原子级制造测量与表征研究现状综述

原子级制造是指将能量作用于原子,通过原子级材料的可控去除或者原子/分子级结构的大规模操控及组装,实现产品性能与功能跃迁的前沿制造技术,是一种可以大规模、批量化的先进制造技术。该过程需要在10-10m空间尺度下精确操控原子。同时,制造过程中原子的键合时间、电子动力学变化均发生在飞秒(10-15s)至阿秒(10-18s)量级。因此,只有具备超快时间和空间分辨在线检测与表征能力,才能够深入了解并利用原子级制造过程中原子尺度的新原理、新效应,保障原子级制造的可达性与可控性;只有实现原子级制造过程的高通量、大范围的在线监测,才能保障原子级制造的可靠性。基于此,原子级制造的测量与表征是指在原子级的时间、空间、能量尺度上对材料、结构或器件进行精确的测量和表征,以保障原子级制造的可达性、可控性与可靠性。本文介绍了原子级制造所需的测量表征手段的研究现状,从原子级超快动力学过程观测、原子结构演变原位表征、原子级制造过程在线质量监测三大方向进行系统梳理,总结了目前原子级制造测量与表征的挑战并针对未来发展给出建议。

Bionic lightweight design of limb leg units for hydraulic quadruped robots by additive manufacturing and topology optimization

Galloping cheetahs,climbing mountain goats,and load hauling horses all show desirable locomotion capability,which motivates the development of quadruped robots.Among various quadruped robots,hydraulically driven quadruped robots show great potential in unstructured environments due to their discrete landing positions and large payloads.As the most critical movement unit of a quadruped robot,the limb leg unit(LLU)directly affects movement speed and reliability,and requires a compact and lightweight design.Inspired by the dexterous skeleton–muscle systems of cheetahs and humans,this paper proposes a highly integrated bionic actuator system for a better dynamic performance of an LLU.We propose that a cylinder barrel with multiple element interfaces and internal smooth channels is realized using metal additive manufacturing,and hybrid lattice structures are introduced into the lightweight design of the piston rod.In addition,additive manufacturing and topology optimization are incorporated to reduce the redundant material of the structural parts of the LLU.The mechanical properties of the actuator system are verified by numerical simulation and experiments,and the power density of the actuators is far greater than that of cheetah muscle.The mass of the optimized LLU is reduced by 24.5%,and the optimized LLU shows better response time performance when given a step signal,and presents a good trajectory tracking ability with the increase in motion frequency.

Observer-Based Adaptive Robust Precision Motion Control of a Multi-Joint Hydraulic Manipulator

Hydraulic manipulators are usually applied in heavy-load and harsh operation tasks.However,when faced with a complex operation,the traditional proportional-integral-derivative(PID)control may not meet requirements for high control performance.Model-based full-state-feedback control is an effective alternative,but the states of a hydraulic manipulator are not always available and reliable in practical applications,particularly the joint angular velocity measurement.Considering that it is not suitable to obtain the velocity signal directly from differentiating of position measurement,the low-pass filtering is commonly used,but it will definitely restrict the closed-loop bandwidth of the whole system.To avoid this problem and realize better control performance,this paper proposes a novel observerbased adaptive robust controller(obARC)for a multi-joint hydraulic manipulator subjected to both parametric uncertainties and the lack of accurate velocity measurement.Specifically,a nonlinear adaptive observer is first designed to handle the lack of velocity measurement with the consideration of parametric uncertainties.Then,the adaptive robust control is developed to compensate for the dynamic uncertainties,and the close-loop system robust stability is theoretically proved under the observation and control errors.Finally,comparative experiments are carried out to show that the designed controller can achieve a performance improvement over the traditional methods,specifically yielding better control accuracy owing to the closed-loop bandwidth breakthrough,which is limited by low-pass filtering in fullstate-feedback control.

