Grain boundaries(GBs)play a crucial role on the structural stability and mechanical properties of Cu and its alloys.In this work,molecular dynamics(MD)simulations are employed to study the effects of Fe solutes on the...Grain boundaries(GBs)play a crucial role on the structural stability and mechanical properties of Cu and its alloys.In this work,molecular dynamics(MD)simulations are employed to study the effects of Fe solutes on the formation energy,excess volume,dislocations and melting behaviors of GBs in CuFe alloys.It is illustrated that Fe solute affects the structural stability of Cu GBs substantially,the formation energy of GBs is reduced,but the thickness and melting point of GBs are increased,that is,the structural stability of Cu GBs is significantly improved owing to the Fe solutes.A strong scaling law exists between the formation energy,excess volume,thickness and melting point of GBs.Therefore,Fe solid solute plays an important role in the characteristics of GBs in bi-crystal Cu.展开更多
The experimental results in previous studies have indicated that during the ductile fracture of pure metals,vacancies aggregate and form voids at grain boundaries.However,the physical mechanism underlying this phenome...The experimental results in previous studies have indicated that during the ductile fracture of pure metals,vacancies aggregate and form voids at grain boundaries.However,the physical mechanism underlying this phenomenon remains not fully understood.This study derives the equilibrium distribution of vacancies analytically by following thermodynamics and the micromechanics of crystal defects.This derivation suggests that vacancies cluster in regions under hydrostatic compression to minimize the elastic strain energy.Subsequently,a finite element model is developed for examining more general scenarios of interaction between vacancies and grain boundaries.This model is first verified and validated through comparison with some available analytical solutions,demonstrating consistency between finite element simulation results and analytical solutions within a specified numerical accuracy.A systematic numerical study is then conducted to investigate the mechanism that might govern the micromechanical interaction between grain boundaries and the profuse vacancies typically generated during plastic deformation.The simulation results indicate that the reduction in total elastic strain energy can indeed drive vacancies toward grain boundaries,potentially facilitating void nucleation in ductile fracture.展开更多
The frequent occurrence of extreme weather events has rendered numerous landslides to a global natural disaster issue.It is crucial to rapidly and accurately determine the boundaries of landslides for geohazards evalu...The frequent occurrence of extreme weather events has rendered numerous landslides to a global natural disaster issue.It is crucial to rapidly and accurately determine the boundaries of landslides for geohazards evaluation and emergency response.Therefore,the Skip Connection DeepLab neural network(SCDnn),a deep learning model based on 770 optical remote sensing images of landslide,is proposed to improve the accuracy of landslide boundary detection.The SCDnn model is optimized for the over-segmentation issue which occurs in conventional deep learning models when there is a significant degree of similarity between topographical geomorphic features.SCDnn exhibits notable improvements in landslide feature extraction and semantic segmentation by combining an enhanced Atrous Spatial Pyramid Convolutional Block(ASPC)with a coding structure that reduces model complexity.The experimental results demonstrate that SCDnn can identify landslide boundaries in 119 images with MIoU values between 0.8and 0.9;while 52 images with MIoU values exceeding 0.9,which exceeds the identification accuracy of existing techniques.This work can offer a novel technique for the automatic extensive identification of landslide boundaries in remote sensing images in addition to establishing the groundwork for future inve stigations and applications in related domains.展开更多
Spatial control of lithium deposition is the most important issue in lithium-metal batteries because of the considerable control of lithium dendrite suppression via the uniform distribution of Li^(+)flux.Although seed...Spatial control of lithium deposition is the most important issue in lithium-metal batteries because of the considerable control of lithium dendrite suppression via the uniform distribution of Li^(+)flux.Although seed materials are crucial for the behavior of lithium deposition,in-depth studies on their physical and chemical control have not been conducted.Here,we describe a new design of seed structure comprising a wrinkled Cu/graphene substrate surrounded by copper(Ⅰ)oxide(Cu_(2)O)on a graphene grain boundary over a large area,which is fabricated by the oxidation of the Cu surface via graphene boundary defects by using chemical vapor deposition(CVD).Scanning and transmission electron microscopy results reveal that Cu_(2)O on the graphene boundary can render a preferential reaction with lithium during the first deposition and assist in the uniform deposition of lithium by preventing the agglomeration of lithium clusters during the second deposition.This two-step process is attributed to the degree of selectivity due to the difference in lithium affinity,which allows long-term electrochemical stability and a high rate capability via boundary effects.This study highlights the significance of the boundary effect,which can open new avenues for the formation of a large family of seed structures in lithium-metal batteries.展开更多
