Current spatio-temporal action detection methods lack sufficient capabilities in extracting and comprehending spatio-temporal information. This paper introduces an end-to-end Adaptive Cross-Scale Fusion Encoder-Decode...Current spatio-temporal action detection methods lack sufficient capabilities in extracting and comprehending spatio-temporal information. This paper introduces an end-to-end Adaptive Cross-Scale Fusion Encoder-Decoder (ACSF-ED) network to predict the action and locate the object efficiently. In the Adaptive Cross-Scale Fusion Spatio-Temporal Encoder (ACSF ST-Encoder), the Asymptotic Cross-scale Feature-fusion Module (ACCFM) is designed to address the issue of information degradation caused by the propagation of high-level semantic information, thereby extracting high-quality multi-scale features to provide superior features for subsequent spatio-temporal information modeling. Within the Shared-Head Decoder structure, a shared classification and regression detection head is constructed. A multi-constraint loss function composed of one-to-one, one-to-many, and contrastive denoising losses is designed to address the problem of insufficient constraint force in predicting results with traditional methods. This loss function enhances the accuracy of model classification predictions and improves the proximity of regression position predictions to ground truth objects. The proposed method model is evaluated on the popular dataset UCF101-24 and JHMDB-21. Experimental results demonstrate that the proposed method achieves an accuracy of 81.52% on the Frame-mAP metric, surpassing current existing methods.展开更多
In tissue engineering(TE),tissue-inducing scaffolds are a promising solution for organ and tissue repair owing to their ability to attract stem cells in vivo,thereby inducing endogenous tissue regeneration through top...In tissue engineering(TE),tissue-inducing scaffolds are a promising solution for organ and tissue repair owing to their ability to attract stem cells in vivo,thereby inducing endogenous tissue regeneration through topological cues.An ideal TE scaffold should possess biomimetic cross-scale structures,similar to that of natural extracellular matrices,at the nano-to macro-scale level.Although freeform fabrication of TE scaffolds can be achieved through 3D printing,this method is limited in simultaneously building multiscale structures.To address this challenge,low-temperature fields were adopted in the traditional fabrication processes,such as casting and 3D printing.Ice crystals grow during scaffold fabrication and act as a template to control the nano-and micro-structures.These microstructures can be optimized by adjusting various parameters,such as the direction and magnitude of the low-temperature field.By preserving the macro-features fabricated using traditional methods,additional micro-structures with smaller scales can be incorporated simultaneously,realizing cross-scale structures that provide a better mimic of natural organs and tissues.In this paper,we present a state-of-the-art review of three low-temperature-field-assisted fabrication methods—freeze casting,cryogenic3D printing,and freeze spinning.Fundamental working principles,fabrication setups,processes,and examples of biomedical applications are introduced.The challenges and outlook for low-temperature-assisted fabrication are also discussed.展开更多
Global and local modeling is essential for image super-resolution tasks.However,current efforts often lack explicit consideration of the cross-scale knowledge in large-scale earth observation scenarios,resulting in su...Global and local modeling is essential for image super-resolution tasks.However,current efforts often lack explicit consideration of the cross-scale knowledge in large-scale earth observation scenarios,resulting in suboptimal single-scale representations in global and local modeling.The key motivation of this work is inspired by two observations:1)There exists hierarchical features at the local and global regions in remote sensing images,and 2)they exhibit scale variation of similar ground objects(e.g.cross-scale similarity).In light of these,this paper presents an effective method to grasp the global and local image hierarchies by systematically exploring the cross-scale correlation.Specifically,we developed a Cross-scale Self-Attention(CSA)to model the global features,which introduces an auxiliary token space to calculate cross-scale self-attention matrices,thus exploring global dependency from diverse token scales.To extract the cross-scale localities,a Cross-scale Channel Attention(CCA)is devised,where multi-scale features are explored and progressively incorporated into an enriched feature.Moreover,by hierarchically deploying CSA and CCA into transformer groups,the proposed Cross-scale Hierarchical Transformer(CHT)can effectively explore cross-scale representations in remote sensing images,leading to a favorable reconstruction performance.Comprehensive experiments and analysis on four remote sensing datasets have demonstrated the superiority of CHT in both simulated and real-world remote sensing scenes.In particular,our CHT outperforms the state-of-the-art approach(TransENet)in terms of PSNR by 0.11 dB on average,but only accounts for 54.8%of its parameters.展开更多
