As the size of transistors shrinks and power density increases,thermal simulation has become an indispensable part of the device design procedure.However,existing works for advanced technology transistors use simplifi...As the size of transistors shrinks and power density increases,thermal simulation has become an indispensable part of the device design procedure.However,existing works for advanced technology transistors use simplified empirical models to calculate effective thermal conductivity in the simulations.In this work,we present a dataset of size-dependent effective thermal conductivity with electron and phonon properties extracted from ab initio computations.Absolute in-plane and cross-plane thermal conductivity data of eight semiconducting materials(Si,Ge,GaN,AlN,4H-SiC,GaAs,InAs,BAs)and four metallic materials(Al,W,TiN,Ti)with the characteristic length ranging from 5 nm to 50 nm have been provided.Besides the absolute value,normalized effective thermal conductivity is also given,in case it needs to be used with updated bulk thermal conductivity in the future.展开更多
The size-dependent effect on the biaxial and shear nonlinear buckling analysis of an isotropic and orthotropic micro-plate based on the surface stress, the modified couple stress theory （MCST）, and the nonlocal elas...The size-dependent effect on the biaxial and shear nonlinear buckling analysis of an isotropic and orthotropic micro-plate based on the surface stress, the modified couple stress theory （MCST）, and the nonlocal elasticity theories using the differential quadrature method （DQM） is presented. Main advantages of the MCST over the classical theory （CT） are the inclusion of the asymmetric couple stress tensor and the consideration of only one material length scale parameter. Based on the nonlinear von Karman assumption, the governing equations of equilibrium for the micro-classical plate consid- ering midplane displacements are derived based on the minimum principle of potential energy. Using the DQM, the biaxial and shear critical buckling loads of the micro-plate for various boundary conditions are obtained. Accuracy of the obtained results is validated by comparing the solutions with those reported in the literature. A parametric study is conducted to show the effects of the aspect ratio, the side-to-thickness ratio, Eringen＇s nonlocal parameter, the material length scale parameter, Young＇s modulus of the surface layer, the surface residual stress, the polymer matrix coefficients, and various boundary conditions on the dimensionless uniaxial, biaxial, and shear critical buckling loads. The results indicate that the critical buckling loads are strongly sensitive to Eringen＇s nonlocal parameter, the material length scale parameter, and the surface residual stress effects, while the effect of Young＇s modulus of the surface layer on the critical buckling load is negligible. Also, considering the size dependent effect causes the increase in the stiffness of the orthotropic micro-plate. The results show that the critical biaxial buckling load increases with an increase in G12/E2 and vice versa for E1/E2. It is shown that the nonlinear biaxial buckling ratio decreases as the aspect ratio increases and vice versa for the buckling amplitude. Because of the most lightweight micro-composite materials with high strength/weight and stiffness/weight ratios, it is anticipated that the results of the present work are useful in experimental characterization of the mechanical properties of micro-composite plates in the aircraft industry and other engineering applications.展开更多
This study investigates the surface effects on the operation of double-ended dislocation sources in single-crystal micropillars under compression.A comprehensive theoretical framework is formulated to derive the stres...This study investigates the surface effects on the operation of double-ended dislocation sources in single-crystal micropillars under compression.A comprehensive theoretical framework is formulated to derive the stress field of the source segment and the corresponding Peach-Koehler(PK)forces acting on this segment near the free surfaces.An analytical formulation is then developed to compare the source strength with and without the influence of the surface stress.The results reveal that the surface effects on the dislocation source strength are highly sensitive to the interplay between the source length and its distance from the free surface.These surface effects can either enhance or reduce the critical stress required for the source operation by up to 50%,leading to significant fluctuations in yield strength,as commonly observed in discrete dislocation dynamics simulations and experimental studies.These findings provide different interpretations for the size-dependent and stochastic yield stress behavior in face-centered cubic(FCC)micropillars.展开更多
In this study,the thermodynamic behaviors of the intrinsic frequency and buckling temperature of rectangular plates of functionally graded materials(FGMs)are explored based on the modified couple stress theory(MCST)an...In this study,the thermodynamic behaviors of the intrinsic frequency and buckling temperature of rectangular plates of functionally graded materials(FGMs)are explored based on the modified couple stress theory(MCST)and the novel dual powerlaw scale distribution theory.The effects of linear,homogeneous,and non-homogeneous temperature fields on the frequency and buckling temperature of FGM microplates are evaluated in detail.The results show that the porosity greatly affects the mechanical properties of FGM plates,reducing their frequency and flexural temperature compared with non-porous plates.Different temperature profiles alter plate frequencies and buckling temperatures.The presence and pattern of scale effect parameters are also shown to be crucial for the mechanical response of FGM plates.The present research aims to provide precise guidelines for the micro-electro-mechanical system(MEMS)fabrication by elucidating the complex interplay between thermal,material,and structural factors that affect the performance of FGM plates in advanced applications.展开更多
This paper examined how microstructure influences the homogenized thermal conductivity of cellular structures and revealed a surface-induced size-dependent effect.This effect is linked to the porous microstructural fe...This paper examined how microstructure influences the homogenized thermal conductivity of cellular structures and revealed a surface-induced size-dependent effect.This effect is linked to the porous microstructural features of cellular structures,which stems from the degree of porosity and the distri-bution of the pores.Unlike the phonon-driven surface effect at the nanoscale,the macro-scale surface mechanism in thermal cellular structures is found to be the microstructure-induced changes in the heat conduction path based on fully resolved 3D numerical simulations.The surface region is determined by the microstructure,characterized by the intrinsic length.With the coupling between extrinsic and intrinsic length scales under the surface mechanism,a surface-enriched multiscale method was devel-oped to accurately capture the complex size-dependent thermal conductivity.The principle of scale separation required by classical multiscale methods is not necessary to be satisfied by the proposed multiscale method.The significant potential of the surface-enriched multiscale method was demon-strated through simulations of the effective thermal conductivity of a thin-walled metamaterial struc-ture.The surface-enriched multiscale method offers higher accuracy compared with the classical multiscale method and superior efficiency over high-fidelity finite element methods.展开更多
