Natural vibration and critical velocity of translating Timoshenko beam with non-homogeneous boundaries

In most practical engineering applications,the translating belt wraps around two fixed wheels.The boundary conditions of the dynamic model are typically specified as simply supported or fixed boundaries.In this paper,non-homogeneous boundaries are introduced by the support wheels.Utilizing the translating belt as the mechanical prototype,the vibration characteristics of translating Timoshenko beam models with nonhomogeneous boundaries are investigated for the first time.The governing equations of Timoshenko beam are deduced by employing the generalized Hamilton's principle.The effects of parameters such as the radius of wheel and the length of belt on vibration characteristics including the equilibrium deformations,critical velocities,natural frequencies,and modes,are numerically calculated and analyzed.The numerical results indicate that the beam experiences deformation characterized by varying curvatures near the wheels.The radii of the wheels play a pivotal role in determining the change in trend of the relative difference between two beam models.Comparing the results unearths that the relative difference in equilibrium deformations between the two beam models is more pronounced with smaller-sized wheels.When the two wheels are of equal size,the critical velocities of both beam models reach their respective minima.In addition,the relative difference in natural frequencies between the two beam models exhibits nonlinear variation and can easily exceed 50%.Furthermore,as the axial velocities increase,the impact of non-homogeneous boundaries on modal shape of translating beam becomes more significant.Although dealing with non-homogeneous boundaries is challenging,beam models with non-homogeneous boundaries are more sensitive to parameters,and the differences between the two types of beams undergo some interesting variations under the influence of non-homogeneous boundaries.

Modeling the Interaction between Vacancies and Grain Boundaries during Ductile Fracture

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.

Effects of Fe solid solute on grain boundaries of bi-crystal Cu: A molecular dynamics simulation

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.

INCOMPRESSIBLE LIMIT OF IDEAL MAGNETOHYDRODYNAMICS IN A DOMAIN WITH BOUNDARIES

We study the incompressible limit of classical solutions to compressible ideal magneto-hydrodynamics in a domain with a flat boundary.The boundary condition is characteristic and the initial data is general.We first establish the uniform existence of classical solutions with respect to the Mach number.Then,we prove that the solutions converge to the solution of the incompressible MHD system.In particular,we obtain a stronger convergence result by using the dispersion of acoustic waves in the half space.

Plasma induced grain boundaries to boost electrochemical reduction of CO_(2)to formate

Bismuth-based catalysts are highly promising for the electrochemical carbon dioxide reduction reaction(eCO_(2)RR)to formate product.However,achieving high activity and selectivity towards formate and ensuring long-term stability remains challenging.This work reports the oxygen plasma inducing strategy to construct the abundant grain boundaries of Bi/BiO_x on ultrathin two-dimensional Bi nanosheets.The oxygen plasma-treated Bi nanosheet(OP-Bi)exhibits over 90%Faradaic efficiency(FE)for formate at a wide potential range from-0.5 to-1.1 V,and maintains a great stability catalytic performance without significant decay over 30 h in flow cell.Moreover,membrane electrode assembly(MEA)device with OPBi as catalyst sustains the robust current density of 100 mA cm^(-2)over 50 h,maintaining a formate FE above 90%.In addition,rechargeable Zn-CO_(2)battery presents the peak power density of1.22 mW cm^(-2)with OP-Bi as bifunctional catalyst.The mechanism experiments demonstrate that the high-density grain boundaries of OP-Bi provide more exposed active sites,faster electron transfer capacity,and the stronger intrinsic activity of Bi atoms.In situ spectroscopy and theo retical calculations further elucidate that the unsaturated Bi coordination atoms between the grain boundaries can effectively activate CO_(2)molecules through elongating the C-O bond,and reducing the formation energy barrier of the key intermediate(^(*)OCOH),thereby enhancing the catalytic performance of eCO_(2)RR to formate product.

Extensive identification of landslide boundaries using remote sensing images and deep learning method

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.

Formation mechanism of co-axial grain boundaries in a Mg alloy

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.

Nano-capillary induced assemble of quantum dots on perovskite grain boundaries for efficient and stable perovskite solar cells

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.

Spatial Control of Lithium Deposition by Controlling the Lithiophilicity with Copper(Ⅰ)Oxide Boundaries

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.

CONSTANT DISTANCE BOUNDARIES OF THE t-QUASICIRCLE AND THE KOCH SNOWFLAKE CURVE

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.