This paper analyzed the pore structure, quantified the pore fractal dimension, calculated the grading index(GI) of mixed aggregate, and studied the relationship among GI, pore structure, and strength to describe the c...This paper analyzed the pore structure, quantified the pore fractal dimension, calculated the grading index(GI) of mixed aggregate, and studied the relationship among GI, pore structure, and strength to describe the cross-scale characteristics of backfill, which is made from stone powder and cemented tailing. A series of experiments were conducted on stone powder cement tailings backfill(SPCTB). The GI formulas for mixed aggregates, containing stone powder and tailings, were derived based on the Füller theory. The nuclear magnetic resonance(NMR) fractal dimensions of backfills were derived using fractal geometry principles. Compared to the mesopore and macropore fractal dimensions, the correlation between micropore fractal dimension and macro-properties in terms of NMR porosity, pore structure complexity, uniaxial compression strength(UCS), and GI is the most significant. Macropore fractal dimension is generally correlated with UCS and GI and the other properties such as the shape of mixed aggregates also have an impact on fractal dimension. However, mesopore fractal dimension has no obvious relationship with macro-properties. Finally, the relationship between GI and UCS was studied, which contributed to improving backfill’s strength and optimizing gradation.展开更多
A simultaneous prediction of macroscopic deformation and microstructure evolution is critical for un-derstanding the deformation mechanism of components.In this work,the hydro-bulging process of 2219 aluminum alloy sh...A simultaneous prediction of macroscopic deformation and microstructure evolution is critical for un-derstanding the deformation mechanism of components.In this work,the hydro-bulging process of 2219 aluminum alloy sheet was investigated using cross-scale numerical modeling,in which the macroscopic finite element method(FEM)and crystal plasticity finite element method(CPFEM)were combined.The calculated texture evolution exhibits good agreement with the experimental results,and the stress er-ror between the two scales is generally small.The effects of different strain states on texture evolution and slip mode are further discussed.As the strain ratioηincreases,the volume fractions of the initial Rotated Copper texture component andγ-Fiber texture component decrease significantly,which tend to be stabilized at P texture component.The initial Rotated Cube texture component is inclined to rotate towards the Cube texture component,while the volume fraction of this orientation is relatively stable.The lower strain ratio can considerably enhance the activity of more equivalent slip systems,promoting a more uniform strain distribution over grains.The difficulty of grain deformation changes as the lat-tice rotates.The grain with easy-to-deform orientation can gradually rotate to a stable orientation during plastic deformation,which has a lower Schmid factor.展开更多
In order to further study the reliability of macro evaluation indexes,molecular dynamics (MD) was applied to the evaluation of asphalt binder.Micro evaluation indexes (potential energy,surface free energy,solubility p...In order to further study the reliability of macro evaluation indexes,molecular dynamics (MD) was applied to the evaluation of asphalt binder.Micro evaluation indexes (potential energy,surface free energy,solubility parameter and diffusion coefficient) of asphalt binder in different service phases (virgin,modified,aged and rejuvenated) were simulated.Combined with the variation characteristics of asphalt binder macro evaluation indexes (permeability,ductility,viscosity and softening point) in different service phases,the cross-scale correlation of macro-micro evaluation indexes was explored.The results show that the macro and micro evaluation indexes of asphalt binder have different characteristics in different service phases.The essence of the variation in the properties of asphalt binders is the difference in micro composition.In addition,there is a certain correlation between macro and micro evaluation indexes,which can be described by the gray relation theory.The cross-scale correlation of macro-micro evaluation indexes can provide a certain theoretical basis for the development of asphalt binder.展开更多
The urban morphological system,developed over multiple phases,exhibits complex cross-scale characteristics,with significant scale disc repancies among morphological elements at the same hierarchical level,which sugges...The urban morphological system,developed over multiple phases,exhibits complex cross-scale characteristics,with significant scale disc repancies among morphological elements at the same hierarchical level,which suggests that the cross-scale sliding model holds the potential to reveal additional characteristics of urban morphology.This paper introduces a multifractal method that integrates Spacematrix morphological classification for the analysis of detailed urban building data within defined boundaries.Using the Nanjing Old City in China as a case study,the results reveal a dense yet balanced urban form,showing annular differentiation characterized by fragmented fringe belts at the macro level and a uniform mixture of diverse land use types and building types at the micro level.The typical scale invariance and multifractality are not consistently observed across single-type analyses.The study identifies height uniformization and spaciousness differentiation in the scaling of urban morphology,attributing the multifractal mechanism to the interweaving and transformation of multiple types across scales.This enhanced multifractal approach improves spatial mapping capabilities,aiding in the elucidation of the formation mechanisms of urban morphology.展开更多
