Indentation behavior of a semi-infinite piezoelectric semiconductor under a rigid flat-ended cylindrical indenter

This paper theoretically studies the axisymmetric frictionless indentation of a transversely isotropic piezoelectric semiconductor(PSC)half-space subject to a rigid flatended cylindrical indenter.The contact area and other surface of the PSC half-space are assumed to be electrically insulating.By the Hankel integral transformation,the problem is reduced to the Fredholm integral equation of the second kind.This equation is solved numerically to obtain the indentation behaviors of the PSC half-space,mainly including the indentation force-depth relation and the electric potential-depth relation.The results show that the effect of the semiconductor property on the indentation responses is limited within a certain range of variation of the steady carrier concentration.The dependence of indentation behavior on material properties is also analyzed by two different kinds of PSCs.Finite element simulations are conducted to verify the results calculated by the integral equation technique,and good agreement is demonstrated.

A Footpad Structure with Reusable Energy Absorption Capability for Deep Space Exploration Lander:Design and Analysis

The footpad structure of a deep space exploration lander is a critical system that makes the initial contact with the ground,and thereby plays a crucial role in determining the stability and energy absorption characteristics during the impact process.The conventional footpad is typically designed with an aluminum honeycomb structure that dissipates energy through plastic deformation.Nevertheless,its effectiveness in providing cushioning and energy absorption becomes significantly compromised when the structure is crushed,rendering it unusable for reusable landers in the future.This study presents a methodology for designing and evaluating structural energy absorption systems incorporating recoverable strain constraints of shape memory alloys(SMA).The topological configuration of the energy absorbing structure is derived using an equivalent static load method(ESL),and three lightweight footpad designs featuring honeycomb-like Ni-Ti shape memory alloys structures and having variable stiffness skins are proposed.To verify the accuracy of the numerical modelling,a honeycomb-like structure subjected to compression load is modeled and then compared with experimental results.Moreover,the influence of the configurations and thickness distribution of the proposed structures on their energy absorption performance is comprehensively evaluated using finite element simulations.The results demonstrate that the proposed design approach effectively regulates the strain threshold to maintain the SMA within the constraint of maximum recoverable strain,resulting in a structural energy absorption capacity of 362 J/kg with a crushing force efficiency greater than 63%.

A Compensation Algorithm for Large Element Characterizing the Damage Evolution Process and Its Application to Structure Collisions

When simulating the process from elastic–plastic deformation,damage to failure in a metal structure collision,it is necessary to use the large shell element due to the calculation efficiency,but this would affect the accuracy of damage evolution simulation.The compensation algorithm adjusting failure strain according to element size is usually used in the damage model to deal with the problem.In this paper,a new nonlinear compensation algorithm between failure strain and element size was proposed,which was incorporated in the damage model GISSMO(Generalized incremental stress state dependent damage model)to characterize ductile fracture.And associated material parameters were calibrated based on tensile experiments of aluminum alloy specimens with notches.Simulation and experimental results show that the new compensation algorithm significantly reduces the dependence of element size compared with the constant failure strain model and the damage model with the linear compensation algorithm.During the axial splitting process of a circular tubular structure,the new compensation algorithm keeps the failure prediction errors low over the stress states ranging from shear to biaxial tension,and achieves the objective prediction of the damage evolution process.This study demonstrates how the compensation algorithm resolves the contradiction between large element size and fracture prediction accuracy,and this facilitates the use of the damage model in ductile fracture prediction for engineering structures.

Static strength and crashworthiness analysis of a train cowcatcher at a running speed of 160 km/h

The cowcatcher is one of the unique devices at the front end of the train, which can remove obstacles on the track by crashing before the vehicle body to ensure the safety of the train. When a collision accident happens, the cowcatcher serves as the first energy-absorbing structure to dissipate and guide the collision energy. The design of the existing cowcatcher of multiple units generally focuses on the good ability to remove obstacles, while the secondary function, the crashworthiness of orderly deformation under collision, still needs further research. In this study, a finite element model of structural static load and collision analysis was established under standard EN 15227, with the cowcatcher for 160 km/h train as the prototype. Then the solution and simulation process was accomplished under the environment of ANSYS and LS-DYNA. The analysis results showed that the structural static strength of the current cowcatcher met the requirements of the standard EN 15227, and the longitudinal stiffness was evenly distributed. When removing the obstacles with low mass, the impact force was small and the structure would not produce obvious deformation;when removing the obstacles with large mass, the impact force was large and the shear fracture might occur at the connection of the cowcatcher.