In this paper,a fractional-order kinematic model is utilized to capture the size-dependent static bending and free vibration responses of piezoelectric nanobeams.The general nonlocal strains in the Euler-Bernoulli pie...In this paper,a fractional-order kinematic model is utilized to capture the size-dependent static bending and free vibration responses of piezoelectric nanobeams.The general nonlocal strains in the Euler-Bernoulli piezoelectric beam are defined by a frame-invariant and dimensionally consistent Riesz-Caputo fractional-order derivatives.The strain energy,the work done by external loads,and the kinetic energy based on the fractional-order kinematic model are derived and expressed in explicit forms.The boundary conditions for the nonlocal Euler-Bernoulli beam are derived through variational principles.Furthermore,a finite element model for the fractional-order system is developed in order to obtain the numerical solutions to the integro-differential equations.The effects of the fractional order and the vibration order on the static bending and vibration responses of the Euler-Bernoulli piezoelectric beams are investigated numerically.The results from the present model are validated against the existing results in the literature,and it is demonstrated that they are theoretically consistent.Although this fractional finite element method(FEM)is presented in the context of a one-dimensional(1D)beam,it can be extended to higher dimensional fractional-order boundary value problems.展开更多
This paper extends the one-dimensional(1D)nonlocal strain gradient integral model(NStraGIM)to the two-dimensional(2D)Kirchhoff axisymmetric nanoplates,based on nonlocal strain gradient integral relations formulated al...This paper extends the one-dimensional(1D)nonlocal strain gradient integral model(NStraGIM)to the two-dimensional(2D)Kirchhoff axisymmetric nanoplates,based on nonlocal strain gradient integral relations formulated along both the radial and circumferential directions.By transforming the proposed integral constitutive equations into the equivalent differential forms,complemented by the corresponding constitutive boundary conditions(CBCs),a well-posed mathematical formulation is established for analyzing the axisymmetric bending and buckling of annular/circular functionally graded(FG)sandwich nanoplates.The boundary conditions at the inner edge of a solid nanoplate are derived by L'H?spital's rule.The numerical solution is obtained by the generalized differential quadrature method(GDQM).The accuracy of the proposed model is validated through comparison with the data from the existing literature.A parameter study is conducted to demonstrate the effects of FG sandwich parameters,size parameters,and nonlocal gradient parameters.展开更多
Strong metal-support interaction(SMSI)has a great impact on the activity and selectivity of heterogeneous catalysts,which was usually adjusted by changing reduction temperature or processing catalyst in different atmo...Strong metal-support interaction(SMSI)has a great impact on the activity and selectivity of heterogeneous catalysts,which was usually adjusted by changing reduction temperature or processing catalyst in different atmosphere.However,few researches concentrate on modulating SMSI through regulating the structure of the support.Herein,we show how changing the surface environment of the anatase TiO_(2)(B–TiO_(2))can be used to modulate the SMSI.The moderate TiOx overlayer makes the Ni metal highly dispersed on the high specific surface area of support,resulting in a substantially enhanced CO_(2)methanation rate.Besides,a novel phenomenon was observed that boron dopants promote the for-mation of the B–O–Ti interface site,enhancing the catalytic performance of CO_(2)hydrogenation.DFT calculations confirm that the B–O–Ti structure facilitates the activation of CO_(2)and further hydrogenation to methane.展开更多
The classical piezoelectric theory fails to capture the size-dependent electromechanical coupling behaviors of piezoelectric microstructures due to the lack of material length-scale parameters.This study presents the ...The classical piezoelectric theory fails to capture the size-dependent electromechanical coupling behaviors of piezoelectric microstructures due to the lack of material length-scale parameters.This study presents the constitutive relations of a piezoelectric material in terms of irreducible transversely isotropic tensors that include material length-scale parameters.Using these relations and the general strain gradient theory,a size-dependent bending model is proposed for a bilayer cantilever microbeam consisting of a transversely isotropic piezoelectric layer and an isotropic elastic layer.Analytical solutions are provided for bilayer cantilever microbeams subjected to force load and voltage load.The proposed model can be simplified to the model incorporating only partial strain gradient effects.This study examines the effect of strain gradient by comparing the normalized electric potentials and deflections of different models.Numerical results show that the proposed model effectively captures size effects in piezoelectric microbeams,whereas simplified models underestimate size effects due to ignoring partial strain gradient effects.展开更多
Summary： The contribution of particles to cardiovascular mortality and morbidity has been enlightened by epidemiologic and experimental studies. However, adverse biological effects of the particles with different siz...Summary： The contribution of particles to cardiovascular mortality and morbidity has been enlightened by epidemiologic and experimental studies. However, adverse biological effects of the particles with different sizes on cardiovascular cells have not been well recognized. In this study, sub-cultured human umbilical vein endothelial cells （HUVECs） were exposed to increasing concentrations of pure quartz particles （DQ） of three sizes （DQPM1, 〈1 μm; DQPM3-5, 3-5 μm; DQPM5, 5 μm） and carbon black particles of two sizes （CB0.1, 〈0.1 μm; CB 1, 〈 1 μm） for 24 h. Cytotoxicity was estimated by measuring the activity of lactate dehydrogenase （LDH） and cell viability. Nitric oxide （NO） generation and cyto- kines （TNF-α and IL-1β） releases were analyzed by using NO assay and enzyme-linked immunoabsorbent assay （ELISA）, respectively. It was found that both particles induced adverse biological effects on HUVECs in a dose-dependent manner. The size of particle directly influenced the biological activity. For quartz, the smaller particles induced stronger cytotoxicity and higher levels of cytokine responses than those particles of big size. For carbon black particles, CB0.1 was more capable of inducing adverse responses on HUVECs than CB 1 only at lower particle concentrations, in contrast to those at higher concentrations. Meanwhile, our data also revealed that quartz particles performed stronger cell damage and produced higher levels of TNF-α than carbon black particles, even if particles size was similar. In conclusion, particle size as well as particle composition should be both considered in assessing vascular endothelial cells injury and inflammation responses induced by particles.展开更多