Flexoelectricity,an electromechanical coupling between strain gradient and electrical polarization in dielectrics or semiconductors,has attracted significant scientific interest.It is reported that large flexoelectric...Flexoelectricity,an electromechanical coupling between strain gradient and electrical polarization in dielectrics or semiconductors,has attracted significant scientific interest.It is reported that large flexoelectric behaviors can be obtained at the nanoscale because of the size effect.However,the flexoelectric responses of centrosymmetric semiconductors(CSs)are extremely weak under a conventional beam-bending approach,owing to weak flexoelectric coefficients and small strain gradients.The flexoelectric-like effect is an enhanced electromechanical effect coupling the flexoelectricity and piezoelectricity.In this paper,a composite structure consisting of piezoelectric dielectric layers and a CS layer is proposed.The electromechanical response of the CS is significantly enhanced via antisymmetric piezoelectric polarization.Consequently,the cross-scale mechanically tuned carrier distribution in the semiconductor is realized.Meanwhile,the significant size dependence of the electromechanical fields in the semiconductor is demonstrated.The flexoelectronics suppression is found when the semiconductor thickness reaches a critical size(0.8μm).In addition,the first-order carrier density of the composite structure under local loads is illustrated.Our results can suggest the structural design for flexoelectric semiconductor devices.展开更多
Transition metal carbide/nitride cores within MXenes make them considerably useful for ultra-high-temperature reinforcement.However,extensive research on Ti_(3)C_(2)T_(x)MXene has revealed its tendency to undergo a ph...Transition metal carbide/nitride cores within MXenes make them considerably useful for ultra-high-temperature reinforcement.However,extensive research on Ti_(3)C_(2)T_(x)MXene has revealed its tendency to undergo a phase transition to TiCy at temperatures above 800℃due to high activity of a superficial Ti atomic layer.Herein,spark plasma sintering of Ti_(3)C_(2)T_(x)and TiC is performed to prevent the Ti_(3)C_(2)T_(x)phase transition at temperatures up to 1900℃through the fabrication of composites at a pressure of 50 MPa.Using a focused ion beam scanning electron microscope to separate layered substances in the composites and examining selected area diffraction spots in a transmission electron microscope enabled identification of non-phase-transitioned MXene.First-principles calculations based on density functional theory indicated the formation of strong chemical bonding interfaces between Ti_(3)C_(2)T_(x)and TiC,which imposed a stability constraint on the Ti atomic layer at the Ti_(3)C_(2)T_(x)surface.Mechanical performance tests,such as three-point bending and fracture toughness analysis,demonstrated that the addition of Ti_(3)C_(2)T_(x)can effectively improve the cross-scale strengthening and toughening of the TiC matrix,providing a new path for designing and developing two-dimensional(2D)carbides cross-scale-enhanced three-dimensional(3D)carbides with the same elements relying on a wide variety of MXenes.展开更多
Mechanical softening behaviors of shale in CO_(2)-water–rock interaction are critical for shale gas exploitation and CO_(2)sequestration.This work investigated the cross-scale mechanical softening of shale triggered ...Mechanical softening behaviors of shale in CO_(2)-water–rock interaction are critical for shale gas exploitation and CO_(2)sequestration.This work investigated the cross-scale mechanical softening of shale triggered by CO_(2)-water–rock interaction.Initially,the mechanical softening of shale following 30 d of exposure to CO_(2)and water was assessed at the rock-forming mineral scale using nanoindentation.The mechanical alterations of rock-forming minerals,including quartz,muscovite,chlorite,and kaolinite,were analyzed and compared.Subsequently,an accurate grain-based modeling(AGBM)was proposed to upscale the nanoindentation results.Numerical models were generated based on the real microstructure of shale derived from TESCAN integrated minerals analyzer(TIMA)digital images.Mechanical parameters of shale minerals determined by nanoindentation served as input material properties for AGBMs.Finally,numerical simulations of uniaxial compression tests were conducted to investigate the impact of mineral softening on the macroscopic Young’s modulus and uniaxial compressive strength(UCS)of shale.The results present direct evidence of shale mineral softening during CO_(2)-water–rock interaction and explore its influence on the upscale mechanical properties of shale.This paper offers a microscopic perspective for comprehending CO_(2)-water-shale interactions and contributes to the development of a cross-scale mechanical model for shale.展开更多