Due to the insufficient slip systems in hexagonal close-packed structure,twinning is frequently activated to support stable plastic deformation of Mg alloy.In this work,we found four typical twin-like interfaces with ...Due to the insufficient slip systems in hexagonal close-packed structure,twinning is frequently activated to support stable plastic deformation of Mg alloy.In this work,we found four typical twin-like interfaces with misorientations of 102°,109°,142°and 149°,respectively,which had not only a shared[1120]zone axis of neighboring grains,but also overlapped diffraction spots similar to twins.However,highresolution transmission electron microscope(HRTEM)analysis revealed that the interfaces in real space deviated from the supposed twinning planes in reciprocal space,i.e.their overlapped diffraction spots.We clarified that the incoherent interfaces were co-axial grain boundaries(CGBs).Additionally,a special angle ofθ,close to 90°,between the interface and one side of basal plane,was frequently formed in CGBs.We proposed that interaction of multiple twinning contributes to the formation of CGBs,and theθis formed due to alternative tensile and compression twinning under a uniaxial loading.展开更多
In recent years, perovskite solar cells(PSCs) have propelled into the limelight owing to rapid development of efficiency;however, the abundant defects at the perovskite grain boundaries result in unwanted energy loss ...In recent years, perovskite solar cells(PSCs) have propelled into the limelight owing to rapid development of efficiency;however, the abundant defects at the perovskite grain boundaries result in unwanted energy loss and structural degradation. Here, the grain boundaries of perovskite polycrystalline films have been found to act as nanocapillaries for capturing perovskite quantum dots(PQDs), which enable the conformal assemble of PQDs at the top interspace between perovskite grains. The existence of PQDs passivated the surface defects, optimized the interfacial band alignments, and ultimately improved the power conversion efficiency from 19.27% to 22.47% in inverted PSCs. Our findings open up the possibility of selective assembly and structural modulation of the perovskite nanostructures towards efficient and stable PSCs.展开更多
LetΓbe a Jordan curve in the complex plane and let Γ_(λ) be the constant distance boundary ofΓ.Vellis and Wu[10]introduced the notion of a(ζ,r_(0))-chordal property which guarantees that,whenλis not too large, ...LetΓbe a Jordan curve in the complex plane and let Γ_(λ) be the constant distance boundary ofΓ.Vellis and Wu[10]introduced the notion of a(ζ,r_(0))-chordal property which guarantees that,whenλis not too large, Γ_(λ) is a Jordan curve whenζ=1/2 and Γ_(λ) is a quasicircle when 0<ζ<1/2.We introduce the(ζ,r_(0),t)-chordal property,which generalizes the(ζ,r_(0))-chordal property,and we show that under the condition thatΓis(ζ,r_(0),√t)-chordal with 0<ζ<r_(0)^(1−√t)/2,there existsε>0 such that Γ_(λ) is a t-quasicircle once Γ_(λ) is a Jordan curve when 0<λ<ε.In the last part of this paper,we provide an example:Γis a kind of Koch snowflake curve which does not have the(ζ,r_(0))-chordal property for any 0<ζ<1/2,however Γ_(λ) is a Jordan curve whenλis small enough.Meanwhile,Γhas the(ζ,r_(0),√t)-chordal property with 0<ζ<r_(0)^(1−√t)/2 for any t∈(0,1/4).As a corollary of our main theorem, Γ_(λ) is a t-quasicircle for all 0<t<1/4 whenλis small enough.This means that our(ζ,r_(0),t)-chordal property is more general and applicable to more complicated curves.展开更多
植物顶端分生组织可分为中央区,周缘区和肋区。在植物胚后发育中,侧生器官产生于顶端分生组织的周缘区。顶端分生组织和侧生器官之间的边界的建立和维持是一个非常重要的发育过程,许多调节子参与控制这个过程。拟南芥的 LATERALORGANBOU...植物顶端分生组织可分为中央区,周缘区和肋区。在植物胚后发育中,侧生器官产生于顶端分生组织的周缘区。顶端分生组织和侧生器官之间的边界的建立和维持是一个非常重要的发育过程,许多调节子参与控制这个过程。拟南芥的 LATERALORGANBOUNDARIES(LOB)基因具有独特的表达模式,其表达的范围与上述的边界区域重合。LOB基因隶属于一个大的基因家族——L O B 结构域基因家族。该家族编码的蛋白在 N 端具有一个保守的LOB结构域,该家族 LOB 基因以外的成员也参与拟南芥不同的发育过程。为了探讨在与拟南芥亲缘关系较远的豆科中 LOB 同源基因的功能,我们在豆科模式植物百脉根中分离了3 个 LOB 同源基因,命名为 LjLOB 基因,并用 RNA 原位杂交方法研究了这3个基因的表达模式。研究结果显示,L j L O B 1 和LjLOB3都强烈地在小叶原基的基部表达,这种表达模式可能与小叶原基和复叶原基之间的边界相关。而LjLOB4则在发育中的花芽不同轮之间的边界上表达。百脉根中这3 个基因具有不同的表达模式,强烈地提示它们的功能发生了分歧:L j L O B 1 和L j L O B 3 可能在复叶发育中具有重要功能;而LjLOB4 则可能参与了花的发育。展开更多
By means of surface mechanical attrition treatment ( SMAT), the groin size with a diameter of aboat 60hm formed at about 20μm depth and numerous mechanical twins at about 50μm depth from the treated surface were ...By means of surface mechanical attrition treatment ( SMAT), the groin size with a diameter of aboat 60hm formed at about 20μm depth and numerous mechanical twins at about 50μm depth from the treated surface were synthesized in 316L stainless steel because of the different distributions of strain and strain rate along depth orientation. For instance the maximum strain rate reached 10^3-10^4s^-1 on the top surface. The relationship between the microsturcture and the corrosion property was studied in 0.05M H2SO4+ 0.25M Na2SO4 aqueous solution, and the results show an extreme improvement of corrosion resistance owing to the appearance of twin boundaries and the obvious reduction in corrosion resistance attributed to the presence of nanocrystaline boundaries.展开更多
Just like in sedimentary stratigraphy, the factor for constructing volcanostratigraphic volcanostratigraphic boundary is an important framework. The fundamental factor of volcanostratigraphic boundaries is to classify...Just like in sedimentary stratigraphy, the factor for constructing volcanostratigraphic volcanostratigraphic boundary is an important framework. The fundamental factor of volcanostratigraphic boundaries is to classify the types and define their characteristics. Based on field investigation and cross-wells section analysis of Mesozoic volcanostratigraphy in NE China, 5 types of volcanostratigraphic boundaries have been recognized, namely eruptive conformity boundary (ECB), eruptive unconformity boundary (EUB), eruptive interval unconformity boundary (EIUB), tectonic unconformity boundary (TUB) and intrusive contacts boundary (ICB). Except ICB, the unconformity boundaries can be divided into angular unconformity and paraconformity. The time spans and signs of these boundaries are analyzed by using age data of some volcanic fields that have been published. The time spans of ECB and EUB are from several minutes to years. In lava flows, cooling crust is distributed above and below ECB and EUB; in pyroclastic flows, airfalls and lahars, a fine layer below these boundaries has no discernable erosion at every part of the boundary. EUB may be curved or cross curved and jagged. The scale of ECB/EUB