses and high inflation increases.Our counterfactual examination reveals that higher elasticity of import substitution and lower elasticity of export substitution could alleviate the impact of foreign sanctions,whereas more aggressive monetary policy may have positive but limited stabilization effects.Notably,the monetary authority must navigate a trade-off between stabilizing output and managing inflation resulting from the cash-in-advance channel.