Study on Multi-Scale Tensile Strength and Tensile Strain of Calcium Silicate Hydrate Layered Nanocomposites Under External Physical Field

Calcium silicate hydrate(C-S-H)is the mainly strength source of cement-based materials,but there is little basic research.In this paper,molecular dynamics method is applied to analyze the multi-scale tensile strength and tensile strain of C-S-H layered materials under the condition of external physical fields(temperature and strain rate).The results show that the tensile strength and strain of C-S-H model decrease with temperature raises.The temperature(from 1 K to 600 K)has obvious influence on the tensile strain and strength of C-S-H layered materials.In addition,at(0.00025 ps^(-1)-0.001 ps^(-1)),the tensile strain and strength of C-S-H layered materials are less sensitive to strain rate.The whole model is closer to a 3-dimensional deformation.However,at(0.001 ps^(-1)-0.005 ps^(-1)),the dynamic load effect begins to increase,and the work done by the load per unit time increased.The tensile strain and strength of C-S-H layered materials indicates intensified by the change of strain rate.The energies are randomly distributed in the system,not concentrated in a certain area.

Genome-wide evolution of MAPKs family and their expression in response to bacterial infection in seahorse Hippocampus erectus

Seahorses have evolved many unique biological traits,including a male brood pouch,the absence of caudal and pelvic fins,and the lack of spleen and gut-associated lymphatic tissue.The mitogenactivated protein kinases(MAPKs)are known to be involved in various important biological processes including growth,differentiation,immunity,and stress responses.Therefore,we hypothesized that the adaptive evolution and expression of the MAPK gene family in seahorse may differ from those of other teleost species.We identified positive selection sites in the erk2,erk5,jnk1,and p38αMAPK genes of the lined seahorse Hippocampus erectus and tiger-tailed seahorse Hippocampus comes.A novel expression profile of MAPK cascade genes was found in seahorse larvae during the first day after birth based on the RNA-seq data of H.erectus,which refl ected vital signs of immune response to its parental immune system.The expression patterns of the four positively selected MAPK genes were analyzed following the bacterial challenge of Vibrio fortis,revealing their upregulation pattern in brood pouch and other immune tissues.This study enriched our knowledge of the evolution of the H.erectus MAPK subfamilies,and could help better understanding the functional role of MAPKs in teleosts.

A Shakedown Strength Based Parametric Optimization Technique and Its Application on an Airtight Module

In aerospace engineering,design and optimization of mechanical structures are usually performed with respect to elastic limit.Besides causing insufcient use of the material,such design concept fails to meet the ever growing needs of the light weight design.To remedy this problem,in the present study,a shakedown theory based numerical approach for performing parametric optimization is presented.Within this approach,strength of the structure is measured by its shakedown limit calculated from the direct method.The numerical method developed for the structural optimization consists of nested loops:the inner loop adopts the interior point method to solve shakedown problems pertained to fxed design parameters,while the outer loop employs the genetic algorithm to fnd optimal design parameters leading to the greatest shakedown limit.The method established is frst verifed by the classic plate-with-a-circular-hole example,and after that it is applied to an airtight module for determining few key design parameters.By carefully analyzing results generated during the optimization process,it is convinced that the approach can become a viable means for designing similar aerospace structures.