is dependent on the scale of lava flow or pyroclastic flows. The time span of EIUB is from decades to thousands of years. There is also weathered crust under EIUB and sedimentary rock beds overlie EIUB. In most instances, weathered crust and thin sedimentary beds are associated with each other laterally. The boundary is a smooth curved plane. The scale of EIUB is dependent on the scale of the volcano or volcano groups. The characteristics of TUB are similar to EIUB's. The time interval of TUB is from tens of thousands to millions of years. The scale of TUB depends on the scale of the basin or volcanic field. Both the lab data and logging data of wells in the Songliao Basin reveal that the porosity is greatly related to the boundaries in the lava flows. There is a high-porosity belt below ECB, EUB or EIUB, and the porosity decreases when it is apart from the boundary. The high-porosity belt below ECB and EUB is mainly contributed by primary porosity, such as vesicles. The high-porosity belt below EIUB is mainly contributed by primary and secondary porosity, such as association of vesicles and spongy pores, so the area near the boundary in lava flows is a very important target for reservoirs.展开更多
The behaviors of La and Ce on gram boundaries in carbon manganese clean steel were investigated by high-reso- lution transmission elecetron microscope (HRTEM), scanning elecetron microscopy(SEM ), energy dispersiv...The behaviors of La and Ce on gram boundaries in carbon manganese clean steel were investigated by high-reso- lution transmission elecetron microscope (HRTEM), scanning elecetron microscopy(SEM ), energy dispersive spectrometer (EDS) and X-ray diffraction(XRD) analysis. The existing forms of rare earths (RE) in clean steel were as follows: dissolved in sohd solution, forming inclusion or second phase containing RE (RE-Fe-P, La-P, Fe-La eutectic and Fe-Ce phase). The dissolved La or Ce segregated at grain boundaries. The segregation of both S and P at gram boundaries was reduced with suitable RE content. The impact toughness of the steel was improved obviously. La and Ce had effecets on purifying molten steel and modifying inclusions in clean steel, whereas with excessive La or Ce, La-Fe-P, La-P and Fe-La eutecetic phase or Ce-Fe-P and Fe-Ce intermetallic compound would form along grain boundaries, causing the impact energy to decrease significantly.展开更多
Almost all intraplate caprocks experienced strong deformation during the convergence of microplates, and then disintegrated into many secondary geologic units with the special characters, such as irregular boundaries ...Almost all intraplate caprocks experienced strong deformation during the convergence of microplates, and then disintegrated into many secondary geologic units with the special characters, such as irregular boundaries and particular structural assemblages. In order to understand the formation mechanism of these special phenomena, a rheological experiment on the structural scenery of the Tongling area is carried out. The result shows that the primary regular and uniform boundaries of the Tongling area becomes irregular because of the enclosing and confinement of surrounding geological units in the process of 'compression-shearing-rotation-drag'; simultaneously, two specific 'drag depressions' developed at two opposite corners of the block. The former and the later phenomena can be regarded as a typical regional-scale rheological effect and necessary outcome of intraplate deformation respectively.展开更多
The method of inputting the seismic wave determines the accuracy of the simulation of soil-structure dynamic interaction. The wave method is a commonly used approach for seismic wave input, which converts the incident...The method of inputting the seismic wave determines the accuracy of the simulation of soil-structure dynamic interaction. The wave method is a commonly used approach for seismic wave input, which converts the incident wave into equivalent loads on the cutoff boundaries. The wave method has high precision, but the implementation is complicated, especially for three-dimensional models. By deducing another form of equivalent input seismic loads in the fi nite element model, a new seismic wave input method is proposed. In the new method, by imposing the displacements of the free wave fi eld on the nodes of the substructure composed of elements that contain artifi cial boundaries, the equivalent input seismic loads are obtained through dynamic analysis of the substructure. Subsequently, the equivalent input seismic loads are imposed on the artifi cial boundary nodes to complete the seismic wave input and perform seismic analysis of the soil-structure dynamic interaction model. Compared with the wave method, the new method is simplifi ed by avoiding the complex processes of calculating the equivalent input seismic loads. The validity of the new method is verifi ed by the dynamic analysis numerical examples of the homogeneous and layered half space under vertical and oblique incident seismic waves.展开更多
This paper presents a method to generate unstructured adaptive meshes with moving boundaries and its application to CFD. Delaunay triangulation criterion in conjunction with the automatic point creation is used to gen...This paper presents a method to generate unstructured adaptive meshes with moving boundaries and its application to CFD. Delaunay triangulation criterion in conjunction with the automatic point creation is used to generate 2 D and 3 D unstructured grids. A local grid regeneration method is proposed to cope with moving boundaries. Numerical examples include the interactions of shock waves with movable bodies and the movement of a projectile within a ram accelerator, illustrating an efficient and robust mesh generation method developed.展开更多