Precipitation sequence of η phase along low-angle grain boundaries in Al-Zn-Mg-Cu alloy during artificial aging

The precipitation sequence of η（MgZn2） phase along low-angle grain boundaries in Al-Zn-Mg-Cu alloy was investigated by examining samples aged at 135 ℃ for various times from 5 min to 6 h. High resolution transmission electron microscopy （HRTEM） observations and energy dispersive X-ray spectroscopy （EDX） analysis indicate that the precipitation sequence of η phase along low-angle grain boundaries should be supersaturated solid solution （SSS）→vacancy-rich clusters （VRC）→GP Ⅱ zones→η＇→η. Based on the theory of non-equilibrium grain boundary segregation （NGS） and non-equilibrium grain boundary co-segregation （NGCS）, the excessive solute elements gradually segregate to the grain boundaries by the diffusion of the solute-vacancy complex during aging treatment. The grain boundary segregation plays an important role in the nucleation and growth of VRC, GP Ⅱ zones, η＇ phase as well as η phase.

百脉根类LATERAL ORGAN BOUNDARIES基因的分离及表达方式(英文)

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。

Seismic wave input method for three-dimensional soil-structure dynamic interaction analysis based on the substructure of artificial boundaries

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.

Behaviors of Lanthanum and Cerium on Grain Boundaries in Carbon Manganese Clean Steel

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.

Formation Mechanism of "Drag Depressions" and Irregular Boundaries in Intraplate Deformation

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.

Economic polarized trends,function and expanded boundaries of the Yangtze Delta Region

In the era of economic globalization,the concept of Economic Polarized Area comes into being as an effective vehicle to agglomerate the economic elements and sustain the economic lifeline of the region. Based on the region's specific development mode and construction form the concept is working in such a way that it will contribute to guide the economic development of the country and will play an important role in competing with other regions or countries in the world. Due to the high speed development of the last 30 years,the Yangtze Delta Region starts to show the features of Economic Polarized Area. But,compared with other world-class Economic Polarized Areas,the economic strength and the ability of the Yangtze Delta Region to drive the country's economic development is still very low and the competitive power is still very limited. Expanding the boundaries of the Economic Polarized Area of the Yangtze Delta may extend the economic hinterland of the core area of the Yangtze Delta Region,will lighten the pressures from the limited resource and promote the rationalization of the industrial structure in the Yangtze Delta Region's core area. With regard to the reasonable boundaries of the Yangtze Delta Region,there are different opinions and controversial arguments in political and academic circles. Starting from the idea of increasing the competitive power and improving the economic strength of the Yangtze Delta Region,the paper firstly is discussing the requirements to become a world-class Economic Polarized Area. In a second step an analysis of functional complementation and economic collaboration between the cities of an "extended" Yangtze Delta Region has been carried out by in particular considering the feasibility of integrating these "newly included" cities. The final result of the study is,that the Region should be expanded from the number of 16 cities to 37 cities,and the appended cities should be divided up into two categories:Wenzhou,Jinhua,Yancheng,Huaian,Maanshan,Wuhu,Tongling,Chaohu,Hefei,Chuzhou,Xuancheng should be taken as Preferred Extending Area,and Suqian,Xuzhou,Lianyungang,Lishui,Quzhou,Chizhou,Anqing,Bengbu,Huangshan,Suzhou (Anhui Province) should be taken as Retained Qualification Area.

Effect of the frequency of high-angle grain boundaries on the corrosion performance of 5wt%Cr steel in a CO2 aqueous environment

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.

Low-Angle Grain Boundaries in Sublimation Grown 6H-SiC Crystals

High-resolution X-ray diffractometry(HRXRD)was used to assess the quality of 6H-SiC crystals grown by sublimation method.The results show the occurrence of low-angle grain boundaries(LB)is close relative to the inclination of the crystal interface.At the central faceted region with 0°inclination the crystal is of high structural perfection.However,at the region close to the facet with less than 5°inclination LB occurs slightly and at the region close to the peripheral polytype ring with more than 5°inclination LB defect occurs heavily.The density of LB can be drastically reduced by decreasing radial temperature gradient that determines the shape of the crystal growth interface.

Numerical Simulation of the Protective Effect of Complex Boundaries Toward Shock Waves in a 3D Explosive Field

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.

Atomic scale structural characterization of {10 12} twin boundaries in zinc

The structure and the migration mechanisms of {10 12} twin boundaries（TBs） of pure zinc deformed by rolling were studied using high-resolution transmission electron microscopy（HRTEM） at atomic scale. We found the presence of basal/prismatic（BP/PB） planes serrations on {10 12} TBs and the coexistence of two kinds of TBs with different structures in the same {10 12} twin： TBs composed of {10 12} coherent twin boundaries（CTBs） plus short BP/PB serrations, and TBs composed of successive BP/PB segments without {10 12} CTBs. The formation of BP/PB serrations has no relation to the c/a ratio of hexagonal-closepacked（HCP） metals because the BP/PB serrations are energetically preferred and geometrically favored. Based on dislocation theory, we proposed the migration mechanisms of the TBs to be the glide of twinning dislocations（TDs） on the CTBs and the climb of interface dislocations（IDs） on the BP/PB segments.