Fatigue Characterization on a Cast Aluminum Beam of a High-Speed Train Through Numerical Simulation and Experiments

The cast aluminum beam is a key structure for carrying the body-hung traction motor of a high-speed train;its fatigue property is fundamental for predicting the residual life and service mileage of the structure.To characterize the structural fatigue property,a finite element-based method is developed to compute the stress concentration factor,which is used to obtain the structural fatigue strength reduction factors.A full-scale fatigue test on the cast aluminum beam is designed and implemented for up to ten million cycles,and the corresponding finite element model of the beam is validated using the measured data of the gauges.The results show that the maximum stress concentration occurs at the fillet of the supporting seat,where the structural fatigue strength reduction factor is 2.45 and the calculated fatigue limit is 35.4 MPa.Moreover,no surface cracks are detected using the liquid penetrant test.Both the experimental and simulation results indicate that the cast aluminum beam can satisfy the service life requirements under the designed loading conditions.

Propagation of Rayleigh-type surface waves in a layered piezoelectric nanostructure with surface effects

This work investigates the dispersion properties of Rayleigh-type surface waves propagating in a layered piezoelectric nanostructure composed of a piezoelectric nanofilm over an elastic substrate.As one of the most important features of nanostructures,surface effects characterized by surface stresses and surface electric displacements are taken into account through the surface piezoelectricity theory and the nonclassical mechanical and electrical boundary conditions.Concrete expressions of the dispersion equation are derived,and numerical results are provided to examine the effects of several surface-related parameters,including the surface elasticity,surface piezoelectricity,surface dielectricity,surface density,as well as surface residual stress,on the dispersion modes and phase velocity.The size-dependent dispersion behaviors occurring with surface effects are also predicted,and they may vanish once the thickness of the piezoelectric nanofilm reaches a critical value.

Statistical Analyses of the Strengths of Particulate Reinforced Metal Matrix Composites(PRMMCs)Subjected to Multiple Tensile and Shear Stresses

For design and application of particulate reinforced metal matrix composites(PRMMCs),it is essential to predict the material strengths and understand how do they relate to constituents and microstructural features.To this end,a computational approach consists of the direct methods,homogenization,and statistical analyses is introduced in our previous studies.Since failure of PRMMC materials are often caused by time-varied combinations of tensile and shear stresses,the established approach is extended in the present work to take into account of these situations.In this paper,ultimate strengths and endurance limits of an exemplary PRMMC material,WC-Co,are predicted under three independently varied tensile and shear stresses.In order to cover the entire load space with least amount of weight factors,a new method for generating optimally distributed weight factors in an n dimensional space is formulated.Employing weight factors determined by this algorithm,direct method calculations were performed on many statistically equivalent representative volume elements(SERVE)samples.Through analyzing statistical characteristics associated with results the study suggests a simplified approach to estimate the material strength under superposed stresses without solving the difficult high dimensional shakedown problem.

智能时代中小学校长信息化领导力提升路径研究

中小学校长的信息化领导力是影响教育信息化发展的关键因素。在智能时代,人工智能、大数据等技术的发展对中小学校长的信息化领导力提出了更高的要求。为了解我国中小学校长信息化领导力的现状,并提供相应的提升路径,文章从信息化环境建设能力、信息化愿景规划能力、信息化管理能力和信息化教学应用能力四个方面,设计校长信息化领导力问卷量表,并开展大规模问卷调查。结果表明,我国中小学校长信息化领导力具有如下特征:在信息化环境建设方面,较为重视基础设施建设;在信息化愿景规划方面,期待人工智能在教学与管理中的应用,愿意积极推动教育服务供给社会化;在信息化管理方面,积极应用人工智能,探索完善教师绩效评估,赋能校园安全管理;在信息化教学应用方面,较为重视智能时代信息化教学与教研活动的开展,愿意邀请专家进行指导。基于此,文章对校长信息化领导力的发展提出建议:以国内教育改革需求为导向,真正提高校长的信息化管理能力与管理学校的效果;聚焦技术的发展,实现技术支持下的校长领导力变革;关注绩效评估,提升校长评估教育信息化建设效果与效益的能力。

Integrated Structures and Materials Design of Mechanical Components

In recent years,high fidelity numerical models simultaneously reflecting the behaviors of mechanical systems and their underlying materials have gradually become an indispensable part of modern mechanical and production engineering.In different contexts,the attempt to bridge me chanical engineering with materials science and to replace phenomenological models by the physical ones are named either as integrated computational materials engineering(ICME)or integrated structures and materi als design(ISMD).