The corrosion behavior of 5 wt%Cr steel tempered at different temperatures was investigated by immersion testing and electrochemical testing in a CO_2 aqueous environment. When the tempering temperature exceeded 500℃...The corrosion behavior of 5 wt%Cr steel tempered at different temperatures was investigated by immersion testing and electrochemical testing in a CO_2 aqueous environment. When the tempering temperature exceeded 500℃, the corrosion rate increased. The corrosion layers consisted of Cr-rich compounds, which affected the corrosion behaviors of the steels immersed in the corrosive solution. The results of electrochemical experiments demonstrated that 5 wt%Cr steels with different microstructures exhibited pre-passivation characteristics that decreased their corrosion rate. Analysis by electron back-scattered diffraction showed that the frequency of high-angle grain boundaries(HAGBs) and the corrosion rate were well-correlated in specimens tempered at different temperatures. The corrosion rate increased with increasing HAGB frequency.展开更多
Based on the mean yearly precipitation and the total yearly evaporation data of 295 meteorological stations in China in 1951-1999, the aridity index is calculated in this paper. According to the aridity index, the cli...Based on the mean yearly precipitation and the total yearly evaporation data of 295 meteorological stations in China in 1951-1999, the aridity index is calculated in this paper. According to the aridity index, the climatic regions in China are classified into three types, namely, arid region, semi-arid region and humid region. Dry and wet climate boundaries in China fluctuate markedly and differentiate greatly in each region in the past 50 years. The fluctuation amplitudes are 20-400 km in Northeast China, 40-400 km in North China, 30-350 km in the eastern part of Northwest China and 40-370 km in Southwest China. Before the 1980s (including 1980), the climate tended to be dry in Northeast China and North China, to be wet in the eastern part of Northwest China and very wet in Southwest China. Since the 1990s there have been dry signs in Southwest China, the eastern part of Northwest China and North China. The climate becomes wetter in Northeast China. Semi-arid region is the transitional zone between humid and arid regions, the monsoon edge belt in China, and the susceptible region of environmental evolution. At the end of the 1960s dry and wet climate in China witnessed abrupt changes, changing wetness into dryness. Dry and wet climate boundaries show the fluctuation characteristics of the whole shifts and the opposite fluctuations of eastward, westward, southward and northward directions. The fluctuations of climatic boundaries and the dry and wet variations of climate have distinctive interdecadal features.展开更多
We study the initial-boundary value problem of the Navier-Stokes equations for incompressible fluids in a general domain in R^n with compact and smooth boundary, subject to the kinematic and vorticity boundary conditi...We study the initial-boundary value problem of the Navier-Stokes equations for incompressible fluids in a general domain in R^n with compact and smooth boundary, subject to the kinematic and vorticity boundary conditions on the non-flat boundary. We observe that, under the nonhomogeneous boundary conditions, the pressure p can be still recovered by solving the Neumann problem for the Poisson equation. Then we establish the well-posedness of the unsteady Stokes equations and employ the solution to reduce our initial-boundary value problem into an initial-boundary value problem with absolute boundary conditions. Based on this, we first establish the well-posedness for an appropriate local linearized problem with the absolute boundary conditions and the initial condition (without the incompressibility condition), which establishes a velocity mapping. Then we develop apriori estimates for the velocity mapping, especially involving the Sobolev norm for the time-derivative of the mapping to deal with the complicated boundary conditions, which leads to the existence of the fixed point of the mapping and the existence of solutions to our initial-boundary value problem. Finally, we establish that, when the viscosity coefficient tends zero, the strong solutions of the initial-boundary value problem in R^n(n ≥ 3) with nonhomogeneous vorticity boundary condition converge in L^2 to the corresponding Euler equations satisfying the kinematic condition.展开更多
Based on the fuzzy local information c-means (FLICM) clustering algorithm, a new method is developed for extracting the equatorward and poleward boundaries of the auroral oval from images acquired by the Ultraviolet...Based on the fuzzy local information c-means (FLICM) clustering algorithm, a new method is developed for extracting the equatorward and poleward boundaries of the auroral oval from images acquired by the Ultraviolet Imager (UVI) aboard the POLAR satellite. First, the method iteratively segments the UVI image with the FLICM clustering algorithm, according to an integrity criterion for the segmented auroral oval. Then, possible gaps in the extracted auroral oval are filled, based on prior knowledge of its shape. To evaluate the method objectively, the extracted boundaries are compared with the precipitating electron boundaries determined from DMSP satellite precipitation particle data. The evaluation results demonstrate that the proposed method generates more accurate auroral boundaries than traditional methods.展开更多
A numerical method is presented that simulates 3D explosive field problems. A code MMIC3D using this method can be used to simulate the propagation and reflected effects of all kinds of rigid boundaries to shock waves...A numerical method is presented that simulates 3D explosive field problems. A code MMIC3D using this method can be used to simulate the propagation and reflected effects of all kinds of rigid boundaries to shock waves produced by an explosive source. These numerical results indicate that the code MMIC3D has the ability in computing cases such as 3D shock waves produced by air explosion, vortex region of the shock wave, the Mach wave, and reflected waves behind rigid boundaries.展开更多
基金supported by National Key Research and Development Program of China(No.2021YFB3400800)National Natural Science Foundation of China(Grant No.52271136,51901177)Natural Science Foundation of Shaanxi Province(No.2021JC-06,2019TD-020).