Al-Mg-Si-Sc alloys with different Mg/Si ratio(<1.73 in wt.% vs>1.73 in wt.%) and different grain size(coarse grains vs ultrafine grains) were prepared, which allowed to investigate the grain size-dependent Mg/Si...Al-Mg-Si-Sc alloys with different Mg/Si ratio(<1.73 in wt.% vs>1.73 in wt.%) and different grain size(coarse grains vs ultrafine grains) were prepared, which allowed to investigate the grain size-dependent Mg/Si ratio effect on the microstructural evolution and concomitantly on the hardness and electrical conductivity when subjected to aging at 200℃. In the coarse-grained Al-Mg-Sc-Sc alloys, the β" precipitation within the grain interior and also the precipitation hardening were highly dependent on the Mg/Si ratio,while the electrical conductivity was slightly affected by the Mg/Si ratio. A promoted β" precipitation was found in the case of Si excess(Mg/Si ratio <1.73), much greater than in the case of Mg excess(Mg/Si ratio>1.73). While in the ultrafine-grained Al-Mg-Si-Sc alloys, the electrical conductivity rather than the hardness was more sensitive to the Mg/Si ratio. The alloy with Si excess displayed electrical conductivity much higher than its counterpart with Mg excess. This is rationalized by the grain boundary precipitation promoted by Si, which reduced the solute atoms and precipitates within the grain interior. Age softening was found in the ultrafine-grained alloy with Si excess, but the ultrafine-grained alloy with Mg excess held the hardness almost unchanged during the aging. The hardness-conductivity correlation is comprehensively discussed by considering the coupling effect of Mg/Si ratio and grain size. A strategy to simultaneously increase the hardness/strength and electrical conductivity is proposed for the Al-Mg-SiSc alloys, based on present understanding of the predominant factors on strengthening and conductivity,respectively.展开更多
A size-dependent continuum-based model is developed for the functionally graded(FG)Timoshenko micro-beams with viscoelastic properties,in which material parameters vary according to the power law along its axial direc...A size-dependent continuum-based model is developed for the functionally graded(FG)Timoshenko micro-beams with viscoelastic properties,in which material parameters vary according to the power law along its axial direction.The size effect is incorporated by employing the modified couple stress theory and Kelvin-Voigt viscoelastic model,so that viscous components are included in the stress and the deviatoric segments of the symmetric couple stress tensors.The components of strain,curvature,stress and couple stress are formulated by combining them with the Timoshenko beam theory.Based on the Hamilton principle,the governing differential equations and boundary conditions for the micro-beam are expressed with arbitrary beam section shape and arbitrary type of loads.The size effect,FG effect,Poisson effect,and the influence of the beam section shape on the mechanical behaviors of viscoelastic FG micro-beams are investigated by taking the simply supported micro-beam subjected to point load as an example.Results show that the size effect on deflection,normal stress and couple stress are obvious when the size of the micro-beam is small enough,and the FG effects are obvious when the size of the micro-beam is large enough.Moreover,the Poisson ratio influences the size effect significantly and the beam section shape is also an important factor influencing the mechanical behavior of the micro-beam.展开更多
Tree mortality significantly influences forest structure and function,yet our understanding of its dynamic patterns among a range of tree sizes and among different plant functional types(PFTs)remains incomplete.This s...Tree mortality significantly influences forest structure and function,yet our understanding of its dynamic patterns among a range of tree sizes and among different plant functional types(PFTs)remains incomplete.This study analysed size-dependent tree mortality in a temperate forest,encompassing 46 tree species and 32,565 individuals across different PFTs(i.e.,evergreen conifer vs.deciduous broadleaf species,shade-tolerant vs.shade-intolerant species).By employing all-subset regression procedures and logistic generalized linear mixed-effects models,we identified distinct mortality patterns influenced by biotic and abiotic factors.Our results showed a stable mortality patte rn in eve rgreen conifer species,contrasted by a declining pattern in deciduous broadleaf and shadetolerant,as well as shade-intolerant species,across size classes.The contribution to tree mortality of evergreen conifer species shifted from abiotic to biotic factors with increasing size,while the mortality of deciduous broadleaf species was mainly influenced by biotic factors,such as initial diameter at breast height(DBH)and conspecific negative density.For shade-tolerant species,the mortality of small individuals was mainly determined by initial DBH and conspecific negative density dependence,whereas the mortality of large individuals was subjected to the combined effect of biotic(competition from neighbours)and abiotic factors(i.e.,convexity and pH).As for shade-intolerant species,competition from neighbours was found to be the main driver of tree mortality throughout their growth stages.Thus,these insights enhance our understanding of forest dynamics by revealing the size-dependent and PFT-specific tree mortality patterns,which may inform strategies for maintaining forest diversity and resilience in temperate forest ecosystems.展开更多
The non-Hermitian systems with the non-Hermitian skin effect(NHSE)are very sensitive to the imposed boundary conditions and lattice sizes,which lead to size-dependent non-Hermitian skin effects.Here,we report the expe...The non-Hermitian systems with the non-Hermitian skin effect(NHSE)are very sensitive to the imposed boundary conditions and lattice sizes,which lead to size-dependent non-Hermitian skin effects.Here,we report the experimental observation of NHSE with different boundary conditions and different lattice sizes in the unidirectional hopping model based on a circuit platform.The circuit admittance spectra and corresponding eigenstates are very sensitive to the presence of the boundary.Meanwhile,our experimental results show how the lattice sizes and boundary terms together affect the strength of NHSE.Therefore,our electric circuit provides a good platform to observe size-dependent boundary effects in non-Hermitian systems.展开更多
Metastable high entropy alloys(HEAs) and amorphous metallic glasses(MGs), with the chemical disordered character, are intensively studied due to their excellent performance. Here, we introduce Cu to separately constra...Metastable high entropy alloys(HEAs) and amorphous metallic glasses(MGs), with the chemical disordered character, are intensively studied due to their excellent performance. Here, we introduce Cu to separately constrain these two metastable materials and comparatively investigate their deformation behaviors and mechanical properties of Cu/HEA Fe Co Cr Ni and Cu/MG Cu Zr nanolaminated micropillars in terms of intrinsic layer thickness h and extrinsic pillar diameter D. The metastable HEA layers, as the hard phase in Cu/HEA micropillars, are stable and dominate the deformation, while transformation(crystallization) occurs in MG which plays a minor role in deformation of Cu/MG micropillars. The h-controlled deformation mode transits from the D-independent homogenous-like deformation at large h to the Ddependent shear banding at small h in both Cu/HEA and Cu/MG micropillars. Although both Cu/HEA and Cu/MG micropillars exhibit a maximum strain hardening capability controlled by h, the former manifests much lower hardening capability compared with the latter. The intrinsic size h and extrinsic size D have a strong coupling effect on the strength of Cu/HEA and Cu/MG micropillars. The strength of strength of Cu/HEA micropillars exhibits the D-dependent transition from "smaller is stronger" to "smaller is weaker"with increasing h. By contrast, the strength of Cu/MG micropillars exhibits the transition from bulk-like D-independent behavior at large h to small volume D-dependent behavior(smaller is stronger) at small h.展开更多