Rapid testing and prediction of soil–water characteristic curve of subgrade soils considering stress state and degree of compaction

The subgrade soil is generally in saturated or unsaturated condition. To analyze complex thermo-hydro-mechanical-chemical (THMC) behaviors of subgrade, it is essential to determine the soil–water characteristic curve (SWCC) that represents the relationship between matric suction and moisture content. In this study, a full-automatic rapid stress-dependent SWCC pressure-plate extractor was developed. Then, the influences of overburden stress and degree of compaction on the SWCC of subgrade soil such as high liquid limit silt (MH) and low liquid limit clay (CL) were analyzed. Accordingly, a new model taking into account the influences of overburden stress and degree of compaction based on the well-known Van Genuchten (VG) SWCC fitting model was presented and validated. The results show that with the increase of the degree of compaction and overburden stress, the saturated moisture content of subgrade soil decreases, while the air-entry value increases and the transition section curve becomes flat. The influences of the degree of compaction and overburden stress on the SWCC of MH is greater than that of CL. Meanwhile, there was a satisfactory agreement between the prediction and measurement, indicating a good performance of the new model for predicting the SWCC.

Effects of specific doses of E-beam irradiation which inactivated SARS-CoV-2 on the nutrition and quality of Atlantic salmon

The contamination of Atlantic salmon with severe acute respiratory syndrome coronavirus 2(SARS-CoV-2)has impeded the development of the cold-chain food industry and posed possible risks to the population.Electron beam(E-beam)irradiation under 2,4,7,and 10 kGy can effectively inactivate SARS-CoV-2 in cold-chain seafood.However,there are few statistics about the quality changes of salmon exposed to these irradiation dosages.This work demonstrated that E-beam irradiation at dosages capable of killing SARS-CoV-2 induced lipid oxidation,decreased vitamin A content,and increased some amino acids and ash content.In addition,irradiation altered the textural features of salmon,such as its hardness,resilience,cohesiveness,and chewiness.The irradiation considerably affected the L*,a*,and b*values of salmon,with the L*value increasing and a*,b*values decreasing.There was no significant difference in the sensory evaluation of control and irradiated salmon.It was shown that irradiation with 2−7 kGy E-beam did not significantly degrade quality.The inactivation of SARS-CoV-2 in salmon is advised at a dose of 2 kGy.

共享型领导如何影响团队绩效——基于MASEM的多重中介模型检验

共享型领导模式为团队提升绩效提供了新思路。为了探究共享型领导提升团队绩效的中介机制,本文从认知过程、情感过程和行为过程三个视角出发构建了一个多重中介模型,并运用元分析结构方程模型(MASEM),对来自398项实证研究的511个独立效应量(约29607个团队样本)进行了梳理和分析。研究结果表明:团队信心、团队信任和团队学习行为在共享型领导与团队绩效的正向关系中起积极的中介作用;相比于团队信心和团队信任,团队学习行为在中介共享型领导与团队绩效的正向关系中起主导作用。研究结果揭示了共享型领导对于团队绩效的影响机理,为实践管理者提升团队绩效贡献了新思路,并为未来研究指明了方向。

Research and Development of Electro‑hydraulic Control Valves Oriented to Industry 4.0:A Review

Electro-hydraulic control valves are key hydraulic components for industrial applications and aerospace,which controls electro-hydraulic motion.With the development of automation,digital technology,and communication technology,electro-hydraulic control valves are becoming more digital,integrated,and intelligent in order to meet the requirements of Industry 4.0.This paper reviews the state of the art development for electro-hydraulic control valves and their related technologies.This review paper considers three aspects of state acquisition through sensors or indirect acquisition technologies,control strategies along with digital controllers and novel valves,and online maintenance through data interaction and fault diagnosis.The main features and development trends of electro-hydraulic control valves oriented to Industry 4.0 are discussed.