文摘Grain boundaries(GBs)play a crucial role on the structural stability and mechanical properties of Cu and its alloys.In this work,molecular dynamics(MD)simulations are employed to study the effects of Fe solutes on the formation energy,excess volume,dislocations and melting behaviors of GBs in CuFe alloys.It is illustrated that Fe solute affects the structural stability of Cu GBs substantially,the formation energy of GBs is reduced,but the thickness and melting point of GBs are increased,that is,the structural stability of Cu GBs is significantly improved owing to the Fe solutes.A strong scaling law exists between the formation energy,excess volume,thickness and melting point of GBs.Therefore,Fe solid solute plays an important role in the characteristics of GBs in bi-crystal Cu.
基金supported by the National Key Research and Development Program of China under Grant No.2023YFB3712401the National Natural Science Foundation of China under Grant Nos.12102254 and 12327802.
文摘The experimental results in previous studies have indicated that during the ductile fracture of pure metals,vacancies aggregate and form voids at grain boundaries.However,the physical mechanism underlying this phenomenon remains not fully understood.This study derives the equilibrium distribution of vacancies analytically by following thermodynamics and the micromechanics of crystal defects.This derivation suggests that vacancies cluster in regions under hydrostatic compression to minimize the elastic strain energy.Subsequently,a finite element model is developed for examining more general scenarios of interaction between vacancies and grain boundaries.This model is first verified and validated through comparison with some available analytical solutions,demonstrating consistency between finite element simulation results and analytical solutions within a specified numerical accuracy.A systematic numerical study is then conducted to investigate the mechanism that might govern the micromechanical interaction between grain boundaries and the profuse vacancies typically generated during plastic deformation.The simulation results indicate that the reduction in total elastic strain energy can indeed drive vacancies toward grain boundaries,potentially facilitating void nucleation in ductile fracture.
基金supported by the National Natural Science Foundation of China(Grant Nos.42090054,41931295)the Natural Science Foundation of Hubei Province of China(2022CFA002)。
文摘The frequent occurrence of extreme weather events has rendered numerous landslides to a global natural disaster issue.It is crucial to rapidly and accurately determine the boundaries of landslides for geohazards evaluation and emergency response.Therefore,the Skip Connection DeepLab neural network(SCDnn),a deep learning model based on 770 optical remote sensing images of landslide,is proposed to improve the accuracy of landslide boundary detection.The SCDnn model is optimized for the over-segmentation issue which occurs in conventional deep learning models when there is a significant degree of similarity between topographical geomorphic features.SCDnn exhibits notable improvements in landslide feature extraction and semantic segmentation by combining an enhanced Atrous Spatial Pyramid Convolutional Block(ASPC)with a coding structure that reduces model complexity.The experimental results demonstrate that SCDnn can identify landslide boundaries in 119 images with MIoU values between 0.8and 0.9;while 52 images with MIoU values exceeding 0.9,which exceeds the identification accuracy of existing techniques.This work can offer a novel technique for the automatic extensive identification of landslide boundaries in remote sensing images in addition to establishing the groundwork for future inve stigations and applications in related domains.
基金funded by the Saudi Aramco-KAIST CO_(2)Management Centersupported by a grant from the National Research Foundation of Korea+1 种基金funded by the Ministry of Science,ICT,and Future Planning(Grant no.2021K1A4A8A01079356)supported by the National Research Foundation of Korea(NRF)fund(NRF-2020M3H4A3081874).
文摘Spatial control of lithium deposition is the most important issue in lithium-metal batteries because of the considerable control of lithium dendrite suppression via the uniform distribution of Li^(+)flux.Although seed materials are crucial for the behavior of lithium deposition,in-depth studies on their physical and chemical control have not been conducted.Here,we describe a new design of seed structure comprising a wrinkled Cu/graphene substrate surrounded by copper(Ⅰ)oxide(Cu_(2)O)on a graphene grain boundary over a large area,which is fabricated by the oxidation of the Cu surface via graphene boundary defects by using chemical vapor deposition(CVD).Scanning and transmission electron microscopy results reveal that Cu_(2)O on the graphene boundary can render a preferential reaction with lithium during the first deposition and assist in the uniform deposition of lithium by preventing the agglomeration of lithium clusters during the second deposition.This two-step process is attributed to the degree of selectivity due to the difference in lithium affinity,which allows long-term electrochemical stability and a high rate capability via boundary effects.This study highlights the significance of the boundary effect,which can open new avenues for the formation of a large family of seed structures in lithium-metal batteries.