Electrochemical ozone production(EOP) via water electrolysis represents an attractive method for the generation of high-purity O3. Herein, the X-PtZn/Zn-N-C electrocatalysts show a strong structural sensitive behavior...Electrochemical ozone production(EOP) via water electrolysis represents an attractive method for the generation of high-purity O3. Herein, the X-PtZn/Zn-N-C electrocatalysts show a strong structural sensitive behavior depends on the size of the PtZn nanoparticles and their EOP activity exhibits a volcano-type dependence for the O3 performance in neutral media. The 7.7-PtZn/Zn-N-C exhibits EOP current efficiency of 4.2%, and shows the prominent performance in the production of gaseous O3 with a value of 1647 ppb at 30 min, which is almost 4-fold compared to 2.2-Pt Zn/Zn-N-C. Based on the experiments and theoretical calculations, the performance of the EOP process was determined by the nanoparticle size-effect and the synergistic effect between the PtZn nanoparticles and atomically dispersed Zn-N-C. Furthermore, the fivemembered cyclic structure of O3 can be stabilized between the PtZn nanoparticle and the Zn-N-C support,indicating that O3 is produced at the interface.展开更多
Piezoelectric superlattice is a potential component for nanoelectromechanical systems. Due to the strong nonlocal effect such as flexoelectric effect at interfaces, classical piezoelectric theory is unable to accurate...Piezoelectric superlattice is a potential component for nanoelectromechanical systems. Due to the strong nonlocal effect such as flexoelectric effect at interfaces, classical piezoelectric theory is unable to accurately describe the electromechanical response of piezoelectric superlattice at nanoscale scale. Based on the previous nonlocal thermodynamics theory with flexoelectric effect Liu et al. （2016）, the size- dependent electromechanical properties of piezoelectric superlattices made of BaTiO3 （BTO） and PbTiO3 （PRO） layers are investigated systematically in the present work. Giant strain gradient is found near the interface between BTO and PTO layers, which leads to the significant enhancement of polarization in the superlattice due to the flexoelectric effect. For the piezoelectric BTO-PTO superlattices with different unit- cell sizes, the thickness of interface with nontrivial strain gradient is almost constant. The influence of strain gradient at the interface becomes significant when the size of superlattice decreases, As a result, a strong size dependence of electromechanical properties is predicted for the piezoelectric BTO-PTO superlattices, In particular, for the superlattices with a specific thickness ratio of BTO and PTO layers, the piezoelectric response can be several times larger than that of bulk structure. The present work demonstrates a practical wast to design the piezoelectric superlattices with high piezoelectric coefficient by using the nonlocal effect at nanoscale.展开更多
The flexoelectric effect refers to the electromechanical coupling between electric polarization and mechanical strain gradient.It universally exists in a variety of materials in any space group,such as liquid crystals...The flexoelectric effect refers to the electromechanical coupling between electric polarization and mechanical strain gradient.It universally exists in a variety of materials in any space group,such as liquid crystals,dielectrics,biological materials,and semiconductors.Because of its unique size effect,nanoscale flexoelectricity has shown novel phenomena and promising applications in electronics,optronics,mechatronics,and photovoltaics.In this review,we provide a succinct report on the discovery and development of the flexoelectric effect,focusing on flexoelectric materials and related applications.Finally,we discuss recent flexoelectric research progress and still‐unsolved problems.展开更多
Agricultural intensification has led to an increase in monoculture and the use of chemical pesticides,resulting in a decline in biodiversity and a reduction in ecosystem services,particularly biological pest managemen...Agricultural intensification has led to an increase in monoculture and the use of chemical pesticides,resulting in a decline in biodiversity and a reduction in ecosystem services,particularly biological pest management.However,studies have shown that agroforestry can not only improve land productivity and biodiversity but also regulate some ecosystem services.This study reviews the impacts of physical and biological factors on herbivorous pests,parasites,and predatory natural enemies in fruit-crop agroforestry systems.Fruit-crop agroforestry systems provide high spatial heterogeneity by altering crop layouts,regulating the microclimate and soil quality,and offering food resources and shelter for natural enemies,thus promoting biological pest control.This enhances biological control and makes the agrocomplex system an effective tool for sustainable agriculture.Our research shows that volatile plant substances attract or repel pests and natural enemies based on the characteristics of the insects themselves.When scientifically designed,fruit-crop agroforestry systems provide high spatial heterogeneity and favorable microclimatic conditions,which enhance biological pest control and make the agroforestry system an effective tool for sustainable agriculture.Our research shows that fruit-crop agroforestry systems can provide richer food resources and habitat,enhancing biological pest control and improving pest management.展开更多
Liver cancer is the fourth cause of cancer-related deaths and the primary cause of death in patients with compensated cirrhosis.In recent years,the role of traditional Chinese medicine in the treatment of liver cancer...Liver cancer is the fourth cause of cancer-related deaths and the primary cause of death in patients with compensated cirrhosis.In recent years,the role of traditional Chinese medicine in the treatment of liver cancer has attracted more and more attention and recognition.Luteolin(LUT)and glycyrrhetinic(GA)are natural compounds extracted from Chinese herbal medicine.LUT exhibits various biological activity including anti-inflammatory,antibacterial,antiviral,anti-tumor,and neuroprotective effects.GA significantly inhibits the growth and metastasis of cancer cells.However,the low water solubility of both compounds hinders their clinical applications.In this study,rod-shaped nanoparticles(NPs)self-assembled from LUT and GA were designed to enhance drug solubility and tumor-targeting capability.We verified that the assembly mechanism of the NPs was π-π stacking.These NPs significantly inhibited the proliferation of liver cancer cells while had no significant effect on normal liver cells.In a mouse model of liver cancer,these NPs demonstrated superior tumor-targeting ability due to the enhanced permeability and retention effect,and the affinity of GA for liver cancer cells,resulting in better therapeutic efficacy with lower systemic toxicity.Results of network pharmacology analysis showed that LUT and GA respectively targeted estrogen receptor 1(ESR1)protein and cyclin-dependent kinase 1(CDK1)protein to corporately induce tumor cell cycle arrest,which induced the inhibition of tumor cell proliferation.In conclusion,this study provides a novel reference for the treatment of liver cancer.展开更多
基金Project supported by the National Key R&D Project from Ministry of Science and Technology of China(Grant No.2022YFA1203100)the National Natural Science Foundation of China(Grant No.52122606)the funding from Shanghai Polytechnic University.