Influence of Piston Number on Churning Losses in Axial Piston Pumps

Raising the rotational speed of an axial piston pump is useful for improving its power density;however,the churning losses of the piston increase significantly with increasing speed,and this reduces the performance and efficiency of the axial piston pump.Currently,there has been some research on the churning losses of pistons;however,it has rarely been analyzed from the perspective of the piston number.To improve the performance and efficiency of the axial piston pump,a computational fluid dynamics(CFD)simulation model of the churning loss was established,and the effect of piston number on the churning loss was studied in detail.The simulation analysis results revealed that the churning losses initially increased as the number of pistons increased;however,when the number of pistons increased from six to nine,the torque of the churning losses decreased because of the hydrodynamic shadowing effect.In addition,in the analysis of cavitation results,it was determined that the cavitation area of the axial piston pump was mainly concentrated around the piston,and the cavitation became increasingly severe as the speed increased.By comparing the simulation results with and without the cavitation model,it was observed that the cavitation phenomenon is beneficial for the reduction of churning losses.In this study,a piston churning loss test rig that can eliminate other friction losses was established to verify the accuracy of the simulation results.A comparative analysis indicated that the simulation results were consistent with the actual situation.In addition,this study also conducted a simulation study on seven and nine piston pumps with the same displacement.The simulation results revealed that churning losses of the seven pistons were generally greater than those of the nine pistons under the same displacement.In addition,regarding the same piston number and displacement,reducing the pitch circle radius of piston bores is effective in reducing the churning loss.This research analyzes the effect of piston number on the churning loss,which has certain guiding significance for the structural design and model selection of axial piston pumps.

Modeling and Parameter Sensitivity Analysis of Valve‑Controlled Helical Hydraulic Rotary Actuator System

As a type of hydraulic rotary actuator,a helical hydraulic rotary actuator exhibits a large angle,high torque,and compact structure;hence,it has been widely used in various fields.However,its core technology is proprietary to several companies and thus has not been disclosed.Furthermore,the relevant reports are primarily limited to the component level.The dynamic characteristics of the output when a helical rotary actuator is applied to a closed-loop system are investigated from the perspective of driving system design.Two main aspects are considered:one is to establish a reliable mathematical model and the other is to consider the effect of system parameter perturbation on the output.In this study,a detailed mechanical analysis of a helical rotary hydraulic cylinder is first performed,factors such as friction and load are considered,and an accurate dynamic model of the actuator is established.Subsequently,considering the nonlinear characteristics of pressure flow and the dynamic characteristics of the valve,a dynamic model of a valve-controlled helical rotary actuator angle closed-loop system is described based on sixth-order nonlinear state equations,which has never been reported previously.After deriving the system model,a sensitivity analysis of 23 main parameters in the model with a perturbation of 10%is performed under nine operating conditions.Finally,the system dynamics model and sensitivity analysis results are verified via a prototype experiment and co-simulation,which demonstrate the reliability of the theoretical results obtained in this study.The results provide an accurate mathematical model and analysis basis for the structural optimization or control compensation of similar systems.

Raising the Speed Limit of Axial Piston Pumps by Optimizing the Suction Duct

The maximum delivery pressure and the maximum rotational speed determine the power density of axial piston pumps.However,increasing the speed beyond the limit always accompanies cavitation,leading to the decrease of the volumetric efficiency.The pressure loss in the suction duct is considered a significant reason for the cavitation.Therefore,this paper proposes a methodology to optimize the shape of the suction duct aiming at reducing the intensity of cavitation and increasing the speed limit.At first,a computational fluid dynamics(CFD)model based on the full cavitation model(FCM)is developed to simulate the fluid field of the axial piston pump and a test rig is set to validate the model.Then the topology optimization is conducted for obtaining the minimum pressure loss in the suc-tion duct.Comparing the original suction duct with the optimized one in the simulation model,the pressure loss in the suction duct gets considerable reduction,which eases the cavitation intensity a lot.The simulation results prove that the speed limit can increase under several different inlet pressures.