基金supported by the National Key R&D Program of China[grant number 2021YFA1200203]the Key Program of National Natural Science Foundation of China[grant number 51931003]+3 种基金the National Natural Science Foundation of China[grant numbers 52171118,52071178,51901103]the Projects in Science and Technique Plans of Ningbo City[grant number 2019B10083]the China Postdoctoral Science Foundation[grant number 2021M701715]the Opening Project of the Key Laboratory of Advanced Manufacturing and Intelligent Technology(Ministry of Education)of Harbin University of Science and Technology[grant number KFKT202103]
文摘Due to the insufficient slip systems in hexagonal close-packed structure,twinning is frequently activated to support stable plastic deformation of Mg alloy.In this work,we found four typical twin-like interfaces with misorientations of 102°,109°,142°and 149°,respectively,which had not only a shared[1120]zone axis of neighboring grains,but also overlapped diffraction spots similar to twins.However,highresolution transmission electron microscope(HRTEM)analysis revealed that the interfaces in real space deviated from the supposed twinning planes in reciprocal space,i.e.their overlapped diffraction spots.We clarified that the incoherent interfaces were co-axial grain boundaries(CGBs).Additionally,a special angle ofθ,close to 90°,between the interface and one side of basal plane,was frequently formed in CGBs.We proposed that interaction of multiple twinning contributes to the formation of CGBs,and theθis formed due to alternative tensile and compression twinning under a uniaxial loading.
基金financially supported by the National Ten Thousand Talent Program for Young Top-notch Talentthe National Natural Science Fund for Excellent Young Scholars (52022030)+8 种基金the National Natural Science Foundation of China (51972111,52203330)the Shanghai Pilot Program for Basic Research(22TQ1400100-5)the “Dawn” Program of Shanghai Education Commission (22SG28)the Shanghai Municipal Natural Science Foundation (22ZR1418000)the Science and Technology Innovation Plan of Shanghai Science and Technology Commission(22YF1410000)the Postdoctoral Research Foundation of China(2021M701190)the Fundamental Research Funds for the Central Universities (JKM01221621, JKM01221678)the Major Science and Technology Projects of Inner Mongolia Autonomous Region(2021ZD0042)Shanghai Engineering Research Center of Hierarchical Nanomaterials (18DZ2252400)。
文摘In recent years, perovskite solar cells(PSCs) have propelled into the limelight owing to rapid development of efficiency;however, the abundant defects at the perovskite grain boundaries result in unwanted energy loss and structural degradation. Here, the grain boundaries of perovskite polycrystalline films have been found to act as nanocapillaries for capturing perovskite quantum dots(PQDs), which enable the conformal assemble of PQDs at the top interspace between perovskite grains. The existence of PQDs passivated the surface defects, optimized the interfacial band alignments, and ultimately improved the power conversion efficiency from 19.27% to 22.47% in inverted PSCs. Our findings open up the possibility of selective assembly and structural modulation of the perovskite nanostructures towards efficient and stable PSCs.
文摘LetΓbe a Jordan curve in the complex plane and let Γ_(λ) be the constant distance boundary ofΓ.Vellis and Wu[10]introduced the notion of a(ζ,r_(0))-chordal property which guarantees that,whenλis not too large, Γ_(λ) is a Jordan curve whenζ=1/2 and Γ_(λ) is a quasicircle when 0<ζ<1/2.We introduce the(ζ,r_(0),t)-chordal property,which generalizes the(ζ,r_(0))-chordal property,and we show that under the condition thatΓis(ζ,r_(0),√t)-chordal with 0<ζ<r_(0)^(1−√t)/2,there existsε>0 such that Γ_(λ) is a t-quasicircle once Γ_(λ) is a Jordan curve when 0<λ<ε.In the last part of this paper,we provide an example:Γis a kind of Koch snowflake curve which does not have the(ζ,r_(0))-chordal property for any 0<ζ<1/2,however Γ_(λ) is a Jordan curve whenλis small enough.Meanwhile,Γhas the(ζ,r_(0),√t)-chordal property with 0<ζ<r_(0)^(1−√t)/2 for any t∈(0,1/4).As a corollary of our main theorem, Γ_(λ) is a t-quasicircle for all 0<t<1/4 whenλis small enough.This means that our(ζ,r_(0),t)-chordal property is more general and applicable to more complicated curves.
文摘植物顶端分生组织可分为中央区,周缘区和肋区。在植物胚后发育中,侧生器官产生于顶端分生组织的周缘区。顶端分生组织和侧生器官之间的边界的建立和维持是一个非常重要的发育过程,许多调节子参与控制这个过程。拟南芥的 LATERALORGANBOUNDARIES(LOB)基因具有独特的表达模式,其表达的范围与上述的边界区域重合。LOB基因隶属于一个大的基因家族——L O B 结构域基因家族。该家族编码的蛋白在 N 端具有一个保守的LOB结构域,该家族 LOB 基因以外的成员也参与拟南芥不同的发育过程。为了探讨在与拟南芥亲缘关系较远的豆科中 LOB 同源基因的功能,我们在豆科模式植物百脉根中分离了3 个 LOB 同源基因,命名为 LjLOB 基因,并用 RNA 原位杂交方法研究了这3个基因的表达模式。研究结果显示,L j L O B 1 和LjLOB3都强烈地在小叶原基的基部表达,这种表达模式可能与小叶原基和复叶原基之间的边界相关。而LjLOB4则在发育中的花芽不同轮之间的边界上表达。百脉根中这3 个基因具有不同的表达模式,强烈地提示它们的功能发生了分歧:L j L O B 1 和L j L O B 3 可能在复叶发育中具有重要功能;而LjLOB4 则可能参与了花的发育。
文摘By means of surface mechanical attrition treatment ( SMAT), the groin size with a diameter of aboat 60hm formed at about 20μm depth and numerous mechanical twins at about 50μm depth from the treated surface were synthesized in 316L stainless steel because of the different distributions of strain and strain rate along depth orientation. For instance the maximum strain rate reached 10^3-10^4s^-1 on the top surface. The relationship between the microsturcture and the corrosion property was studied in 0.05M H2SO4+ 0.25M Na2SO4 aqueous solution, and the results show an extreme improvement of corrosion resistance owing to the appearance of twin boundaries and the obvious reduction in corrosion resistance attributed to the presence of nanocrystaline boundaries.