文摘As the size of transistors shrinks and power density increases,thermal simulation has become an indispensable part of the device design procedure.However,existing works for advanced technology transistors use simplified empirical models to calculate effective thermal conductivity in the simulations.In this work,we present a dataset of size-dependent effective thermal conductivity with electron and phonon properties extracted from ab initio computations.Absolute in-plane and cross-plane thermal conductivity data of eight semiconducting materials(Si,Ge,GaN,AlN,4H-SiC,GaAs,InAs,BAs)and four metallic materials(Al,W,TiN,Ti)with the characteristic length ranging from 5 nm to 50 nm have been provided.Besides the absolute value,normalized effective thermal conductivity is also given,in case it needs to be used with updated bulk thermal conductivity in the future.
基金supported by the Iranian Nanotechnology Development Committee and the University of Kashan(No.363452/10)
文摘The size-dependent effect on the biaxial and shear nonlinear buckling analysis of an isotropic and orthotropic micro-plate based on the surface stress, the modified couple stress theory （MCST）, and the nonlocal elasticity theories using the differential quadrature method （DQM） is presented. Main advantages of the MCST over the classical theory （CT） are the inclusion of the asymmetric couple stress tensor and the consideration of only one material length scale parameter. Based on the nonlinear von Karman assumption, the governing equations of equilibrium for the micro-classical plate consid- ering midplane displacements are derived based on the minimum principle of potential energy. Using the DQM, the biaxial and shear critical buckling loads of the micro-plate for various boundary conditions are obtained. Accuracy of the obtained results is validated by comparing the solutions with those reported in the literature. A parametric study is conducted to show the effects of the aspect ratio, the side-to-thickness ratio, Eringen＇s nonlocal parameter, the material length scale parameter, Young＇s modulus of the surface layer, the surface residual stress, the polymer matrix coefficients, and various boundary conditions on the dimensionless uniaxial, biaxial, and shear critical buckling loads. The results indicate that the critical buckling loads are strongly sensitive to Eringen＇s nonlocal parameter, the material length scale parameter, and the surface residual stress effects, while the effect of Young＇s modulus of the surface layer on the critical buckling load is negligible. Also, considering the size dependent effect causes the increase in the stiffness of the orthotropic micro-plate. The results show that the critical biaxial buckling load increases with an increase in G12/E2 and vice versa for E1/E2. It is shown that the nonlinear biaxial buckling ratio decreases as the aspect ratio increases and vice versa for the buckling amplitude. Because of the most lightweight micro-composite materials with high strength/weight and stiffness/weight ratios, it is anticipated that the results of the present work are useful in experimental characterization of the mechanical properties of micro-composite plates in the aircraft industry and other engineering applications.
基金supported by the Henan International Science and Technology Cooperation Program(No.242102521055)the Japan Science and Technology Agency(No.JPMJCR2092)the Japan Society for the Promotion of Science(Nos.JP24H00283,JP24K21575,and JP22K18754)。
文摘This study investigates the surface effects on the operation of double-ended dislocation sources in single-crystal micropillars under compression.A comprehensive theoretical framework is formulated to derive the stress field of the source segment and the corresponding Peach-Koehler(PK)forces acting on this segment near the free surfaces.An analytical formulation is then developed to compare the source strength with and without the influence of the surface stress.The results reveal that the surface effects on the dislocation source strength are highly sensitive to the interplay between the source length and its distance from the free surface.These surface effects can either enhance or reduce the critical stress required for the source operation by up to 50%,leading to significant fluctuations in yield strength,as commonly observed in discrete dislocation dynamics simulations and experimental studies.These findings provide different interpretations for the size-dependent and stochastic yield stress behavior in face-centered cubic(FCC)micropillars.
基金Project supported by the National Key Research and Development Program of China(No.2022YFB3207100)Hubei Provincial Strategic Scientist Training Plan(No.2022EJD009)the Fundamental Research Funds for the Central Universities of China(No.2042023kf1041)。
文摘In this study,the thermodynamic behaviors of the intrinsic frequency and buckling temperature of rectangular plates of functionally graded materials(FGMs)are explored based on the modified couple stress theory(MCST)and the novel dual powerlaw scale distribution theory.The effects of linear,homogeneous,and non-homogeneous temperature fields on the frequency and buckling temperature of FGM microplates are evaluated in detail.The results show that the porosity greatly affects the mechanical properties of FGM plates,reducing their frequency and flexural temperature compared with non-porous plates.Different temperature profiles alter plate frequencies and buckling temperatures.The presence and pattern of scale effect parameters are also shown to be crucial for the mechanical response of FGM plates.The present research aims to provide precise guidelines for the micro-electro-mechanical system(MEMS)fabrication by elucidating the complex interplay between thermal,material,and structural factors that affect the performance of FGM plates in advanced applications.
基金supported by the National Key Research and Development Program of China(Grant No.2021YFB1714600)the National Natural Science Foundation of China(Grant No.52175095)the Young Top-Notch Talent Cultivation Program of Hubei Province of China.
文摘This paper examined how microstructure influences the homogenized thermal conductivity of cellular structures and revealed a surface-induced size-dependent effect.This effect is linked to the porous microstructural features of cellular structures,which stems from the degree of porosity and the distri-bution of the pores.Unlike the phonon-driven surface effect at the nanoscale,the macro-scale surface mechanism in thermal cellular structures is found to be the microstructure-induced changes in the heat conduction path based on fully resolved 3D numerical simulations.The surface region is determined by the microstructure,characterized by the intrinsic length.With the coupling between extrinsic and intrinsic length scales under the surface mechanism,a surface-enriched multiscale method was devel-oped to accurately capture the complex size-dependent thermal conductivity.The principle of scale separation required by classical multiscale methods is not necessary to be satisfied by the proposed multiscale method.The significant potential of the surface-enriched multiscale method was demon-strated through simulations of the effective thermal conductivity of a thin-walled metamaterial struc-ture.The surface-enriched multiscale method offers higher accuracy compared with the classical multiscale method and superior efficiency over high-fidelity finite element methods.