The effect of soil moisture on the response by fungi and bacteria to nitrogen additions for N_(2)O production

In addition to bacteria,the contribution of fungi to nitrous oxide(N_(2)O)production has been recognized but the responses of these two broad and unrelated groups of microorganisms to global environmental changes,atmospheric nitrogen(N)deposition,and precipitation in terms of N_(2)O production are unclear.We studied how these two microbial-mediated N_(2)O production pathways responded to soil moisture conditions and to N addition in an N-limited temperate forest.Soils from a long-term N addition experiment in Changbai Mountain,northeastern China were incubated.Varied concentrations of cycloheximide and streptomycin,both inhibitors of fungal and bacterial activity,were used to determine the contributions of both to N_(2)O production in 66%,98%and 130%water-filled pore spaces(WFPS).The results showed that N_(2)O production decreased significantly with increasing cycloheximide concentration whereas streptomycin was only inhibiting N_(2)O emissions at 98%and 130%WFPS.The bacterial pathway of N_(2)O production in N-addition(Nadd)soil was significantly more dominant than that in untreated(Namb)soil.The difference in the fungal pathway of N_(2)O production between the soil with nitrogen addition and the untreated soil was not significant.Net N_(2)O emissions increased with increasing soil moisture,especially at 130%WFPS,a completely flooded condition.Bacteria dominated carbon dioxide(CO_(2))and N_(2)O emissions in Nadd soil and at 130%WFPS regardless of N status,while fungi dominated CO_(2)and N_(2)O emissions in soil without N addition at 66%and 98%WFPS.The results suggest that flooded soil is an important source of N_(2)O emissions and that bacteria might be better adapted to compete in fertile soils under anoxic conditions.

Low-Temperature Baking Effect of the Radio-Frequency Nb_(3)Sn Thin Film Superconducting Cavity

The Nb_(3)Sn thin film cavity,having the potential to be operated at a higher temperature and higher gradient compared to the cavity made from bulk niobium,is one of the most promising key technologies for the nextgeneration radio-frequency superconducting accelerators.In our work,several 1.3 GHz single-cell TESLA-shaped Nb_(3)Sn thin film cavities,coated by the vapor diffusion method,were tested at Peking University and Institute of Modern Physics,Chinese Academy of Sciences.It was observed that the performance of the Nb_(3)Sn thin film cavities in the tests without the slow cooling down procedure and the effective magnetic field shielding was significantly improved by using a low temperature baking at 100℃for 48 hours.Although the peak electric field of the cavity remained unchanged,the rapid drop of the unloaded Q value(Q0)with the increasing accelerating field(Q-slope)was effectively eliminated,resulting in an improvement of the Q0 in the intermediate field region by~8 times.Furthermore,under better test conditions with the shielded magnetic field less than 5 mG and the slow cooling down procedure in the temperature range of 25-15 K,the Q0 was still improved by about 20%.Our study shows that the low temperature baking can be an effective supplement to the effective post-treatment for the Nb_(3)Sn thin film cavity.

Assessment of Environmental Carrying Capacity Using Principal Component Analysis

Regional environmental carrying capacity (ECC) is nonlinear and spatially specific. A hierarchy index system including resources, environmental and socio-economic elements was established using an analytic hierarchy process. Principal component analysis (PCA) was used to estimate the regional size and differences of environmental carrying capacities. Main information of four principal components, i.e., carrying capacity of resources supply, carrying capacity of environmental quality, carrying capacity of social economy and carrying capacity of infrastructure construction, was extracted. The ECC evaluation value was divided into five levels of lowest carrying capacity, low carrying capacity, medium carrying capacity, high carrying capacity and highest carrying capacity, respectively. The results showed that on the whole ECC was at the medium carrying capacity level. ECC was generally highest in Guanzhong plain, followed by Loess Plateau, and was lowest in Qiba mountain. The carrying capacity of water resources and environmental quality was relatively low, and the infrastructure carrying capacity was highest among the four components. The temporal spatial variation of ECC was closely related to vulnerability of the natural resources and environment in the regions. Verification was proven that PCA was a useful tool when applied to evaluate ECC and reflect the spatial distribution of large-quantity ECC indices on a large regional scale. This study provides a basis for comprehensive understanding of resources, environment and management for regional balanced development.