基金supported by the National Natural Science Foundation of China(41002038)the National Major Fundamental Research and Development Projects(2012CB822002 and 2009CB219304)
文摘Just like in sedimentary stratigraphy, the factor for constructing volcanostratigraphic volcanostratigraphic boundary is an important framework. The fundamental factor of volcanostratigraphic boundaries is to classify the types and define their characteristics. Based on field investigation and cross-wells section analysis of Mesozoic volcanostratigraphy in NE China, 5 types of volcanostratigraphic boundaries have been recognized, namely eruptive conformity boundary (ECB), eruptive unconformity boundary (EUB), eruptive interval unconformity boundary (EIUB), tectonic unconformity boundary (TUB) and intrusive contacts boundary (ICB). Except ICB, the unconformity boundaries can be divided into angular unconformity and paraconformity. The time spans and signs of these boundaries are analyzed by using age data of some volcanic fields that have been published. The time spans of ECB and EUB are from several minutes to years. In lava flows, cooling crust is distributed above and below ECB and EUB; in pyroclastic flows, airfalls and lahars, a fine layer below these boundaries has no discernable erosion at every part of the boundary. EUB may be curved or cross curved and jagged. The scale of ECB/EUB is dependent on the scale of lava flow or pyroclastic flows. The time span of EIUB is from decades to thousands of years. There is also weathered crust under EIUB and sedimentary rock beds overlie EIUB. In most instances, weathered crust and thin sedimentary beds are associated with each other laterally. The boundary is a smooth curved plane. The scale of EIUB is dependent on the scale of the volcano or volcano groups. The characteristics of TUB are similar to EIUB's. The time interval of TUB is from tens of thousands to millions of years. The scale of TUB depends on the scale of the basin or volcanic field. Both the lab data and logging data of wells in the Songliao Basin reveal that the porosity is greatly related to the boundaries in the lava flows. There is a high-porosity belt below ECB, EUB or EIUB, and the porosity decreases when it is apart from the boundary. The high-porosity belt below ECB and EUB is mainly contributed by primary porosity, such as vesicles. The high-porosity belt below EIUB is mainly contributed by primary and secondary porosity, such as association of vesicles and spongy pores, so the area near the boundary in lava flows is a very important target for reservoirs.
基金Project supported by the Ministry of Science and Technology of China (2002BA315A-5)
文摘The behaviors of La and Ce on gram boundaries in carbon manganese clean steel were investigated by high-reso- lution transmission elecetron microscope (HRTEM), scanning elecetron microscopy(SEM ), energy dispersive spectrometer (EDS) and X-ray diffraction(XRD) analysis. The existing forms of rare earths (RE) in clean steel were as follows: dissolved in sohd solution, forming inclusion or second phase containing RE (RE-Fe-P, La-P, Fe-La eutectic and Fe-Ce phase). The dissolved La or Ce segregated at grain boundaries. The segregation of both S and P at gram boundaries was reduced with suitable RE content. The impact toughness of the steel was improved obviously. La and Ce had effecets on purifying molten steel and modifying inclusions in clean steel, whereas with excessive La or Ce, La-Fe-P, La-P and Fe-La eutecetic phase or Ce-Fe-P and Fe-Ce intermetallic compound would form along grain boundaries, causing the impact energy to decrease significantly.
文摘Almost all intraplate caprocks experienced strong deformation during the convergence of microplates, and then disintegrated into many secondary geologic units with the special characters, such as irregular boundaries and particular structural assemblages. In order to understand the formation mechanism of these special phenomena, a rheological experiment on the structural scenery of the Tongling area is carried out. The result shows that the primary regular and uniform boundaries of the Tongling area becomes irregular because of the enclosing and confinement of surrounding geological units in the process of 'compression-shearing-rotation-drag'; simultaneously, two specific 'drag depressions' developed at two opposite corners of the block. The former and the later phenomena can be regarded as a typical regional-scale rheological effect and necessary outcome of intraplate deformation respectively.
基金National Natural Science Foundation of China under Grant No.51478247National Key Research and Development Program of China under Grant No.2016YFC1402800
文摘The method of inputting the seismic wave determines the accuracy of the simulation of soil-structure dynamic interaction. The wave method is a commonly used approach for seismic wave input, which converts the incident wave into equivalent loads on the cutoff boundaries. The wave method has high precision, but the implementation is complicated, especially for three-dimensional models. By deducing another form of equivalent input seismic loads in the fi nite element model, a new seismic wave input method is proposed. In the new method, by imposing the displacements of the free wave fi eld on the nodes of the substructure composed of elements that contain artifi cial boundaries, the equivalent input seismic loads are obtained through dynamic analysis of the substructure. Subsequently, the equivalent input seismic loads are imposed on the artifi cial boundary nodes to complete the seismic wave input and perform seismic analysis of the soil-structure dynamic interaction model. Compared with the wave method, the new method is simplifi ed by avoiding the complex processes of calculating the equivalent input seismic loads. The validity of the new method is verifi ed by the dynamic analysis numerical examples of the homogeneous and layered half space under vertical and oblique incident seismic waves.