基金Project supported by the National Natural Science Foundation of China(No.12172169)。
文摘In this paper,a fractional-order kinematic model is utilized to capture the size-dependent static bending and free vibration responses of piezoelectric nanobeams.The general nonlocal strains in the Euler-Bernoulli piezoelectric beam are defined by a frame-invariant and dimensionally consistent Riesz-Caputo fractional-order derivatives.The strain energy,the work done by external loads,and the kinetic energy based on the fractional-order kinematic model are derived and expressed in explicit forms.The boundary conditions for the nonlocal Euler-Bernoulli beam are derived through variational principles.Furthermore,a finite element model for the fractional-order system is developed in order to obtain the numerical solutions to the integro-differential equations.The effects of the fractional order and the vibration order on the static bending and vibration responses of the Euler-Bernoulli piezoelectric beams are investigated numerically.The results from the present model are validated against the existing results in the literature,and it is demonstrated that they are theoretically consistent.Although this fractional finite element method(FEM)is presented in the context of a one-dimensional(1D)beam,it can be extended to higher dimensional fractional-order boundary value problems.
基金Project supported by the National Natural Science Foundation of China(No.12172169)the Priority Academic Program Development of Jiangsu Higher Education Institutions。
文摘This paper extends the one-dimensional(1D)nonlocal strain gradient integral model(NStraGIM)to the two-dimensional(2D)Kirchhoff axisymmetric nanoplates,based on nonlocal strain gradient integral relations formulated along both the radial and circumferential directions.By transforming the proposed integral constitutive equations into the equivalent differential forms,complemented by the corresponding constitutive boundary conditions(CBCs),a well-posed mathematical formulation is established for analyzing the axisymmetric bending and buckling of annular/circular functionally graded(FG)sandwich nanoplates.The boundary conditions at the inner edge of a solid nanoplate are derived by L'H?spital's rule.The numerical solution is obtained by the generalized differential quadrature method(GDQM).The accuracy of the proposed model is validated through comparison with the data from the existing literature.A parameter study is conducted to demonstrate the effects of FG sandwich parameters,size parameters,and nonlocal gradient parameters.
基金supported by National Natural Science Foundation of China(21773053)Advanced Talents Incubation Program of Hebei University(801260201019)+1 种基金Research Innovation Team of College of Chemistry and Environmental Science of Hebei University(hxkytd-py2102)the support of the High-Performance Computing Center of Hebei University。
文摘Strong metal-support interaction(SMSI)has a great impact on the activity and selectivity of heterogeneous catalysts,which was usually adjusted by changing reduction temperature or processing catalyst in different atmosphere.However,few researches concentrate on modulating SMSI through regulating the structure of the support.Herein,we show how changing the surface environment of the anatase TiO_(2)(B–TiO_(2))can be used to modulate the SMSI.The moderate TiOx overlayer makes the Ni metal highly dispersed on the high specific surface area of support,resulting in a substantially enhanced CO_(2)methanation rate.Besides,a novel phenomenon was observed that boron dopants promote the for-mation of the B–O–Ti interface site,enhancing the catalytic performance of CO_(2)hydrogenation.DFT calculations confirm that the B–O–Ti structure facilitates the activation of CO_(2)and further hydrogenation to methane.
基金supported by the National Key Research and Development Program of China(2018YFB0703500).
文摘The classical piezoelectric theory fails to capture the size-dependent electromechanical coupling behaviors of piezoelectric microstructures due to the lack of material length-scale parameters.This study presents the constitutive relations of a piezoelectric material in terms of irreducible transversely isotropic tensors that include material length-scale parameters.Using these relations and the general strain gradient theory,a size-dependent bending model is proposed for a bilayer cantilever microbeam consisting of a transversely isotropic piezoelectric layer and an isotropic elastic layer.Analytical solutions are provided for bilayer cantilever microbeams subjected to force load and voltage load.The proposed model can be simplified to the model incorporating only partial strain gradient effects.This study examines the effect of strain gradient by comparing the normalized electric potentials and deflections of different models.Numerical results show that the proposed model effectively captures size effects in piezoelectric microbeams,whereas simplified models underestimate size effects due to ignoring partial strain gradient effects.
基金supported by grants from the National Basic Research Program of China(No.2011CB503804)the National Natural Science Foundation of China(No.81372967)
文摘Summary： The contribution of particles to cardiovascular mortality and morbidity has been enlightened by epidemiologic and experimental studies. However, adverse biological effects of the particles with different sizes on cardiovascular cells have not been well recognized. In this study, sub-cultured human umbilical vein endothelial cells （HUVECs） were exposed to increasing concentrations of pure quartz particles （DQ） of three sizes （DQPM1, 〈1 μm; DQPM3-5, 3-5 μm; DQPM5, 5 μm） and carbon black particles of two sizes （CB0.1, 〈0.1 μm; CB 1, 〈 1 μm） for 24 h. Cytotoxicity was estimated by measuring the activity of lactate dehydrogenase （LDH） and cell viability. Nitric oxide （NO） generation and cyto- kines （TNF-α and IL-1β） releases were analyzed by using NO assay and enzyme-linked immunoabsorbent assay （ELISA）, respectively. It was found that both particles induced adverse biological effects on HUVECs in a dose-dependent manner. The size of particle directly influenced the biological activity. For quartz, the smaller particles induced stronger cytotoxicity and higher levels of cytokine responses than those particles of big size. For carbon black particles, CB0.1 was more capable of inducing adverse responses on HUVECs than CB 1 only at lower particle concentrations, in contrast to those at higher concentrations. Meanwhile, our data also revealed that quartz particles performed stronger cell damage and produced higher levels of TNF-α than carbon black particles, even if particles size was similar. In conclusion, particle size as well as particle composition should be both considered in assessing vascular endothelial cells injury and inflammation responses induced by particles.