Neoadjuvant camrelizumab(an anti-PD-1 antibody)plus chemotherapy or apatinib(a VEGFR-2 inhibitor)for initially unresectable stage II–III non-small-cell lung cancer:a multicentre,two-arm,phase 2 exploratory study

This multicentre,two-arm,phase 2 study aimed to explore the efficacy and safety of neoadjuvant camrelizumab plus chemotherapy or apatinib in patients with initially unresectable stage II–III non-small-cell lung cancer(NSCLC).Eligible patients regardless of PD-L1 expression received neoadjuvant camrelizumab 200 mg and platinum-doublet chemotherapy every 3 weeks(arm A)or those with PD-L1-positive tumors received neoadjuvant camrelizumab and apatinib 250 mg once daily(arm B),for 2–4 cycles,followed by surgery.The primary endpoint was major pathological response(MPR)rate.Thirty patients in arm A and 21 in arm B were enrolled.Surgery rates were 50.0%(15/30)in arm A and 42.9%(9/21)in arm B,with all patients achieving R0 resections.Of these patients,the MPR and pathological complete response rates were both 20.0%(95%CI 4.3–48.1)in arm A and were 55.6%(95%CI 21.2–86.3)and 11.1%(95%CI 0.3–48.2)in arm B,respectively.The corresponding objective response rates were 33.3%(95%CI 11.8–61.6)and 55.6%(95%CI 21.2–86.3).With a median follow-up of 22.4 months(95%CI 19.0–26.0),the median event-free survival was not reached(NR;95%CI 13.6-NR)in arm A and 16.8 months(95%CI 8.6-NR)in arm B.Grade 3 or above treatment-related adverse events occurred in eight(26.7%)patients in arm A and three(14.3%)in arm B.Biomarker analysis showed baseline TYROBP expression was predictive of treatment response in arm B.Neoadjuvant camrelizumab plus chemotherapy or apatinib exhibits preliminary efficacy and manageable toxicity in patients with initially unresectable stage II–III NSCLC.

珠海机场二号航站楼主楼屋盖钢结构施工模拟分析

网架结构是一种形式多变的空间网格结构,因其具有受力性能好、质量轻、刚度大、抗震性能好、造价低、成形容易等优点,广泛用于航站楼、飞机库、体育馆、影剧院、展览厅、车站等建筑屋盖。珠海机场二号航站楼主楼屋盖采用大跨度连续超长变曲率双曲面局部抽空钢网架结构体系。介绍了该屋盖的造型特征和结构体系组成,并针对其复杂性采用分区分块累计提升工艺进行施工,提出了施工顺序,给出了提升方案。阐述了主楼屋盖钢结构的施工步骤,对每一步的施工步骤进行了模拟分析,并对支撑胎架卸载后的网架结构施加了设计荷载,得到了主楼钢结构屋盖施工全过程的位移和应力指标,评价了设计荷载作用下主楼钢结构基于施工模拟的性能。将网架全过程监测与施工仿真模拟相结合,通过实际监测数据与仿真模拟中应力、应变值的对比分析,实时调整网架提升姿态及分块大小,实现了网架提升过程中受力状态的精准控制。结果表明:主楼钢结构屋盖的施工方案可行,提升过程中结构变形与内力满足要求;钢网架考虑施工过程的影响后,跨中竖向挠度增大,应采用可靠的措施减小挠度增大所带来的不利影响;钢网架从开始施工到最后成型的过程中,局部杆件受力模式由长细比控制变成受力控制,须加大截面;大跨度网架有必要在施工模拟卸载胎架后,按设计荷载输入施工模拟分析模型进行位移和应力比复核;网架实测的应力和位移与施工仿真模拟基本一致,表明了施工模拟分析的准确性。