基金the Natural Science Foundation of China(No.5 99760 13 and1983 2 0 3 0 )
文摘This paper presents a method to generate unstructured adaptive meshes with moving boundaries and its application to CFD. Delaunay triangulation criterion in conjunction with the automatic point creation is used to generate 2 D and 3 D unstructured grids. A local grid regeneration method is proposed to cope with moving boundaries. Numerical examples include the interactions of shock waves with movable bodies and the movement of a projectile within a ram accelerator, illustrating an efficient and robust mesh generation method developed.
基金financially supported by the National Key R & D Program of China (No. 2017YFB0304900)the National Science and Technology Major Project of China (No. 2014E-3604)
文摘The corrosion behavior of 5 wt%Cr steel tempered at different temperatures was investigated by immersion testing and electrochemical testing in a CO_2 aqueous environment. When the tempering temperature exceeded 500℃, the corrosion rate increased. The corrosion layers consisted of Cr-rich compounds, which affected the corrosion behaviors of the steels immersed in the corrosive solution. The results of electrochemical experiments demonstrated that 5 wt%Cr steels with different microstructures exhibited pre-passivation characteristics that decreased their corrosion rate. Analysis by electron back-scattered diffraction showed that the frequency of high-angle grain boundaries(HAGBs) and the corrosion rate were well-correlated in specimens tempered at different temperatures. The corrosion rate increased with increasing HAGB frequency.
基金The Knowledge Innovation Project of CAS NO. KZCX1-10-06
文摘Based on the mean yearly precipitation and the total yearly evaporation data of 295 meteorological stations in China in 1951-1999, the aridity index is calculated in this paper. According to the aridity index, the climatic regions in China are classified into three types, namely, arid region, semi-arid region and humid region. Dry and wet climate boundaries in China fluctuate markedly and differentiate greatly in each region in the past 50 years. The fluctuation amplitudes are 20-400 km in Northeast China, 40-400 km in North China, 30-350 km in the eastern part of Northwest China and 40-370 km in Southwest China. Before the 1980s (including 1980), the climate tended to be dry in Northeast China and North China, to be wet in the eastern part of Northwest China and very wet in Southwest China. Since the 1990s there have been dry signs in Southwest China, the eastern part of Northwest China and North China. The climate becomes wetter in Northeast China. Semi-arid region is the transitional zone between humid and arid regions, the monsoon edge belt in China, and the susceptible region of environmental evolution. At the end of the 1960s dry and wet climate in China witnessed abrupt changes, changing wetness into dryness. Dry and wet climate boundaries show the fluctuation characteristics of the whole shifts and the opposite fluctuations of eastward, westward, southward and northward directions. The fluctuations of climatic boundaries and the dry and wet variations of climate have distinctive interdecadal features.
基金supported in part by the National Science Foundation under Grants DMS-0807551, DMS-0720925, and DMS-0505473the Natural Science Foundationof China (10728101)supported in part by EPSRC grant EP/F029578/1
文摘We study the initial-boundary value problem of the Navier-Stokes equations for incompressible fluids in a general domain in R^n with compact and smooth boundary, subject to the kinematic and vorticity boundary conditions on the non-flat boundary. We observe that, under the nonhomogeneous boundary conditions, the pressure p can be still recovered by solving the Neumann problem for the Poisson equation. Then we establish the well-posedness of the unsteady Stokes equations and employ the solution to reduce our initial-boundary value problem into an initial-boundary value problem with absolute boundary conditions. Based on this, we first establish the well-posedness for an appropriate local linearized problem with the absolute boundary conditions and the initial condition (without the incompressibility condition), which establishes a velocity mapping. Then we develop apriori estimates for the velocity mapping, especially involving the Sobolev norm for the time-derivative of the mapping to deal with the complicated boundary conditions, which leads to the existence of the fixed point of the mapping and the existence of solutions to our initial-boundary value problem. Finally, we establish that, when the viscosity coefficient tends zero, the strong solutions of the initial-boundary value problem in R^n(n ≥ 3) with nonhomogeneous vorticity boundary condition converge in L^2 to the corresponding Euler equations satisfying the kinematic condition.
基金supported by the National Natural Science Foundation of China (Grant nos.60872154,41031064,40904041,40974103)the National High Technology Research and Development Program of China (Grant no.2008AA121703)the Ocean Public Welfare Scientific Research Project, State Oceanic Administration of China (Grant no.201005017)
文摘Based on the fuzzy local information c-means (FLICM) clustering algorithm, a new method is developed for extracting the equatorward and poleward boundaries of the auroral oval from images acquired by the Ultraviolet Imager (UVI) aboard the POLAR satellite. First, the method iteratively segments the UVI image with the FLICM clustering algorithm, according to an integrity criterion for the segmented auroral oval. Then, possible gaps in the extracted auroral oval are filled, based on prior knowledge of its shape. To evaluate the method objectively, the extracted boundaries are compared with the precipitating electron boundaries determined from DMSP satellite precipitation particle data. The evaluation results demonstrate that the proposed method generates more accurate auroral boundaries than traditional methods.
文摘A numerical method is presented that simulates 3D explosive field problems. A code MMIC3D using this method can be used to simulate the propagation and reflected effects of all kinds of rigid boundaries to shock waves produced by an explosive source. These numerical results indicate that the code MMIC3D has the ability in computing cases such as 3D shock waves produced by air explosion, vortex region of the shock wave, the Mach wave, and reflected waves behind rigid boundaries.