Piezoelectric robots play important roles in the field of micromanipulation, but it is difficult for them to generate steady precision motion at any moment. In order to eliminate the changing inertial force and improv...Piezoelectric robots play important roles in the field of micromanipulation, but it is difficult for them to generate steady precision motion at any moment. In order to eliminate the changing inertial force and improve the motion smoothness, this work proposes a piezoelectric robot with continuous walking gait inspired by ants. The idea is verified with theoretical models and numerical simulation, and the performances are evaluated with experiments. The robot is proven to have the ability to generate 3-DOF(dgeree of freedom) continuous smooth motions with constant speeds. The maximum and minimum smooth velocities have a difference of six orders of magnitude, realizing cross-scale velocity control. Besides, the motion resolution reaches several nanometers with the unlimited workspace, so the cross-scale displacement control can be also obtained. Furthermore, with great robustness against varying loads, the stable actuation capability of the robot is more than 22 times of the self-weight. To sum up,the proposed robot generates cross-scale smooth motion in both aspects of displacement and velocity, so it has good prospects in the applications requiring steady precision motion. The design philosophy and research methods in this work can be valuable references for further advances of micromanipulation robots.展开更多
To predict global climate change and to implement the Kyoto Protocol for stabilizing atmospheric greenhouse gases concentrations require quantifying spatio-temporal variations in the terrestrial carbon sink accurately...To predict global climate change and to implement the Kyoto Protocol for stabilizing atmospheric greenhouse gases concentrations require quantifying spatio-temporal variations in the terrestrial carbon sink accurately. During the past decade multi-scale ecological experiment and observation networks have been established using various new technologies (e.g. controlled environmental facilities, eddy covariance techniques and quantitative remote sensing), and have obtained a large amount of data about terrestrial ecosystem carbon cycle. However, uncertainties in the magnitude and spatio-temporal variations of the terrestrial carbon sink and in understanding the underlying mechanisms have not been reduced significantly. One of the major reasons is that the observations and experiments were conducted at individual scales independently, but it is the interactions of factors and processes at different scales that determine the dynamics of the terrestrial carbon sink. Since experiments and observations are always conducted at specific scales, to understand cross-scale interactions requires mechanistic analysis that is best to be achieved by mechanistic modeling. However, mechanistic ecosystem models are mainly based on data from single-scale experiments and observations and hence have no capacity to simulate mechanistic cross-scale interconnection and interactions of ecosystem processes. New-generation mechanistic ecosystem models based on new ecological theoretical framework are needed to quantify the mechanisms from micro-level fast eco-physiological responses to macro-level slow acclimation in the pattern and structure in disturbed ecosystems. Multi-scale data-model fusion is a recently emerging approach to assimilate multi-scale observational data into mechanistic, dynamic modeling, in which the structure and parameters of mechanistic models for simulating cross-scale interactions are optimized using multi-scale observational data. The models are validated and evaluated at different spatial and temporal scales and real-time observational data are assimilated continuously into dynamic modeling for predicting and forecasting ecosystem changes realistically. in summary, a breakthrough in terrestrial carbon sink research requires using approaches of multi-scale observations and cross-scale modeling to understand and quantify interconnections and interactions among ecosystem processes at different scales and their controls over ecosystem carbon cycle.展开更多
The digital twin shop-floor has received much attention from the manufacturing industry as it is an important way to upgrade the shop-floor digitally and intelligently.As a key part of the shop-floor,humans'high a...The digital twin shop-floor has received much attention from the manufacturing industry as it is an important way to upgrade the shop-floor digitally and intelligently.As a key part of the shop-floor,humans'high autonomy and uncertainty leads to the difficulty in digital twin modeling of human behavior.Therefore,the modeling system for cross-scale human behavior in digital twin shop-floors was developed,powered by the data fusion of macro-behavior and micro-behavior virtual models.Shop-floor human macro-behavior mainly refers to the role of the human and their real-time position.Shop-floor micro-behavior mainly refers to real-time human limb posture and production behavior at their workstation.In this study,we reviewed and summarized a set of theoretical systems for cross-scale human behavior modeling in digital twin shop-floors.Based on this theoretical system,we then reviewed modeling theory and technology from macro-behavior and micro-behavior aspects to analyze the research status of shop-floor human behavior modeling.Lastly,we discuss and offer opinion on the application of cross-scale human behavior modeling in digital twin shop-floors.Cross-scale human behavior modeling is the key for realizing closed-loop interactive drive of human behavior in digital twin shop-floors.展开更多
基金support for this work was supported by Key Lab of Intelligent and Green Flexographic Printing under Grant ZBKT202301.