基金financially supported by the National Natural Science Foundation of China (No. 51771147)
文摘Al-Mg-Si-Sc alloys with different Mg/Si ratio(<1.73 in wt.% vs>1.73 in wt.%) and different grain size(coarse grains vs ultrafine grains) were prepared, which allowed to investigate the grain size-dependent Mg/Si ratio effect on the microstructural evolution and concomitantly on the hardness and electrical conductivity when subjected to aging at 200℃. In the coarse-grained Al-Mg-Sc-Sc alloys, the β" precipitation within the grain interior and also the precipitation hardening were highly dependent on the Mg/Si ratio,while the electrical conductivity was slightly affected by the Mg/Si ratio. A promoted β" precipitation was found in the case of Si excess(Mg/Si ratio <1.73), much greater than in the case of Mg excess(Mg/Si ratio>1.73). While in the ultrafine-grained Al-Mg-Si-Sc alloys, the electrical conductivity rather than the hardness was more sensitive to the Mg/Si ratio. The alloy with Si excess displayed electrical conductivity much higher than its counterpart with Mg excess. This is rationalized by the grain boundary precipitation promoted by Si, which reduced the solute atoms and precipitates within the grain interior. Age softening was found in the ultrafine-grained alloy with Si excess, but the ultrafine-grained alloy with Mg excess held the hardness almost unchanged during the aging. The hardness-conductivity correlation is comprehensively discussed by considering the coupling effect of Mg/Si ratio and grain size. A strategy to simultaneously increase the hardness/strength and electrical conductivity is proposed for the Al-Mg-SiSc alloys, based on present understanding of the predominant factors on strengthening and conductivity,respectively.
基金The National Science and Technology Major Project(No.2017ZX05009-003)the National Key Research and Development Program of China(No.2017YFC0307604)the Talent Foundation of China University of Petroleum(No.Y1215042)。
文摘A size-dependent continuum-based model is developed for the functionally graded(FG)Timoshenko micro-beams with viscoelastic properties,in which material parameters vary according to the power law along its axial direction.The size effect is incorporated by employing the modified couple stress theory and Kelvin-Voigt viscoelastic model,so that viscous components are included in the stress and the deviatoric segments of the symmetric couple stress tensors.The components of strain,curvature,stress and couple stress are formulated by combining them with the Timoshenko beam theory.Based on the Hamilton principle,the governing differential equations and boundary conditions for the micro-beam are expressed with arbitrary beam section shape and arbitrary type of loads.The size effect,FG effect,Poisson effect,and the influence of the beam section shape on the mechanical behaviors of viscoelastic FG micro-beams are investigated by taking the simply supported micro-beam subjected to point load as an example.Results show that the size effect on deflection,normal stress and couple stress are obvious when the size of the micro-beam is small enough,and the FG effects are obvious when the size of the micro-beam is large enough.Moreover,the Poisson ratio influences the size effect significantly and the beam section shape is also an important factor influencing the mechanical behavior of the micro-beam.
基金supported by the China Postdoctoral Science Foundation (No.2023M733712)the National Natural Science Foundation of China (No.31971491)。
文摘Tree mortality significantly influences forest structure and function,yet our understanding of its dynamic patterns among a range of tree sizes and among different plant functional types(PFTs)remains incomplete.This study analysed size-dependent tree mortality in a temperate forest,encompassing 46 tree species and 32,565 individuals across different PFTs(i.e.,evergreen conifer vs.deciduous broadleaf species,shade-tolerant vs.shade-intolerant species).By employing all-subset regression procedures and logistic generalized linear mixed-effects models,we identified distinct mortality patterns influenced by biotic and abiotic factors.Our results showed a stable mortality patte rn in eve rgreen conifer species,contrasted by a declining pattern in deciduous broadleaf and shadetolerant,as well as shade-intolerant species,across size classes.The contribution to tree mortality of evergreen conifer species shifted from abiotic to biotic factors with increasing size,while the mortality of deciduous broadleaf species was mainly influenced by biotic factors,such as initial diameter at breast height(DBH)and conspecific negative density.For shade-tolerant species,the mortality of small individuals was mainly determined by initial DBH and conspecific negative density dependence,whereas the mortality of large individuals was subjected to the combined effect of biotic(competition from neighbours)and abiotic factors(i.e.,convexity and pH).As for shade-intolerant species,competition from neighbours was found to be the main driver of tree mortality throughout their growth stages.Thus,these insights enhance our understanding of forest dynamics by revealing the size-dependent and PFT-specific tree mortality patterns,which may inform strategies for maintaining forest diversity and resilience in temperate forest ecosystems.
基金the State Key Development Program for Basic Research of China(Grant No.2017YFA0304300)the Key-Area Research and Development Program of Guangdong Province,China(Grant No.2020B0303030001)+1 种基金the National Natural Science Foundation of China(Grant No.T2121001)the Strategic Priority Research Program of Chinese Academy of Sciences(Grant No.XDB28000000).
文摘The non-Hermitian systems with the non-Hermitian skin effect(NHSE)are very sensitive to the imposed boundary conditions and lattice sizes,which lead to size-dependent non-Hermitian skin effects.Here,we report the experimental observation of NHSE with different boundary conditions and different lattice sizes in the unidirectional hopping model based on a circuit platform.The circuit admittance spectra and corresponding eigenstates are very sensitive to the presence of the boundary.Meanwhile,our experimental results show how the lattice sizes and boundary terms together affect the strength of NHSE.Therefore,our electric circuit provides a good platform to observe size-dependent boundary effects in non-Hermitian systems.
基金supported by the National Natural Science Foundation of China (Grant Nos.51722104,51625103,51790482,and 51761135031)the National Key Research and Development Program of China (2017YFA0700701)+3 种基金the 111 Project 2.0 of China(BP2018008)the Fok Ying-Tong Education Foundation (161096)the Fundamental Research Funds for the Central Universitiessupported by the Fundamental Research Funds for the Central Universities (xzy022019071)。
文摘Metastable high entropy alloys(HEAs) and amorphous metallic glasses(MGs), with the chemical disordered character, are intensively studied due to their excellent performance. Here, we introduce Cu to separately constrain these two metastable materials and comparatively investigate their deformation behaviors and mechanical properties of Cu/HEA Fe Co Cr Ni and Cu/MG Cu Zr nanolaminated micropillars in terms of intrinsic layer thickness h and extrinsic pillar diameter D. The metastable HEA layers, as the hard phase in Cu/HEA micropillars, are stable and dominate the deformation, while transformation(crystallization) occurs in MG which plays a minor role in deformation of Cu/MG micropillars. The h-controlled deformation mode transits from the D-independent homogenous-like deformation at large h to the Ddependent shear banding at small h in both Cu/HEA and Cu/MG micropillars. Although both Cu/HEA and Cu/MG micropillars exhibit a maximum strain hardening capability controlled by h, the former manifests much lower hardening capability compared with the latter. The intrinsic size h and extrinsic size D have a strong coupling effect on the strength of Cu/HEA and Cu/MG micropillars. The strength of strength of Cu/HEA micropillars exhibits the D-dependent transition from "smaller is stronger" to "smaller is weaker"with increasing h. By contrast, the strength of Cu/MG micropillars exhibits the transition from bulk-like D-independent behavior at large h to small volume D-dependent behavior(smaller is stronger) at small h.