基于微型钢管桩在地基处理施工工艺的研究

本文结合贵州铜仁G354石千香树园至河坝公路改扩建工程,桥梁、路基边坡建设当中工程地质条件变化多样,大多情况下难以满足工程地基承载力和变形要求,而又难以进行地基处理,需考虑桩基础方案。从现场踏勘并确定对原设计方案进行变更,对水泥搅拌桩、高压旋喷桩、微型钢管桩三种方案进行比选,择优选取微型钢管桩方案。通过采用泡沫混凝土作为路基填料以减少路基荷载;利用微型桩地基处理,将部分泡沫混凝土的荷载传递至基岩,并改善微型桩位置处的土体参数。其中直径小而高强的微型钢管桩适用性强,施工便捷高效,成为许多需桩基础处理地基的首选。因此,对微型钢管桩施工工艺的研究是至关重要的。

Mesenchymal stem cell-derived exosomes: Versatile nanomaterials for skin wound treatment

Accumulating studies reveal that mesenchymal stem cells(MSCs)promote skin wound healing mainly through the paracrine effects.Exosomes,one of the crucial paracrine mediators in wound healing,are cell-derived nanosized membranous vesicles containing diverse bioactive cargoes.With the potent ability of modulating skin cell behaviors,MSC-derived exosomes(MSC-Exos)are regarded as a promising nanomaterial for regenerative wound therapy.Under hostile conditions,MSC-Exos are efficient in protecting skin cells from severe damage and restoring their function.According to recent studies,MSC-Exos possess remarkable pro-healing effects in a variety of skin wounds,typically resulting in increased wound closure,inhibited scar tissue formation,and better restoration of skin function.To further enhance the therapeutic potential of MSC-Exos,the development of applicable pretreatment strategies and the optimization of exosome delivery are under intensive investigation.Herein,we summarize current research progress of MSC-Exos for skin wound treatment,with an emphasis on the biological effects of these nanovesicles,the repair mechanisms,and future challenges in clinical translation.

Coupled evolution of piston asperity and cylinder bore contour of piston/cylinder pair in axial piston pump

The wear condition of the piston/cylinder pair is crucial to the performance and reliability of the axial piston pump.The hard piston surface,the soft cylinder bore surface,and the interface oil film affects each other during the wear process.Specifically,in the mixed lubrication region,the geometry of the hard piston surface asperity directly affects the wear of soft cylinder bore surface,while the asperities may deform or even degrade when penetrating and sliding against the cylinder bore.So far,there is no suitable method to simulate their coupled evolution.This paper proposed a wear process simulation model considering the real-time interaction between the elasto-plastic deformation of the piston surface asperity,the wear contour of the cylinder bore,and the lubrication condition of the interface.An offline library of the elasto-plastic constitutive behavior of the asperity based on the finite element method(FEM)is established as a part of the simulation model to precisely analyze the deformation and degradation of the asperity and quickly invoke them in the numerical wear process simulation.The simulation and experimental results show that the piston asperity and the cylinder bore contour converge to a steady state after running-in for about 0.5 h.The distribution of the simulated asperity degradation and wear depth is also verified by the experiment.

Performance optimization for high speed axial piston pump considering cylinder block tilt

Increasing the rotating speed is considered as an efficient approach to upgrade the power-to-weight ratio in an axial piston pump,but penalized by more leakage and more severe wear resulting from the adverse cylinder block tilt.Previous studies mainly focused on the bearing characteristic of the valve plate/cylinder block pair,but the spline coupling also plays a key role in the undesired cylinder block tilt,which has been little studied.A theoretical model for the rotating assembly is presented to investigate the effect of the spline coupling length on the cylinder block tilt and the performance of the valve plate/cylinder block pair.A typical high-speed axial piston pump with the displacement of 5.2 mL/r at 10000 r/min was studied by simulation and experiment.It shows that the optimal spline coupling length is one value increased by 2 mm from the original,bringing a remarkable leakage reduction under the high-speed condition by decreasing the cylinder block tilting angle.The experiment result matches well with the simulation.The influences of the spline coupling on the cylinder block tilt and the leakage were demonstrated.