文摘Current spatio-temporal action detection methods lack sufficient capabilities in extracting and comprehending spatio-temporal information. This paper introduces an end-to-end Adaptive Cross-Scale Fusion Encoder-Decoder (ACSF-ED) network to predict the action and locate the object efficiently. In the Adaptive Cross-Scale Fusion Spatio-Temporal Encoder (ACSF ST-Encoder), the Asymptotic Cross-scale Feature-fusion Module (ACCFM) is designed to address the issue of information degradation caused by the propagation of high-level semantic information, thereby extracting high-quality multi-scale features to provide superior features for subsequent spatio-temporal information modeling. Within the Shared-Head Decoder structure, a shared classification and regression detection head is constructed. A multi-constraint loss function composed of one-to-one, one-to-many, and contrastive denoising losses is designed to address the problem of insufficient constraint force in predicting results with traditional methods. This loss function enhances the accuracy of model classification predictions and improves the proximity of regression position predictions to ground truth objects. The proposed method model is evaluated on the popular dataset UCF101-24 and JHMDB-21. Experimental results demonstrate that the proposed method achieves an accuracy of 81.52% on the Frame-mAP metric, surpassing current existing methods.
基金National Natural Science Foundation Council of China(Grant No.52305359)Hubei Provincial Natural Science Foundation of China(Grant No.2023AFB141)National Medical Products Administration Key Laboratory for Dental Materials(PKUSS20240401)。
文摘In tissue engineering(TE),tissue-inducing scaffolds are a promising solution for organ and tissue repair owing to their ability to attract stem cells in vivo,thereby inducing endogenous tissue regeneration through topological cues.An ideal TE scaffold should possess biomimetic cross-scale structures,similar to that of natural extracellular matrices,at the nano-to macro-scale level.Although freeform fabrication of TE scaffolds can be achieved through 3D printing,this method is limited in simultaneously building multiscale structures.To address this challenge,low-temperature fields were adopted in the traditional fabrication processes,such as casting and 3D printing.Ice crystals grow during scaffold fabrication and act as a template to control the nano-and micro-structures.These microstructures can be optimized by adjusting various parameters,such as the direction and magnitude of the low-temperature field.By preserving the macro-features fabricated using traditional methods,additional micro-structures with smaller scales can be incorporated simultaneously,realizing cross-scale structures that provide a better mimic of natural organs and tissues.In this paper,we present a state-of-the-art review of three low-temperature-field-assisted fabrication methods—freeze casting,cryogenic3D printing,and freeze spinning.Fundamental working principles,fabrication setups,processes,and examples of biomedical applications are introduced.The challenges and outlook for low-temperature-assisted fabrication are also discussed.
基金supported in part by the National Natural Science Foundation of China[grant numbers 42230108,and 61971319].
文摘Global and local modeling is essential for image super-resolution tasks.However,current efforts often lack explicit consideration of the cross-scale knowledge in large-scale earth observation scenarios,resulting in suboptimal single-scale representations in global and local modeling.The key motivation of this work is inspired by two observations:1)There exists hierarchical features at the local and global regions in remote sensing images,and 2)they exhibit scale variation of similar ground objects(e.g.cross-scale similarity).In light of these,this paper presents an effective method to grasp the global and local image hierarchies by systematically exploring the cross-scale correlation.Specifically,we developed a Cross-scale Self-Attention(CSA)to model the global features,which introduces an auxiliary token space to calculate cross-scale self-attention matrices,thus exploring global dependency from diverse token scales.To extract the cross-scale localities,a Cross-scale Channel Attention(CCA)is devised,where multi-scale features are explored and progressively incorporated into an enriched feature.Moreover,by hierarchically deploying CSA and CCA into transformer groups,the proposed Cross-scale Hierarchical Transformer(CHT)can effectively explore cross-scale representations in remote sensing images,leading to a favorable reconstruction performance.Comprehensive experiments and analysis on four remote sensing datasets have demonstrated the superiority of CHT in both simulated and real-world remote sensing scenes.In particular,our CHT outperforms the state-of-the-art approach(TransENet)in terms of PSNR by 0.11 dB on average,but only accounts for 54.8%of its parameters.