人工智能在教育领域创新扩散的影响因素研究——基于TOE理论框架

人工智能技术的创新扩散研究是深入推进人工智能教育应用的关键。人工智能技术的快速发展推动了技术与教育的融合创新,促进了教育教学方式的变革。由于目前人工智能技术在教育领域的实践应用还处于初级阶段,教师对其在评价、管理等方面的独特优势仍在探索中。为推动人工智能在教育领域规模化、常态化应用,本研究以TOE理论为基础,从教师的视角出发,采用问卷调查方法,深入剖析技术、组织和环境三大维度的各因素对人工智能在教育领域中采纳扩散的影响。结果表明:潮流压力、政策法规、教育培训、安全性、相对技术优势、组织准备、管理者支持是影响人工智能在教育领域进一步创新扩散的重要因素,兼容性对人工智能技术的采纳扩散没有显著影响;从人口变量学的角度来看,教师的性别、教龄和所教学段对人工智能技术的采纳扩散均不存在显著性差异,仅学历对人工智能技术在教育中采纳扩散的态度存在显著性差异。在此基础上,结合人工智能的发展规律、创新扩散的机制以及发达国家在人工智能教育方面的政策要求,提出了促进我国人工智能技术在教育领域进一步采纳扩散的建议。

Novel perspective in transplantation therapy of mesenchymal stem cells:targeting the ferroptosis pathway

Ex vivo culture-amplified mesenchymal stem cells(MSCs)have been studied because of their capacity for healing tissue injury.MSC transplantation is a valid approach for promoting the repair of damaged tissues and replacement of lost cells or to safeguard surviving cells,but currently the efficiency of MSC transplantation is constrained by the extensive loss of MSCs during the short post-transplantation period.Hence,strategies to increase the efficacy of MSC treatment are urgently needed.Iron overload,reactive oxygen species deposition,and decreased antioxidant capacity suppress the proliferation and regeneration of MSCs,thereby hastening cell death.Notably,oxidative stress(OS)and deficient antioxidant defense induced by iron overload can result in ferroptosis.Ferroptosis may inhibit cell survival after MSC transplantation,thereby reducing clinical efficacy.In this review,we explore the role of ferroptosis in MSC performance.Given that little research has focused on ferroptosis in transplanted MSCs,further study is urgently needed to enhance the in vivo implantation,function,and duration of MSCs.

基于网络药理学和实验验证研究补血益母丸治疗产后腹痛的作用机制

本研究通过网络药理学和实验验证,探讨补血益母丸治疗产后腹痛的分子机制。通过TCMSP、SymMap、BATMAN-TCM和《中华人民共和国药典》筛选出补血益母丸的主要活性成分;采用GeneGards数据库获得产后腹痛相关疾病靶点;采用Cytoscape3.9.1软件和String数据库构建蛋白相互作用网络;通过DAVID6.8数据库对GO和KEGG信号通路进行分析;对分析结果构建“化合物-靶点”网络,采用动物实验验证网络核心靶点,采用免疫组化检测不完全流产模型大鼠相关蛋白的表达水平。网络学分析结果表明,补血益母丸中的40种潜在活性成分可能影响ESR1、PGR、MMP2等40个相关靶点,并调节HIF-1、TNF、雌激素等信号通路。免疫组化结果显示,模型大鼠ERα、PR、MMP2蛋白表达水平均显著升高(P<0.01)。给予补血益母丸后,PR表达水平升高(P<0.01),ERα和MMP2表达水平显著降低(P<0.05或P<0.01)。补血益母丸可通过多成分、多靶点、多途径治疗产后腹痛,可通过调节雌孕激素受体,改善胶原代谢,从而促进产后子宫恢复。

Vanadium-based cathodes for aqueous zinc ion batteries: Structure,mechanism and prospects