基金financial support from the National Natural Science Foundation of China (NSFC-21776251, 21625604, 21671172 and 91934302)。
文摘Electrochemical ozone production(EOP) via water electrolysis represents an attractive method for the generation of high-purity O3. Herein, the X-PtZn/Zn-N-C electrocatalysts show a strong structural sensitive behavior depends on the size of the PtZn nanoparticles and their EOP activity exhibits a volcano-type dependence for the O3 performance in neutral media. The 7.7-PtZn/Zn-N-C exhibits EOP current efficiency of 4.2%, and shows the prominent performance in the production of gaseous O3 with a value of 1647 ppb at 30 min, which is almost 4-fold compared to 2.2-Pt Zn/Zn-N-C. Based on the experiments and theoretical calculations, the performance of the EOP process was determined by the nanoparticle size-effect and the synergistic effect between the PtZn nanoparticles and atomically dispersed Zn-N-C. Furthermore, the fivemembered cyclic structure of O3 can be stabilized between the PtZn nanoparticle and the Zn-N-C support,indicating that O3 is produced at the interface.
基金financial support from the National Natural Science Foundation of China(11472242,11672264,and 11621062)the Zhejiang Provincial Natural Science Foundation(LZ17A020001)the Fundamental Research Funds for the Central Universities
文摘Piezoelectric superlattice is a potential component for nanoelectromechanical systems. Due to the strong nonlocal effect such as flexoelectric effect at interfaces, classical piezoelectric theory is unable to accurately describe the electromechanical response of piezoelectric superlattice at nanoscale scale. Based on the previous nonlocal thermodynamics theory with flexoelectric effect Liu et al. （2016）, the size- dependent electromechanical properties of piezoelectric superlattices made of BaTiO3 （BTO） and PbTiO3 （PRO） layers are investigated systematically in the present work. Giant strain gradient is found near the interface between BTO and PTO layers, which leads to the significant enhancement of polarization in the superlattice due to the flexoelectric effect. For the piezoelectric BTO-PTO superlattices with different unit- cell sizes, the thickness of interface with nontrivial strain gradient is almost constant. The influence of strain gradient at the interface becomes significant when the size of superlattice decreases, As a result, a strong size dependence of electromechanical properties is predicted for the piezoelectric BTO-PTO superlattices, In particular, for the superlattices with a specific thickness ratio of BTO and PTO layers, the piezoelectric response can be several times larger than that of bulk structure. The present work demonstrates a practical wast to design the piezoelectric superlattices with high piezoelectric coefficient by using the nonlocal effect at nanoscale.
基金support of the National Natural Science Foundation of China(Grant Nos.52192611,51872031,61904013,and 62405157)China Postdoctoral Science Foundation(Nos.2023M741890 and GZC20231215)the Fundamental Research Funds for the Central Universities.
文摘The flexoelectric effect refers to the electromechanical coupling between electric polarization and mechanical strain gradient.It universally exists in a variety of materials in any space group,such as liquid crystals,dielectrics,biological materials,and semiconductors.Because of its unique size effect,nanoscale flexoelectricity has shown novel phenomena and promising applications in electronics,optronics,mechatronics,and photovoltaics.In this review,we provide a succinct report on the discovery and development of the flexoelectric effect,focusing on flexoelectric materials and related applications.Finally,we discuss recent flexoelectric research progress and still‐unsolved problems.
文摘Agricultural intensification has led to an increase in monoculture and the use of chemical pesticides,resulting in a decline in biodiversity and a reduction in ecosystem services,particularly biological pest management.However,studies have shown that agroforestry can not only improve land productivity and biodiversity but also regulate some ecosystem services.This study reviews the impacts of physical and biological factors on herbivorous pests,parasites,and predatory natural enemies in fruit-crop agroforestry systems.Fruit-crop agroforestry systems provide high spatial heterogeneity by altering crop layouts,regulating the microclimate and soil quality,and offering food resources and shelter for natural enemies,thus promoting biological pest control.This enhances biological control and makes the agrocomplex system an effective tool for sustainable agriculture.Our research shows that volatile plant substances attract or repel pests and natural enemies based on the characteristics of the insects themselves.When scientifically designed,fruit-crop agroforestry systems provide high spatial heterogeneity and favorable microclimatic conditions,which enhance biological pest control and make the agroforestry system an effective tool for sustainable agriculture.Our research shows that fruit-crop agroforestry systems can provide richer food resources and habitat,enhancing biological pest control and improving pest management.
基金the financial support from Henan Province Natural Science Foundation(No.252300420583)Henan Provincial Science and Technology Research Project(Nos.242102310455,242102310473,242102310517)the Key Project of Science and Technology Research funded by the Henan Provincial Department of Education(No.24A350002)。
文摘Liver cancer is the fourth cause of cancer-related deaths and the primary cause of death in patients with compensated cirrhosis.In recent years,the role of traditional Chinese medicine in the treatment of liver cancer has attracted more and more attention and recognition.Luteolin(LUT)and glycyrrhetinic(GA)are natural compounds extracted from Chinese herbal medicine.LUT exhibits various biological activity including anti-inflammatory,antibacterial,antiviral,anti-tumor,and neuroprotective effects.GA significantly inhibits the growth and metastasis of cancer cells.However,the low water solubility of both compounds hinders their clinical applications.In this study,rod-shaped nanoparticles(NPs)self-assembled from LUT and GA were designed to enhance drug solubility and tumor-targeting capability.We verified that the assembly mechanism of the NPs was π-π stacking.These NPs significantly inhibited the proliferation of liver cancer cells while had no significant effect on normal liver cells.In a mouse model of liver cancer,these NPs demonstrated superior tumor-targeting ability due to the enhanced permeability and retention effect,and the affinity of GA for liver cancer cells,resulting in better therapeutic efficacy with lower systemic toxicity.Results of network pharmacology analysis showed that LUT and GA respectively targeted estrogen receptor 1(ESR1)protein and cyclin-dependent kinase 1(CDK1)protein to corporately induce tumor cell cycle arrest,which induced the inhibition of tumor cell proliferation.In conclusion,this study provides a novel reference for the treatment of liver cancer.