基金Project(41672298)supported by the National Natural Science Foundation of ChinaProject(2017YFC0602901)supported by the National Key Research and Development Program of China。
文摘This paper analyzed the pore structure, quantified the pore fractal dimension, calculated the grading index(GI) of mixed aggregate, and studied the relationship among GI, pore structure, and strength to describe the cross-scale characteristics of backfill, which is made from stone powder and cemented tailing. A series of experiments were conducted on stone powder cement tailings backfill(SPCTB). The GI formulas for mixed aggregates, containing stone powder and tailings, were derived based on the Füller theory. The nuclear magnetic resonance(NMR) fractal dimensions of backfills were derived using fractal geometry principles. Compared to the mesopore and macropore fractal dimensions, the correlation between micropore fractal dimension and macro-properties in terms of NMR porosity, pore structure complexity, uniaxial compression strength(UCS), and GI is the most significant. Macropore fractal dimension is generally correlated with UCS and GI and the other properties such as the shape of mixed aggregates also have an impact on fractal dimension. However, mesopore fractal dimension has no obvious relationship with macro-properties. Finally, the relationship between GI and UCS was studied, which contributed to improving backfill’s strength and optimizing gradation.
基金financially supported by the National Natural Science Foundation of China(No.52275322)the Heilongjiang Touyan Team(No.HITTY-20190015).
文摘A simultaneous prediction of macroscopic deformation and microstructure evolution is critical for un-derstanding the deformation mechanism of components.In this work,the hydro-bulging process of 2219 aluminum alloy sheet was investigated using cross-scale numerical modeling,in which the macroscopic finite element method(FEM)and crystal plasticity finite element method(CPFEM)were combined.The calculated texture evolution exhibits good agreement with the experimental results,and the stress er-ror between the two scales is generally small.The effects of different strain states on texture evolution and slip mode are further discussed.As the strain ratioηincreases,the volume fractions of the initial Rotated Copper texture component andγ-Fiber texture component decrease significantly,which tend to be stabilized at P texture component.The initial Rotated Cube texture component is inclined to rotate towards the Cube texture component,while the volume fraction of this orientation is relatively stable.The lower strain ratio can considerably enhance the activity of more equivalent slip systems,promoting a more uniform strain distribution over grains.The difficulty of grain deformation changes as the lat-tice rotates.The grain with easy-to-deform orientation can gradually rotate to a stable orientation during plastic deformation,which has a lower Schmid factor.
基金Funded by the Fundamental Research Funds for the Central Universities (No. 2572021AW10)。
文摘In order to further study the reliability of macro evaluation indexes,molecular dynamics (MD) was applied to the evaluation of asphalt binder.Micro evaluation indexes (potential energy,surface free energy,solubility parameter and diffusion coefficient) of asphalt binder in different service phases (virgin,modified,aged and rejuvenated) were simulated.Combined with the variation characteristics of asphalt binder macro evaluation indexes (permeability,ductility,viscosity and softening point) in different service phases,the cross-scale correlation of macro-micro evaluation indexes was explored.The results show that the macro and micro evaluation indexes of asphalt binder have different characteristics in different service phases.The essence of the variation in the properties of asphalt binders is the difference in micro composition.In addition,there is a certain correlation between macro and micro evaluation indexes,which can be described by the gray relation theory.The cross-scale correlation of macro-micro evaluation indexes can provide a certain theoretical basis for the development of asphalt binder.
基金supported by Jiangsu Provincial Department of Science and Technology(Grant No.BE2023799)the National Natural Science Foundation of China(Grant No.52308051)。
文摘The urban morphological system,developed over multiple phases,exhibits complex cross-scale characteristics,with significant scale disc repancies among morphological elements at the same hierarchical level,which suggests that the cross-scale sliding model holds the potential to reveal additional characteristics of urban morphology.This paper introduces a multifractal method that integrates Spacematrix morphological classification for the analysis of detailed urban building data within defined boundaries.Using the Nanjing Old City in China as a case study,the results reveal a dense yet balanced urban form,showing annular differentiation characterized by fragmented fringe belts at the macro level and a uniform mixture of diverse land use types and building types at the micro level.The typical scale invariance and multifractality are not consistently observed across single-type analyses.The study identifies height uniformization and spaciousness differentiation in the scaling of urban morphology,attributing the multifractal mechanism to the interweaving and transformation of multiple types across scales.This enhanced multifractal approach improves spatial mapping capabilities,aiding in the elucidation of the formation mechanisms of urban morphology.