As an emerging energy storage device with high-safety aqueous electrolytes, low-cost, environmental benignity and large-reserves, the rechargeable aqueous zinc-ion batteries(AZIBs) have attracted more and more attention. Vanadium-based compounds are also supposed as the potential candidate cathode materials for AZIBs due to their wide variety of phases, variable crystal structures and high theoretical capacity. In this review, the recent progress in the development of vanadium-based materials was summarized,and the relationship between the crystal structure types of active materials and Zn-ion transport mechanism was highlighted. During the charge-discharge process, the different electrostatic repulsion between the cations of vanadium-based compounds with different crystal structures and Zn^(2+)results in a variety of the Zn-ion storage mechanisms, which can be significant guidance for designing the advanced batteryelectrode materials for AZIBs. Furthermore, other factors associated with the storage mechanisms, such as electrolyte components and electrode morphology, are discussed. Finally, the strategies to improve the electrical conductivity, inhibit the dissolution and stabilize the crystal structure of vanadium-based compounds are proposed and the future prospects for developing high-energy-density AZIBs are presented.

Superior corrosion resistance and corrosion mechanism of dual-main-phase (Ce_(15)Nd_(85))_(30)Fe_(bal)B_(1)M magnets in different solutions

The electrochemical corrosion behavior of both (Ce_(15)Nd_(85))_(30)Fe_(bal)B_(1)M sintered magnets prepared with dual-main-phase method and N45-type magnets was studied in 3.5 wt% NaCl,1.1 wt% NaH_(2)PO_(4),and 2.5 wt% NaOH solutions,respectively.The (Ce_(15)Nd_(85))_(30)Fe_(bal)B_(1)M sintered magnets perform superior corrosion resistance than N45-type magnets in the tested solutions.In general,two kinds of magnets exhibit the best corrosion resistance property in 2.5 wt% NaOH solution,while the worst in 3.5 wt% NaCl solution.Microstructures of samples before and after corrosion were investigated.With the addition of Ce by means of dual-main-phase method,which is conducive to facilitating low-temperature sintering and grain refinement,uniform grain size and(Nd,Ce)-rich phase distribution form,give rise to narrow and thin corrosion channels.Moreover,the corrosion rate of the(Nd,Ce)-rich phase is lower than that of Nd-rich one.Acco rdingly,corro sion re sistance of (Ce_(15)Nd_(85))_(30)Fe_(bal)B_(1)M sintered magnet is superior when compared with the commercial N45-type magnet which has comparable magnetic properties.

Magnetic properties,crystalline and magnetic microstructures of dual-main-phase(Nd,Ce)-Fe-B sintered magnets

The(Nd,Ce)-Fe-B sintered magnets were prepared by a dual-main-phase(DMP)process under the same conditions using different combinations of Nd-Fe-B with Ce-Fe-B and(Nd,Ce)-Fe-B strips.The crystalline and magnetic microstructures of DMP(Nd,Ce)-Fe-B magnets with the remanence of 11.92-12.68 kGs,the intrinsic coercivity of 3.97-5.31 kOe,and the maximum energy product of 23.08-32.99 MGOe have been investigated.Magnetic force microscope(MFM)investigations reveal that the DMP(Nd,Ce)-Fe-B magnets show maze-like patterns,which are like that of standard anisotropy Nd-Fe-B sintered magnets by and large.However,much finer domain structures mixing with coarse ones can be observed obviously in DMP(Nd,Ce)-Fe-B sintered magnets.The size distribution of the domain width of the DMP(Nd,Ce)-Fe-B magnet is not uniform obviously.The average domain width is W=0.912μm,and the fine domain width has only 0.216μm.The smaller domain width and more branch domain patterns exist in poorer coercivity DMP magnets.This is caused by the non-uniform Ce composition of poorer property DMP magnets and the grain boundary microstructure that is not conducive to improving the coercivity.Furthermore,it is found that some domains of rare-earth-rich grain boundary phases exhibit the characteristics of plate-like patterns rather than no-contrast by using MFM,indicating their ferromagnetism.Obvious correlations between the crystalline microstructure,chemical composition of phases,and magnetic structure were demonstrated for the DMP magnets.