Synoptic-Scale Analysis on Development and Maintenance of the 19–21 July 2021 Extreme Heavy Rainfall in Henan,Central China

In this paper,synoptic-scale analyses of frontogenesis,moisture budget,and tropospheric diabatic heating are performed to reveal the development and maintenance mechanisms for the extreme heavy rainfall in Henan Province of central China from 19 to 21 July 2021,based on station observations and the ECMWF Reanalysis version 5(ERA5)data.The results demonstrate that owing to the blocking effect of local topography,low-level wind convergence in Henan appeared underneath high-level divergence,conducive to development and maintenance of a midtropospheric low-pressure system saddled by the Asian continental high and the western Pacific subtropical high(WPSH),during the extreme heavy rainfall.In the lower troposphere,frontogenesis occurred in the θ_(se) intensive region,as a result of the divergence and horizontal deformation(which play equally important roles),generating frontal secondary circulation with strong vertical motion favorable to heavy rainfall.Moisture budget analysis reveals that 1)with the continuous strengthening of the easterly wind from the north side of Typhoon In-Fa(2106),strong wind shear and orographic uplift led to abnormally strong convergence of water vapor flux in the boundary layer in Henan;2)there occurred extremely strong net inflow of moisture in the boundary layer from the east.Horizontally,both the apparent heat source and the moisture sink coincided with the area of heavy rainfall;vertically,however,Q_(1)exhibited a single peak with the heating center in the middle and upper troposphere,while large Q_(2)values evenly resided over 850–400 hPa;and Q_(1)(Q_(2))was dominated by vertical(horizontal)transport of potential temperature(moisture).These indicate that the latent heat release from condensation of initial heavy rainfall provided a positive feedback,leading to increasingly heavy precipitation.All these synoptic settings sustained the extreme rainfall process.

A stability locomotion-control strategy for quadruped robots with center-of-mass dynamic planning

Locomotion stability is essential for controlling quadruped robots and adapting them to unstructured terrain.We propose a control strategy with center-of-mass(CoM)dynamic planning for the stable locomotion of these robots.The motion trajectories of the swing legs are synchronized with the CoM of the robot.To implement the synchronous control scheme,we adjusted the swing legs to form a support triangle.The strategy is applicable to both static walk gait and dynamic trot gait.In the motion control processes of the robot legs,the distribution of the ground reaction forces is optimized to minimize joint torque and locomotion energy consumption.We also used an improved joint-torque controller with varied controller coefficients in the stance and swing phases.The simulation and experimental results demonstrate that the robot can complete omnidirectional locomotion in both walk and trot gaits.At a given locomotion speed,the stability margins for the robot during walking and trotting were 27.25%and 37.25%higher,respectively,than in the scheme without CoM planning.The control strategy with energy consumption optimization(ECO)reduced the energy consumption of the robot in walk and trot gaits by 11.25%and 13.83%,respectively,from those of the control scheme without ECO.

Nanomechanical vibration profiling of oocytes

The beginning of a mammalian life commences with a fertilized oocyte.The study of oocytes is certainly one of the most intriguing scientific questions of our time.Herein,we studied oocytes from a mechanical perspective and characterized the typical life activities of oocytes by nanomechanical vibrations.During the development of oocytes from the germinal vesicle(GV)stage to the zygotes,the GV stage oocytes induced a significant nanomechanical vibration,compared with the oocytes in meiosis I(MI)and meiosis II(MII)stages and zygotes.We analyzed the characteristics of mechanical vibrations of oocytes,including the amplitude as well as the frequency.It showed that the amplitude and frequency of nanomechanical vibrations induced by oocytes were caused by the cytoskeleton(microfilaments)and the distribution of metabolic characteristics(mitochondria)within oocytes.This work provides a new perspective for clinical quality assessment and basic research of oocytes,and can open new doors for development of life science.