基金supported by the National Key Research and Development Program of China(Grant No.2021YFB2011400)the National Natural Science Foundation of China(Grant No.52375081).
文摘Flexoelectricity,an electromechanical coupling between strain gradient and electrical polarization in dielectrics or semiconductors,has attracted significant scientific interest.It is reported that large flexoelectric behaviors can be obtained at the nanoscale because of the size effect.However,the flexoelectric responses of centrosymmetric semiconductors(CSs)are extremely weak under a conventional beam-bending approach,owing to weak flexoelectric coefficients and small strain gradients.The flexoelectric-like effect is an enhanced electromechanical effect coupling the flexoelectricity and piezoelectricity.In this paper,a composite structure consisting of piezoelectric dielectric layers and a CS layer is proposed.The electromechanical response of the CS is significantly enhanced via antisymmetric piezoelectric polarization.Consequently,the cross-scale mechanically tuned carrier distribution in the semiconductor is realized.Meanwhile,the significant size dependence of the electromechanical fields in the semiconductor is demonstrated.The flexoelectronics suppression is found when the semiconductor thickness reaches a critical size(0.8μm).In addition,the first-order carrier density of the composite structure under local loads is illustrated.Our results can suggest the structural design for flexoelectric semiconductor devices.
基金the financial support from the National Natural Science Foundation of China(Grant Nos.11872171,91016014,and 51872062)Fundamental Research Funds for the Central Universities(Grant No.B200202117)。
文摘Transition metal carbide/nitride cores within MXenes make them considerably useful for ultra-high-temperature reinforcement.However,extensive research on Ti_(3)C_(2)T_(x)MXene has revealed its tendency to undergo a phase transition to TiCy at temperatures above 800℃due to high activity of a superficial Ti atomic layer.Herein,spark plasma sintering of Ti_(3)C_(2)T_(x)and TiC is performed to prevent the Ti_(3)C_(2)T_(x)phase transition at temperatures up to 1900℃through the fabrication of composites at a pressure of 50 MPa.Using a focused ion beam scanning electron microscope to separate layered substances in the composites and examining selected area diffraction spots in a transmission electron microscope enabled identification of non-phase-transitioned MXene.First-principles calculations based on density functional theory indicated the formation of strong chemical bonding interfaces between Ti_(3)C_(2)T_(x)and TiC,which imposed a stability constraint on the Ti atomic layer at the Ti_(3)C_(2)T_(x)surface.Mechanical performance tests,such as three-point bending and fracture toughness analysis,demonstrated that the addition of Ti_(3)C_(2)T_(x)can effectively improve the cross-scale strengthening and toughening of the TiC matrix,providing a new path for designing and developing two-dimensional(2D)carbides cross-scale-enhanced three-dimensional(3D)carbides with the same elements relying on a wide variety of MXenes.
基金supported by the China Postdoctoral Science Foundation(Grant Nos.2023TQ0247 and 2023M732715)the Postdoctoral Fellowship Program(Grade B)of China Postdoctoral Science Foundation(Grant No.GZB20230544)the National Natural Science Foundation of China(Grant Nos.U21A20153 and 41841018).
文摘Mechanical softening behaviors of shale in CO_(2)-water–rock interaction are critical for shale gas exploitation and CO_(2)sequestration.This work investigated the cross-scale mechanical softening of shale triggered by CO_(2)-water–rock interaction.Initially,the mechanical softening of shale following 30 d of exposure to CO_(2)and water was assessed at the rock-forming mineral scale using nanoindentation.The mechanical alterations of rock-forming minerals,including quartz,muscovite,chlorite,and kaolinite,were analyzed and compared.Subsequently,an accurate grain-based modeling(AGBM)was proposed to upscale the nanoindentation results.Numerical models were generated based on the real microstructure of shale derived from TESCAN integrated minerals analyzer(TIMA)digital images.Mechanical parameters of shale minerals determined by nanoindentation served as input material properties for AGBMs.Finally,numerical simulations of uniaxial compression tests were conducted to investigate the impact of mineral softening on the macroscopic Young’s modulus and uniaxial compressive strength(UCS)of shale.The results present direct evidence of shale mineral softening during CO_(2)-water–rock interaction and explore its influence on the upscale mechanical properties of shale.This paper offers a microscopic perspective for comprehending CO_(2)-water-shale interactions and contributes to the development of a cross-scale mechanical model for shale.
基金supported by the National Natural Science Foundation of China (Grant Nos. U1913215 and 51975144)。
文摘Piezoelectric robots play important roles in the field of micromanipulation, but it is difficult for them to generate steady precision motion at any moment. In order to eliminate the changing inertial force and improve the motion smoothness, this work proposes a piezoelectric robot with continuous walking gait inspired by ants. The idea is verified with theoretical models and numerical simulation, and the performances are evaluated with experiments. The robot is proven to have the ability to generate 3-DOF(dgeree of freedom) continuous smooth motions with constant speeds. The maximum and minimum smooth velocities have a difference of six orders of magnitude, realizing cross-scale velocity control. Besides, the motion resolution reaches several nanometers with the unlimited workspace, so the cross-scale displacement control can be also obtained. Furthermore, with great robustness against varying loads, the stable actuation capability of the robot is more than 22 times of the self-weight. To sum up,the proposed robot generates cross-scale smooth motion in both aspects of displacement and velocity, so it has good prospects in the applications requiring steady precision motion. The design philosophy and research methods in this work can be valuable references for further advances of micromanipulation robots.
基金This study was supported by the China's Ministry of Science and Technology(Grant No.G2002CB412507)the National Natural Science Foundation of China(Grant No.40425103).
文摘To predict global climate change and to implement the Kyoto Protocol for stabilizing atmospheric greenhouse gases concentrations require quantifying spatio-temporal variations in the terrestrial carbon sink accurately. During the past decade multi-scale ecological experiment and observation networks have been established using various new technologies (e.g. controlled environmental facilities, eddy covariance techniques and quantitative remote sensing), and have obtained a large amount of data about terrestrial ecosystem carbon cycle. However, uncertainties in the magnitude and spatio-temporal variations of the terrestrial carbon sink and in understanding the underlying mechanisms have not been reduced significantly. One of the major reasons is that the observations and experiments were conducted at individual scales independently, but it is the interactions of factors and processes at different scales that determine the dynamics of the terrestrial carbon sink. Since experiments and observations are always conducted at specific scales, to understand cross-scale interactions requires mechanistic analysis that is best to be achieved by mechanistic modeling. However, mechanistic ecosystem models are mainly based on data from single-scale experiments and observations and hence have no capacity to simulate mechanistic cross-scale interconnection and interactions of ecosystem processes. New-generation mechanistic ecosystem models based on new ecological theoretical framework are needed to quantify the mechanisms from micro-level fast eco-physiological responses to macro-level slow acclimation in the pattern and structure in disturbed ecosystems. Multi-scale data-model fusion is a recently emerging approach to assimilate multi-scale observational data into mechanistic, dynamic modeling, in which the structure and parameters of mechanistic models for simulating cross-scale interactions are optimized using multi-scale observational data. The models are validated and evaluated at different spatial and temporal scales and real-time observational data are assimilated continuously into dynamic modeling for predicting and forecasting ecosystem changes realistically. in summary, a breakthrough in terrestrial carbon sink research requires using approaches of multi-scale observations and cross-scale modeling to understand and quantify interconnections and interactions among ecosystem processes at different scales and their controls over ecosystem carbon cycle.
基金This work was supported by the National Key Research and Development Program,China[2020YFB1708400]the National Defense Fundamental Research Program,China[JCKY2020210B006,JCKY2017204B053].
文摘The digital twin shop-floor has received much attention from the manufacturing industry as it is an important way to upgrade the shop-floor digitally and intelligently.As a key part of the shop-floor,humans'high autonomy and uncertainty leads to the difficulty in digital twin modeling of human behavior.Therefore,the modeling system for cross-scale human behavior in digital twin shop-floors was developed,powered by the data fusion of macro-behavior and micro-behavior virtual models.Shop-floor human macro-behavior mainly refers to the role of the human and their real-time position.Shop-floor micro-behavior mainly refers to real-time human limb posture and production behavior at their workstation.In this study,we reviewed and summarized a set of theoretical systems for cross-scale human behavior modeling in digital twin shop-floors.Based on this theoretical system,we then reviewed modeling theory and technology from macro-behavior and micro-behavior aspects to analyze the research status of shop-floor human behavior modeling.Lastly,we discuss and offer opinion on the application of cross-scale human behavior modeling in digital twin shop-floors.Cross-scale human behavior modeling is the key for realizing closed-loop interactive drive of human behavior in digital twin shop-floors.
